Drowning
in Noise

Noise Costs
of Jet Skis
in America

A Report for the
Noise Pollution
Clearinghouse

by Charles Komanoff
& Howard Shaw, Ph. D.

APRIL 2000

Disclaimer

“Jet Ski” is a registered trademark of Kawasaki Motors Corp., U.S.A. In this report we use “jet ski” (in lower case) to denote a generic class of watercraft that is popularly known and commonly referred to by that term. We do not mean to single out Kawasaki for criticism, nor do we assert or imply that Kawasaki’s products are noisier than those of their competitors.

The term “personal watercraft” is often used interchangeably with “jet ski,” particularly in legal and regulatory contexts. However, “personal watercraft” is in some respects a misnomer, since jet skis increasingly are designed to carry two or more people. In addition, many non-motorized craft usable by one person, such as kayaks, canoes, small rowing shells and windsurfers could (perhaps even more aptly) be characterized as personal watercraft. (Note that “windsurfer,” which we use generically here, is also a trademark when capitalized.) Another term seen in this context, “thrill craft,” is inappropriate for this report because it includes other ultra-fast boats.

The term “jet ski” in its generic sense is firmly established in popular usage. See, for example, Time magazine (June 14, 1999), the New York Times (Sept. 16, 1998), and LakeLine magazine (June 1994), among many others. In the New York Times article cited, it was noted that personal watercraft are “commonly known as jet skis,” and that term was used in the headline. We continue in that vernacular tradition.

Contents

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1. Summary of Findings

Context. People don’t like noise and will pay to avoid it; witness the reduced market value of houses near airport runways and highways. In this report, we estimate, in quantitative terms, just how annoyed beachgoers in the United States are by the sound of jet skis(1) operated nearby.

We do this through a quantitative model that estimates the monetary value of the “disamenity” (lost enjoyment) that jet ski noise introduces into beach environments in America. Our results, expressed in dollars, are what beachgoers would pay to rid lake, bay, river and ocean beaches of jet ski noise — if there were an entity that would take their money and turn off the noise.

We present two types of estimates: the “annoyance” cost of jet ski noise itself, and the effectiveness of possible strategies to reduce this cost. Other social and environmental costs of jet skis, such as water and air pollution, harm to swimmers and wildlife, etc., are discussed in Section 9, but only summarily; our subject here is jet ski noise and its cost to beachgoers.

Estimates of Jet Ski Noise Costs

National jet ski noise costs: The 1.3 million jet skis in the United States impose approximately $900 million of noise costs on U.S. beachgoers each year.(2)

Noise costs per jet ski: The average jet ski imposes $47 of noise pollution costs on beachgoers in the course of a day’s use. Since the average jet ski is used 15 days a year, it imposes approximately $700 of noise costs on beachgoers each year.

Future growth in jet ski noise costs: With the number of jet skis in use growing by 100,000 a year, the total noise cost will continue to increase. Even if all jet skis sold after 2000 are substantially quieter (by 5 decibels) than current models, jet ski noise costs to beachgoers nationwide in 2005 will be approximately $1.07 billion, or 18 percent greater than the year-2000 total.

These figures do not include the noise costs (including reduced property values) to residents of waterfront areas in range of jet ski noise, or to canoeists, kayakers and other boaters, or to hikers on nearby trails. (These are noted separately on pp. 6-7.)

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Table 1: Noise Cost to Beachgoers per Day from One Jet Ski

Beach types are defined in Table 3 on p. 34.

Jet ski noise costs by beach type: We define beaches as popular, secluded or intermediate-use, based on beach-user population density; and also divide them into “lake-type” beaches (a category that also includes beaches along bays, rivers and canals) or ocean beaches. As Table 1 shows, jet ski noise costs per beachgoer are highest at secluded lakes. On the other hand, noise costs per jet ski are highest at popular beaches, since more people are affected.

Table 2: National Jet Ski Noise Costs to Beachgoers, per Year

Figures in table are derived in Section 6.

According to industry surveys, some 92% of jet ski usage is on lake-type waters, with the remaining 8% on oceans. We assume that 60% of usage is on secluded waters, while the other 40% is split equally between intermediate-use and popular water bodies. With these assumptions, the total national noise cost to beachgoers from jet skis is

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just over $900 million a year. As Table 2 shows, roughly half of the total is experienced on popular lakes, one-fifth is on intermediate lakes, 15% is on popular ocean beaches, and 12% is on secluded lakes. All lake-type beaches (lakes, bays, rivers and canals) bear $732 million in jet ski noise costs, or 81% of the total.

Why Jet Ski Noise Is So Annoying. Jet ski noise is different from that of motorboats. The heart of the difference, and the crux of the jet ski noise problem, is that jet skis continually leave the water. This magnifies their noise impact in two ways.

First, minus the muffling effect of the water, the jet ski engine’s exhaust is much louder, typically by 15 dBA. As a result, an airborne jet ski has the same noise impact on a listener at the water’s edge as an in-water jet ski 8 times closer, or the same as 32 identical in-water jet skis at the same distance.

Second, each time the jet ski re-enters the water, it smacks the surface with an explosive “whomp” — sometimes with a series of them.

Leaving the water is central to the fun of jet skiing; for many jet skiers, the ultimate thrill is to take to the air and bounce off the water repeatedly. But jet skis don’t have to deliberately jump to leave the water. Because of the short hull, a jet ski ridden fast on even a slightly choppy surface will lift out of the water naturally, eliminating the water’s sound-muffling action and creating that jarring whomp.

And that’s not all. The direct noise-amplifying effect of leaving and re-entering the water is compounded by the variable nature of the noise. Rapidly varying noise is much more annoying than constant noise, as decades of psycho-acoustics research have established. A varying noise commands the hearer’s continuous attention, making it especially bothersome. This phenomenon has been largely overlooked in the jet ski controversy. We have quantified its effect here, enabling us to capture the full and unique impact of jet ski noise.

Strategies to Reduce Noise Costs. Three broad approaches have been suggested to reduce jet ski noise costs to beachgoers:

• develop quieter jet skis;
• require jet skis to operate further from shore;
• restrict jet ski usage to fewer bodies of water.

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We have found that only the third approach — restricting usage — holds real promise for significantly reducing jet ski noise costs in a region or nationwide. (Banning “wake-jumping” is infeasible; see Section 8. Taxing users for jet skis’ environmental damage is discussed further below. “Temporal segregation” is treated briefly in Section 8.)

We estimated the measures necessary to reduce nationwide jet ski noise costs to beachgoers by three-fourths from today’s levels by the year 2005, while assuming that the number of jet skis in use will rise from 1.3 million to 1.8 million. Meeting this goal would require banning jet skis from 90% of all U.S. lakes, bays, rivers and oceans.

Alternatively, the same objective can be met by banning jet skis from 82% of waters, and requiring jet skis at the remaining sites to operate at least a quarter-mile from shore. (If the half a million jet skis projected to be purchased between now and 2005 are 5 decibels quieter than current models, on average, then the 82%-complete ban could be relaxed slightly, to a level of 78%.)

By themselves, “minimum-distance” laws will not cure the problem of jet ski noise to beachgoers. We estimate that barring jet skis from operating within 500 feet of shore would reduce nationwide noise costs from current jet skis by only 27%; moreover, this improvement would be wiped out by growth in usage in five years. Even a quarter-mile rule would only reduce current jet ski noise costs by 48%, and by 2005 this reduction would be trimmed to 28%.

Perhaps surprisingly, the introduction of quieter models will not reduce total jet ski noise costs at all. Even if every new jet ski sold after 2000 were built with modified engine designs that some manufacturers claim reduce noise emissions by 5 decibels, the national jet ski noise cost to beachgoers in 2005 would still be 18% greater than today, according to our calculations. Because they apply to new models and not to jet skis currently in use, technological refinements to make jet skis quieter will not lessen the absolute burden to beachgoers, nor even prevent that burden from growing.

Taxes on jet ski noise: Another approach to reducing jet ski noise costs is to “internalize” them by taxing their sale or use. We estimate that a tax rate corresponding to just half of a typical jet ski’s noise costs would drive up the purchase or rental price to an extent that a third of all jet ski use — and noise — would be eliminated. Higher

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taxes capturing a larger share of jet ski noise costs, as well as their pollution and injury damage to humans, wildlife and marine ecosystems, would eliminate larger fractions of jet ski use and noise.

Substantially reducing noise costs of jet skis requires banning them
from most waters, and mandating that they stay at least a
quarter-mile from shore at remaining areas.

Jet Ski Costs Apart From Beachgoers

Non-beachgoer noise costs: Using the framework developed here to estimate jet ski noise costs to beachgoers, but employing rougher estimates for some key parameters, we have estimated that jet ski noise costs to owners of waterfront property in the U.S. are on the order of $230 million a year; similarly, jet ski noise costs to non-motorized boaters (e.g., canoeists, kayakers, and windsurfers) are on the order of $120 million annually. These figures are not included in the noise costs to beachgoers given above.

Other costs of jet skis: After reviewing the literature on both jet ski emissions and the health costs of air pollution, we have estimated that air pollution from jet skis imposes at least $240 million a year in health costs to Americans. Other costs from jet skis, including

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pollution of marine environments, habitat and wildlife destruction, and endangerment and injury to humans, are mentioned but not quantified later in this report. These costs are treated in Section 9.

National jet ski noise costs to beachgoers are now over $900 million
and could reach $1.25 billion in 2005 (see Section 6). Noise costs
to property owners and water recreationists are estimated roughly
in Section 9.

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2. Introduction

This report is addressed to policymakers, resource economists and, above all, the many people throughout the United States whose pursuit of happiness at our nation’s shorelines and beaches is diminished or made impossible by noise from jet skis.

DROWNING IN NOISE presents a novel approach to the issue of jet ski noise. The authors and publisher hope it will prove to be a powerful tool in encouraging jurisdictions to act against the enormous and growing vexation of jet ski noise.

The centerpiece of this report is a model that quantifies how much beachgoers are being made to sacrifice their own pleasure and well-being because of noise from jet skis. The model estimates the total amount of jet ski noise to which people at a beach are subjected, and then translates their displeasure due to this noise into dollars. The resulting dollar total expresses how much, and how often, noise from jet skis degrades an experience treasured by most Americans: a day at the beach.

Translating noise into dollars of “disamenity”(3) is not new, although DROWNING IN NOISE is the first noise-cost analysis of jet skis, to our knowledge. Still, quantifying the cost of noise is not a widely familiar concept. Our approach is based on the idea that the value that people derive from recreational activities (like visiting a beach) can be estimated, using measurable factors such as the amount of money that they spend getting there, as well as survey data on the value of beach recreation. To calculate how much the value of “beachgoing” is degraded by jet ski noise, we draw on studies that have measured the effect of environmental noise on residential property values.

When empirical values are fed in — the jet ski is so many feet offshore, it is so many decibels loud at the source, the beach is so many feet wide and deep, the beach is “popular” or “secluded” with a corresponding background noise level, the average beachgoer spends so many dollars to be at the beach — the model yields estimates of the value of people’s time at the beach, the additional decibels of jet ski noise to which the beachgoers are exposed, and the dollar value (the cost to them) of their reduced pleasure of being at the beach.

To be sure, all these variables differ over a wide range — no two beachgoers are exactly alike, or occupy the same position on the

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beach, or are equally sensitive to noise; no two jet skis make the same noise or operate at a uniform distance from the beach; and so forth. Accordingly, the jet ski noise model incorporates random elements, so that the variables may encompass a range of plausible conditions.

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The model then repeats, many times, its calculations of excess noise and its cost. The averages of these “iterations” are statistically superior to the result of merely multiplying a series of average values.

The model can be run in this way for particular real-world beaches or for idealized “types” of beaches (e.g., a “popular lake”). The resulting estimates of jet ski noise costs are often large — large enough that hitherto passive regulators and legislators might be made to take notice. For a typical popular lake beach, the noise from a single jet ski operating close to shore for a few hours robs the collective beachgoers of a hundred dollars in lost enjoyment for the day. For the nation as a whole, we estimate that the noise annoyance costs of jet skis to all U.S. beachgoers over the course of a year is slightly over 900 million dollars.

These may seem large costs to associate with what is often considered a mere “nuisance.” But jet skis are now ubiquitous in America — an estimated 1.2 million were in use in 1999, with 1.3 million expected to be operating in 2000, the “base year” for this report. And beachgoing is an enormously popular and valued activity. The $900 million annual cost of jet ski noise is the sum of the costs from close to a billion individual occasions of “disamenity” — almost a billion beach-days marred, or ruined altogether, by the roar and whine of a jet ski.

Our estimates of the average noise cost imposed by one jet ski on each of these occasions reflect the wide variations in beach environments and users, and range from around 40 cents per beachgoer on a noisy ocean beach, to seven dollars per visitor to a quiet lake shore. While there is necessarily an element of judgment in many of the underlying assumptions, both the model and our valuations of its parameters are rooted in the literature of acoustics, economics and mathematics. If our aggregate estimate of jet ski noise costs seems large, that is the consequence of turning thousands of formerly tranquil waters into aquatic go-cart tracks.

DROWNING IN NOISE was undertaken to make these costs clear and comparable to other social costs. That a lone jet ski operating near shore for just a few hours can disturb hundreds of people along the beach is widely understood. That the aggregate costs associated with these same disturbances can reach a hundred dollars or more gives this understanding greater concreteness.

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In a very real sense, the tribute of “disamenity” extracted by jet ski users from everyone else in earshot is a kind of robbery. With the full extent of the cost now apparent, regulatory and legislative actions — usage restrictions, stringent equipment standards, perhaps noise taxes — should follow.

The Noise Pollution Clearinghouse and the authors of DROWNING IN NOISE stand ready to help individuals, advocacy groups and government agencies evaluate jet ski noise costs and take action to minimize and eliminate them. We hope that DROWNING IN NOISE will stimulate specific analyses of jet ski noise costs at shorelines of concern, as well as assessments of other noise annoyance costs.

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3. Jet Ski Noise Is Different

Less than two decades since they were introduced, jet skis have become ubiquitous on U.S. waterways. Sales of jet skis currently run at around 150,000 a year; older models are being scrapped at only a third of that rate, and an estimated 1.3 million “personal watercraft” are now operating on the nation’s bays, lakes, rivers and oceans.

In reaction to the nearly constant intrusion of jet ski noise on thousands of beaches and shorelines, organizations of anglers, canoeists, nature-lovers and beachgoers have campaigned strenuously to limit jet ski use. Prodding by national and local citizens’ groups has resulted in the banning of jet skis from more than two dozen units of the National Park Service, including Yellowstone, Everglades and Grand Canyon National Parks, and from dozens of prized lakes from Lake Tahoe in the Sierra Nevada range to the Stockbridge Bowl in western Massachusetts.(4)

Vermont now bans jet skis from lakes and ponds smaller than 300 acres, effectively limiting them to lakes at least a half-mile across,(5) and the machines have been barred from waterways of the San Juan Islands of Washington State and of Marin County, north of San Francisco. Some jurisdictions, including San Francisco County and south Florida’s Monroe County, require jet skis to keep a considerable distance — in some instances, almost a quarter-mile — from shore.(6)

Yet bans or operating limits are still exceptional. Restrictions have been adopted piecemeal, and only over bitter resistance by jet ski manufacturers and user groups. For the most part, following America’s laissez-faire tradition toward motorized recreation, jet skis have been permitted to proliferate, almost as-of-right, while objectors must bear the burden of proving harm and seeking redress. Throughout the 1990s, in fact, while citizens were scrambling to marshal facts and mount grassroots campaigns, the jet ski industry and user groups were cultivating influence and entering mainstream culture.

Manufacturers and users insist that jet ski noise is little different from noise generated by other motorized watercraft.(7) But their arguments appear to ignore fundamental differences between jet skis and motorboats. While jet skis can sometimes be observed operating no more loudly than motorboats, as a general rule jet skis are considerably noisier and more disturbing. Three differences stand out:

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1. Jet skis are designed and used differently from motorboats, in ways that typically make them far more annoying to other people in the same environment.

With their small size and shallow draft, jet skis can venture closer to shore than motorboats. Moreover, whereas motorboats are used for many different reasons, from excitement to relaxation, jet skis are designed and marketed for only one reason: the thrill of speed. Jet skis are not used for fishing or cruising; a jet ski is seldom driven at

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less than full throttle. Motorboaters as often as not head for a fishing or picnicking spot, then douse the engine when they get there. But jet skiers seldom have a destination in mind. Rather, they use their vehicles continuously as a recreational end in themselves.

2. The heart of the difference between jet skis and motorboats, and the crux of the jet ski noise problem, is that jet skis continually leave the water. This magnifies the noise in two ways. First, without the muffling effect of the water, the engine’s exhaust is much louder — typically by 15 dBA; an airborne jet ski has the same noise impact on a listener at the water’s edge as an in-water jet ski 8 times closer, or the same as 32 identical in-water jet skis at the same distance. Second, each time the jet ski re-enters the water, it smacks against the surface with an explosive “whomp” — sometimes with a series of them.

Leaving the water is central to the fun of jet skiing. For many jet skiers, the ultimate thrill is to take to the air and bounce off the water repeatedly. This is easily accomplished — by jumping the wake from a passing motorboat, or from another jet ski (often in a duet of mutual wake creation and riding), or from one’s own machine. But jet skis don’t have to deliberately jump to leave the water: because of the short hull, a jet ski ridden fast on even a slightly choppy surface will lift out of the water naturally, eliminating the water’s sound-muffling action and creating the jarring whomp.

Noise Levels of Common Sources (Cowan, 1994)

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So whether by the operator’s intent or the vehicle’s design or both, jet skis wind up “out of the water” much of the time — certainly far more than all but the occasional (and also annoying) “cigarette” boat to which jet skis are sometimes likened. And not only does this raise the jet ski’s instantaneous noise emission by a very considerable 15 dBA on average; the effect is vastly compounded by the variable nature of the noise.

An established finding of psycho-acoustics is that rapidly varying noise is much more annoying than constant noise — even a constant noise that is equal in intensity to the loudest instantaneous noise in a series. This is a truth known by experience to anyone who has been repeatedly startled or disturbed by a loud but intermittent sound, like a jackhammer at a construction site. A varying noise commands the hearer’s continuous attention, making it especially bothersome. This ensures that jet skis’ whirring and whomping noises, varying from moment to moment, will be much more annoying than the relatively constant sounds produced by other watercraft. (For quantification of this annoyance, see sidebar, “Variable Noise is More Disturbing,” on p. 21.)

3. The final characteristic that distinguishes jet skis from motorboats is their rapid maneuvering and frequent speed changes. In addition to jumping wakes, jet skis are designed and marketed for weaving, sharp turning, spinning doughnuts and generally erratic throttle use. As a result of these maneuvers, the jet impeller has no consistent water “throughput,” and thus, no consistent load on the engine. Consequently, the engine’s speed rises and falls from moment to moment with each maneuver. The result is a penetrating whining sound, rising and falling rapidly in pitch like a dentist’s drill and demanding the attention of anyone within earshot.(8)

We estimate that jet skis are operating “out of the water” or in the rapid maneuvers just described, around 20% of the time. Both involve not only elevated noise emission levels but also varying — hence, unusually annoying — sounds.

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4. Jet Ski Noise Costs for One Beachgoer

The analytical core of this report is a procedure for estimating the noise increment — the increase above background noise levels — that a single jet ski causes for each beachgoer within range of its noise, and for translating the subjective annoyance caused by this excess noise into dollar terms. Later we generalize this into cost estimates for a “population” of beachgoers at one beach, and, ultimately, for the entire United States. Thus the analysis starts with two key questions about a “representative” beachgoer: how much louder do one or more jet skis render the beachgoer’s noise environment, and how do we represent the extra noise economically, in dollars of lost amenity?

These estimations unfold through a series of steps, each involving mathematical relationships specifying, for example, the rate at which noise diminishes with distance, or how a fluctuating noise compares in annoyance value with a constant noise. As well, a wide variety of “parameters” must be specified, e.g., what is the beach’s background noise level, without the jet ski, and how much annoyance occurs per unit of noise increment above that background?

Noise is a complex phenomenon, not least in its basic unit of loudness, the decibel (dBA), which is the logarithm of a physical quantity, acoustic power (see sidebar on previous page). Nor is it usual to see the impact of noise expressed in dollars. Accordingly, this section outlines and explains jet ski noise estimation and costing step by step. (Readers interested in a more detailed account of the technical nuances may refer to the Appendix.)

It will be helpful to keep the following points in mind:

Laws of Noise

• Noise from a “point source” such as a jet ski diminishes rapidly over distance, with the sound intensity declining in proportion to a power of the intervening distance. Based on measurements which we discuss in Part 1 of the Appendix, we assume that this decline is in proportion to the 1.661-th power over water, and to the 1.993-th power over land. This corresponds to a decline of 5 dBA per doubling of distance over water (6 dBA over land). See Fig. 1.

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• In measuring and discussing noise from jet skis it is important to distinguish between measurements taken at the source (a jet ski) and those taken at the position of a hearer (a beachgoer).
• When two simultaneous noise sources combine, the combined loudness is not simply the sum of the two dBA values. Rather, the dBA values must be converted back to raw acoustic power values; these are added and the logarithm of this sum, multiplied by 10, gives the dBA value for the combined noises. This implies that the louder source contributes much more to the combined loudness than a comparison of the two dBA values would suggest. Whenever the jet ski is louder than the background noise level, the combined noise level experienced by the beachgoer will be only slightly more than that of the jet ski alone. Informally, we can say that quieter sounds (the background noises in this case) are almost “swamped” or overwhelmed by louder. See Fig. 3.
• The noise increment due to an additional noise (from the jet ski) is calculated by subtracting the background noise level from the combined noise level discussed above (the additional noise combined with the background noise).
• Fluctuating noise is much more annoying than steady noise; this “psycho-acoustical” phenomenon helps explain the exceptionally disturbing effect of the repeated noise surges when a jet ski leaves the water. This is quantified by Robinson’s Formula (see sidebar, next page, and Fig. 5).

Key Noise Cost Precepts

• The dollar “value” of a person’s day at the beach can be estimated by considering the person’s expenses in traveling and visiting the beach, and using that total to establish a lower bound for the economic value of the day. (In fact, the value of the day clearly exceeds what the beachgoer had to pay, by some additional amount, or why would she bother?)
• How much an increment of noise detracts from the enjoyment value of a beach day can be approximated with the help of estimates of the diminution of residential property values due to noise. We call this value the Noise Depreciation Index (NDI).

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• The NDI is assumed to be constant, so that any increase in noise level of 10 decibels (dBA) always produces twice as much amenity loss as any increase of 5 dBA, independently of the base noise level.

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Input Assumptions

We now present the assumptions used throughout DROWNING IN NOISE to calculate the noise cost for a single beachgoer from a single jet ski. See the Appendix for derivation and justification for each.

· Jet ski distance from shore: between 50 and 10,000 feet, but heavily weighted toward the lower end (the additional distance from the water’s edge to the beachgoer is treated in Section 5). In the illustrations here, the distance between jet ski and beachgoer is assumed to be a constant 160 feet — much less than typical.

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• Jet ski noise level in water: 80 dBA (measured at a distance of 20 feet from the jet ski).
• Jet ski noise level out of water: 95 dBA (also at 20 feet).
• Jet ski fraction of time out of water (or maneuvering rapidly): 20%.
• Noise attenuation: across water, by 5 dBA for each doubling of distance beyond 20 feet from the source; across land, by 6 dBA per doubling of distance.
• Jet ski duty cycle multiplier (reflecting the fact that a jet ski “day” and a beachgoer “day” may not completely coincide): 2/3.

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• Beachgoer population density: one person per 10,000 square feet at “secluded” beaches; one person per 1,000 square feet at “intermediate” beaches; one person per 100 square feet at “popular” beaches. (These correspond to roughly 4.4, 44 and 440 people per acre, respectively; see Fig. 2.)
• Beach background noise level: 45 dBA at secluded lake beaches (actually “lake-type” beaches, a category that includes lakes, bays, canals and any other waters with little or no noise from surf or cascading water); 55 dBA at intermediate lake beaches; 65 dBA at popular lake beaches and all ocean beaches regardless of population density. See Fig. 2.
• Beachgoer mean beach-day value: $30 at secluded beaches; $20 at intermediate beaches; $10 at popular beaches. (See Fig. 6. These are mean values, with some variation; see Appendix, Part 1.)
• Noise Depreciation Index (NDI) (fractional extent to which a 1 dBA increment to the noise level reduces the beachgoer’s enjoyment value of the day; see Fig. 7): 1.0%.

“Costing” the Excess Noise Imposed on Beachgoers

Value of a Beach Day

The accompanying illustrations depict jet skis raising beachgoers’ prior background noise levels. We now discuss how we translate these noise increments into dollars of negative value, or “disutility” in the parlance of economists.

The process begins with estimates of spending by the beachgoer to get to (and from) the beach, as well as other associated costs. These “actual expenditures” provide a lower-bound estimate of the economic value the beachgoer attaches to the day at the beach, since she must derive at least enough enjoyment to offset the cost of getting and being there (travel, parking, admission, extra food costs, etc.); otherwise, the visit wouldn’t be worth the expense of the trip.

In the Appendix, we discuss estimates of what beachgoers actually spend to access beaches in America, compiled by economists who study outdoor recreation. From these studies, we estimate that, as rough averages, visits to “popular” beaches, which by nature are easy to reach, cost beachgoers just $5 a day; visits to harder-to-reach

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“secluded” beaches cost considerably more, $15 on average; visits to “intermediate” beaches entail spending the in-between figure of $10.

Consider a visit to an intermediate beach. The $10 expenditure represents only part of the value of the beach experience. Virtually all spending contains an element of value called consumer surplus, denoting the additional value to the buyer beyond the purchase price. I pay the $1.00 store price for a quart of milk, but I would have paid up to, say, $1.40; the 40¢ difference between the milk’s cost to me

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and its value is my consumer surplus. Similarly, I may pay $299 to fly to London and back, but if I would have paid as much as $499, my consumer surplus for the fare is $200.

Economists have studied the consumer surplus associated with different kinds of expenditures. For discretionary purchases such as travel to a beach, consumer surplus is considered to be roughly equal in magnitude to the monetary expenditure.(9) That is, if a group of people paid an average of $10 each to get to an intermediate beach, the beach provided each of them with an average total value or enjoyment of about $20. Of this amount, one half offset the cost of the trip, and the other half corresponded to their consumer surplus, or net enjoyment over and above their direct outlay. The $20 total value of the beach experience is the sum of the actual expenditures and the consumer surplus.((10)

Value Loss from Adding Noise to a Beach

Next, we estimate the “degradation” of the beach experience due to the noise a jet ski imposes on the beachgoer. What we are seeking is a “Noise Depreciation Index” (NDI) capturing the extent to which a 1 dBA increment in noise level reduces the beachgoer’s enjoyment value of the day.

Beachgoers’ preference for quiet has never been quantified directly. Accordingly, our point of departure is people’s willingness to pay a premium to live in quiet as opposed to noisy neighborhoods, which has been extensively studied since the 1960s.

How similar are homeowners and beachgoers’ desire for quiet? Certainly, both groups want a noise-free environment; indeed, they are the same people, in different settings. Still, expectations and standards vary from one setting to the other; we believe that if anything, quiet is more central to beach enjoyment than to property values. Competing criteria such as safety, schools, transportation and neighborhood stability are important for housing values, whereas environmental and aesthetic considerations dominate in recreational settings.

This is not to say that beachgoers place quiet above all else; but for most, relief from the quotidian burden of intrusive noise — especially the ubiquitous noise of motors — is an important part of the expected and desired ambiance. Moreover, one can mitigate noise to

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some degree on one’s own property by going indoors, shutting windows, or installing sound-insulating materials or muffling devices; a beach affords no such escape.

As we discuss in reviewing residential property studies in Part 5 of the Appendix, we believe that an NDI of 1% represents a reasonable estimate of the effect of noise on beachgoers’ enjoyment value of the day. It implies that to eliminate 10% of the enjoyment of a day at the beach, the noise increment due to the jet ski (or, equivalently, passing airplanes, dune buggies, etc.) must be 10 dBA.

That is an effect equivalent to replacing the noise level of a typical suburban area with that of a typical urban area or a busy office, as indicated in the table of noise levels on p. 14. Intuitively, it seems unlikely that an NDI of 1% overstates the degree to which each additional decibel reduces the beachgoer’s enjoyment value of the day.

Of course, people who attach greater value to quiet would tend to have a higher NDI, while others drawn to the beach primarily for “activity” would have a lower NDI. We believe an NDI of 1% is a reasonable mean encompassing a range of relative preferences between quiet and noise.

Jet Ski “Duty Cycle”

The discussion to this point assumes a jet ski hovering around the same area and operating nonstop all day. The first assumption is loosened in our model by treating the jet ski’s distance from shore as a “random variable,” as we discuss in Section 5. (Note that if the jet ski moved parallel to the beach, the same noise impact would simply be inflicted upon a different group of beachgoers, so the cost to all beachgoers would essentially be the same in our model. In fact, this understates the actual noise impact, because of noise-level variation as discussed in the sidebar on Robinson’s Formula, p. 21.)

The second assumption, pertaining to usage or “duty cycle,” requires us to qualify the model in Fig. 7. The issue is not that a jet skier may take an occasional break; since several users customarily take turns riding a single jet ski, most machines are in use nearly constantly. Rather, it is one of duration and timing of use.

Most beach and water use, by beachgoers and jet skiers alike, takes place over a six-hour period between the late morning, say 11 a.m.,

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and the late afternoon, around 5 p.m. However, the average “beach- goer day” and “jet ski day” are both considerably shorter than six hours. We assume that a jet ski is driven for an average of three hours a day,(11) and that a beachgoer day similarly averages three hours long.

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Thus, if the jet skier arrives at the beach early in the day and also leaves early, and if the beachgoers arrive and depart late, they miss each other, and there is no noise annoyance to the beachgoers. Conversely, if the jet skier and the beachgoer arrive (and depart) at the same time(s), then the “beachgoer day” is fully saturated with noise, and annoyance, from the jet ski.

Perhaps surprisingly, the mathematical average (“expected value,” actually) of the overlap between the beachgoer and the jet ski is not one-half, but two-thirds. That is, if a jet skier and a beachgoer each spend three hours at the beach (both as contiguous three-hour blocks of time) over the course of a six-hour period of possible daily beach use (11 a.m. to 5 p.m.), the beachgoer will have the jet ski’s presence about two-thirds of the time.(12) Accordingly, two-thirds of the beachgoer’s beach-day value is affected. This requires that the calculation of lost amenity to this point, which assumes a full-day impact (with the value of a beachgoer day multiplied by the NDI and the excess decibel level), be multiplied by 0.67, as Fig. 8 illustrates.

Note that this simple two-thirds factor overlooks a psychological subtlety. Even after a jet ski has left the area, a beachgoer who has suffered through the noise annoyance has no assurance that the machine won’t return. Indeed, if she expects the cessation to be only temporary, then an anticipatory disturbance will likely persist through her remaining time at the beach. Accordingly, the two-thirds duty-cycle factor appears likely to understate jet ski noise costs for many beachgoers.

Factoring in the “duty-cycle factor” of 0.67, a jet ski at a 160-foot distance from a beachgoer typically imposes amenity losses ranging from a little under $1.50 per person at a popular beach, to almost $9 at a secluded lake beach, as Fig. 8 shows. In the “average” case reflected in Table 1 (p. 2), the per-beachgoer noise cost from one jet ski ranges from around 40 cents at a popular ocean beach to $7 at a secluded lake beach.

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5. Jet Ski Noise Costs for an Entire Beach

Introduction. In the previous section we outlined a model for estimating jet ski noise annoyance to one beachgoer on a specific beach, when a jet ski is a constant distance from shore. Here we describe an aggregate model for estimating noise costs for all of the beachgoers on six different classes of “beach types,” such as a “secluded lake” or “popular ocean,” with the jet ski distance from shore varying substantially. We believe the results are realistic estimates of the noise annoyance costs that jet skis impose on a beach full of people.

These estimates function as building blocks to estimate the aggregate disamenity of jet ski noise for the entire United States, in Section 6. They also may be used to assess proposals to control or eliminate jet ski noise in different beach environments, as we do in Section 8.

As noted earlier, we characterize beach types as either lake (bays, rivers and canals are subsumed under lakes) or ocean; and each beach is popular, intermediate or secluded, based on population density.

The beach (shoreline) lengths are assumed to range between 80 and 800 feet for lakes; the more expansive ocean beaches are assumed to vary in length between 200 and 2000 feet. Similarly, beach minimum and maximum depths (distance from water’s edge to the rear of the beach) are 20 and 80 feet, respectively, for lakes; and 50 and 200 feet, respectively, for oceans. (Dimensions are tabulated in Table 3 below.)

To calculate beachgoers’ noise increment from the jet ski, we must locate these beachgoers on the beach. We assume that the jet ski is evenly centered with respect to the beach, so that a perpendicular line drawn from the jet ski to the shore and extending to the back of the beach would divide the beach into two equal segments. We then distribute the beachgoers along the beach in equal left-to-right intervals, while letting their distance from shore vary randomly.(13) In effect, each beachgoer “commands” an area on the beach determined by the beach type and its associated population density.

For the jet ski we specify minimum and maximum distances from shore of 50 and 2,500 feet (roughly one-half mile), respectively, for lake-type beaches; and 50 and 10,000 feet (roughly two miles) for ocean beaches. The vast majority of jet ski operation appears to be within this range, both because most lakes, rivers, canals and bays are less than a mile across, and because jet skiers tend to operate close to

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shore in any event. To reflect these phenomena, we locate the jet ski at a distance from shore given by a probability density that recognizes that jet skis tend to operate close to shore rather than very far away (see Appendix, Part 2).

Even so, our model produces an average jet ski distance from shore of 530 feet for lake (and bay and river) beaches, and an average distance of 1,365 feet for ocean beaches. Note also that the model assumes, for the sake of conservatism and simplicity, that at any particular (simulated) beach, the jet ski remains a constant distance from the shore. In fact, of course, the jet ski actually moves toward and away from shore over a rather wide range, causing additional noise level variation, and hence, additional disamenity that is not included in our model.

Now we need to account for jet ski “clustering.” Many jet skis are driven in pairs or in larger groupings. We assume that the average jet ski is part of a cluster of 1.6 jet skis (a statistical artifact akin to the proverbial “2.1-child-family”). This has the effect of adding just over two decibels (2.04 dBA, to be exact) to the 80 dBA mean emission level we have assigned to a single jet ski.(14)

To perform the actual calculations of excess decibels and disamenity costs for each beach, we adopt what mathematicians call a “Monte Carlo” approach (named for Monaco’s casinos, not for its beaches!). For each of the six beach types, we “computer-simulate” many (10,000) beaches of that type, each characterized by random values fitting the parameters defining that type.

Thus, to estimate the noise costs from a jet ski at, say, an intermediate lake, the computer constructs 10,000 such lakes — each with a population density of one beachgoer per 1000 square feet, with beach length varying from 80 to 800 feet and beach depth varying between 20 and 80 feet, as noted above. For each lake, the computer randomly spreads people along the beach and also assigns a jet ski to a distance between 50 and 2,500 feet from shore (between 50 and 10,000 feet for ocean beaches).

Each beachgoer’s noise-disamenity cost is then calculated from the excess decibels she experiences and the value she assigns to a beach day; and the sum of these costs for the different beachgoers becomes the jet ski noise cost for that one “trial.” That cost is then averaged with the costs calculated in the other 9,999 trials, giving the

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results for the intermediate beach in the table on this page. (See Appendix, Part 2, for details.)

Jet Ski Noise Costs at Typical Beaches. Table 3 presents our estimates of the noise costs imposed on beachgoers at one beach by a jet ski cluster of 1.6 jet skis over the course of a day. The beach “input assumptions” are displayed in regular type, while the rows in boldface show the jet ski noise results — the additional noise experienced by the average beachgoer, the disamenity cost per beachgoer, and the disamenity summed across all beachgoers. The three bottom rows represent mean disamenity values for beaches of that beach type, computed over many beaches of that type.

The table shows that the added noise from a typical jet ski cluster is highest at the quietest beaches, with an average increment over back-

Table 3: Jet Ski Noise Costs per Beach per Day, by Beach Type

“Lake” subsumes bays, rivers and canals as well as lakes. Jet ski clusters average 1.6 jet skis each and are assumed to generate 82.04 dBA in water (80% of time) and 97.04 dBA out of water (20% of time), and to be randomly distributed between 50 and 2,500 feet offshore for lakes, and between 50 and 10,000 feet for oceans, but with closer distances predominating in all cases. Population is mean for each beach type. Utility/person is beachgoers’ mean value of day at the beach, without jet ski noise. Cost/cluster is total noise cost for entire beach, per day. Cost/jet ski equals cost/cluster divided by 1.6, and is not the same as the cost from one jet ski shown in Table 1. Cost/person equals Cost/cluster divided by Population (before rounding). Costs incorporate 0.67 duty-cycle factor.

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ground of 37 dBA at the secluded lake beach and 26 dBA at the intermediate lake beach. The noise increment is lowest at the other beaches (popular lake and all oceans), for which the background noise level is assumed to be a uniform 65 dBA. (The average noise increment is higher (13.7 dBA) for the popular lake than for the ocean beaches (7.6 dBA), because more beachgoers are closer to the jet ski at the smaller lake beach.)

Noise costs per person are highest at the respective secluded beaches, and lowest at the crowded beaches, for two reasons: first, beachgoers at secluded beaches are assumed to place a higher value on their beach day; second, jet skis are more audible at quieter lake beaches. However, the noise cost per jet ski cluster (which is the summation of the per-person noise costs, across all beachgoers) is greatest by far at the popular beaches, as the increase in the population of beachgoers more than offsets the decline in per-person disturbance.

In addition, ocean beaches have higher noise costs than the corresponding lakes. This is because ocean beaches are larger, and thus present more people exposed to the noise.

The costs in Table 3 are averages for typical beaches and typical beachgoers. Actual beaches may be bigger or smaller than the figures shown here. For example, ocean beaches, as we define them, can reach as large as 2,000 feet long by 200 feet deep. A popular beach with those dimensions supports a population of 4,000 beachgoers, or almost triple the population mean shown in the table. The average beachgoer there would experience only a modest noise disamenity from jet skis, just 44¢ on average, but this would aggregate to $1,760 a day when summed over the huge beach population.(15)

At the other end of the scale is the secluded lake beach. By our definitions, lake beaches vary from as small as 1,600 square feet (80 feet long x 20 feet deep) to as large as 64,000 (800 x 80), and average around 22,000 square feet, or around half an acre. Since secluded beaches, by definition, have a population density of just 1/10,000 person per square feet, the average secluded lake beach has only 2.2 people — and is secluded indeed. But both of them would be intensely disturbed by jet skis, with a mean per-person disamenity cost of $7.40, or almost 25% of each beachgoer’s normal beach-day utility of $30. The total noise cost at this beach would be relatively small, however, at $16, because few people would experience the noise.

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6. National Jet Ski Noise Costs

Annual National Jet Ski Noise Costs to Beachgoers. In the previous section we presented estimates of per-day jet ski noise costs to beachgoers for six “beach types”: popular, intermediate and secluded lakes (where the lake category also encompasses bays, canals and rivers), and popular, intermediate and secluded oceans. We now apply those figures to estimate an annual cost of jet ski noise to beachgoers for the entire United States of $908 million.

Calculating the national jet ski noise costs to beachgoers is straightforward, once we specify several assumptions about jet ski usage:

• the number of jet skis in the U.S., and the average number of days they are used per year;
• the extent to which jet skis are used solo or in “clusters”;
• the distribution of jet skis between lake-type and ocean beaches;
• the distribution of jet skis among popular, intermediate-use and secluded beaches.

Number and usage of jet skis in the U.S. — We estimate that during 2000, the “base year” for this report, there are 1.3 million operable jet skis in America, and we assume that they are operated an average of 15 days a year. Both numbers are based on industry sources.(16) Combining the two assumptions yields 19.5 million “jet ski-days” of use per year in the United States.

Jet ski “clustering” — As noted in the preceding chapter, we assume that the average jet ski is part of a cluster of 1.6 jet skis. Accordingly, 19.5 million “jet ski-days” actually impinge on beachgoers as much fewer, 12.2 million, “jet ski-cluster-days” ( = 19.5 million / 1.6 ). Each jet ski cluster is louder than a lone jet ski by 2.04 dBA.

Jet ski distribution between lakes and oceans — The most comprehensive survey of jet ski owners to date, conducted for the jet ski industry in 1995, found that 71% of jet ski riding time is spent on lakes, 19% on rivers, 2% on canals, and 8% on oceans.(17) (Bays were not included as a category.) Rivers and canals (as well as bays) resemble lakes in both beach topography and wave height (which influences the background noise level). Accordingly, we place beach environments into two categories, lakes and oceans, and assign 92% of jet ski use to “lakes” (including rivers, canals and bays), and the remaining 8% to oceans.

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Jet ski distribution among popular, intermediate and secluded beaches — We assume that 60% of jet skis are used around secluded beaches. While a majority of beachgoers congregate at popular beaches, the majority of beaches in America are secluded. (If 60% is too high, then we have understated the national noise cost, since each jet ski has a smaller total noise impact at a low-population beach than at a high-use beach.) We assign the remaining 40% of jet ski use equally (20% each) to intermediate-use and popular beaches. We also assume that the 20%/20%/60% jet ski distribution among popular, intermediate, and secluded beaches applies to both ocean and lake beaches.

From these assumptions, the 12.2 million jet ski clusters each year in the U.S. divide into roughly 6,700,000 at secluded lakes, 200,000 each at intermediate and popular oceans, and varying amounts at the three other types of beaches. Table 4 displays these usage figures and combines them with estimated per-usage costs for each beach type from Table 3, to yield the estimated total annual noise cost of jet skis to beachgoers in the United States.

As Table 4 shows, the estimated annual cost of jet ski noise to beachgoers in the United States is $908 million. An estimated $732 million of costs, 81%, are experienced at lakes, which we assume account for 92% of beaches frequented by jet skis. Popular beaches of either type (lake and ocean) comprise only 20% of beaches but almost 90% of beachgoers. Not surprisingly, they account for $587 million, or 65%, of the national jet ski noise cost to beachgoers.

Table 4: Annual Jet Ski Noise Costs to U.S. Beachgoers

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Noise costs per cluster are per day and are rounded from values in Table 3. Notes from that table apply here. Clusters per year are rounded; for exact values, multiply respective percentages in first row by 12,187,500.

Although secluded beaches are used by just 3% of beachgoers, they account for a substantial $122 million of annual noise costs, which is 13% of the national total. In particular, beachgoers at secluded lakes experience $110 million annually in lost amenity due to jet ski noise. While by definition each secluded lake has few beachgoers, jet ski usage there imposes high noise costs due to the large number of such sites, the high value that visitors to secluded areas place on their recreation day, and the low background noise that makes jet skis particularly audible.

The $908 million total cost per year equates to an average of $698 per year in noise costs to beachgoers per jet ski in the United States, and to $47 per jet ski per day of usage, where a “day” is defined as three hours of usage. That is, in the course of a day’s use the typical jet ski operating in America imposes $47 worth of noise pollution costs on beachgoers. To be sure, jet skis that avoid popular beaches, or remain far from shore and are operated conservatively, or congregate in clusters with other jet skis, impose lower costs. Conversely, jet skis that hover near popular beaches or are particularly loud emitters or operate solo create even more total disamenity.

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7. Caveats

The dollar amounts in Table 4 in the previous section purport to represent what Americans would be willing to pay to rid their beaches of jet ski noise — if there were an agency that would take their money and turn off the noise. Are these results plausible?

We believe so. To be sure, $908 million a year may seem high for damage that is primarily aesthetic.(18) But this figure has been derived meticulously and appears commensurate with the nationwide level of jet ski usage, as well as the frequency of beachgoing and the importance Americans attach to it.

At the same time, we recognize that this national noise-cost figure is built on many assumptions — the sidebar on p. 40 shows 17, of which 7 pertain to an individual jet ski, 2 describe an individual beachgoer, another 4 concern the beach type, and 4 generalize from a single beach to the entire country. While some of these parameters are known to a high degree of precision — e.g., number of jet skis in the U.S., or rate of noise dissipation — others had to be approximated and may only be accurate to a factor of two. Verifying and fine-tuning these parameters is an area for future research.

It is a truism in research that as analysis ventures further from known terrain, the results become less accurate. Each step necessarily introduces new uncertainties. Clearly, our estimates of jet ski noise annoyance are more accurate at the “excess dBA” level of description than at the “dollars” level, since the latter requires two additional assumptions — the dollar value of a beach day to a person (#8 in the list) and its rate of devaluation per excess dBA from jet ski noise (#9). Likewise, the results for a particular beach, for which size, population density, and background noise level are known or can be easily measured, will be more accurate than the results for one of our six beach types, whose parameters are only known statistically.

Least precise, then, are our national results, relying, as they do, on national beach use data and assumptions. This is to be expected. Several years ago, researchers at the University of California of Davis published an entire volume dedicated to calculating the annual cost of all U.S. motor-vehicle noise. They concluded that the cost lay between $140 million and $56 billion — a 400-fold range.(19)

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Of course, the UC Davis analysis encompassed many classes of vehicles, and it considered the full spectrum of noise costs. Still, it suggests that in estimating national noise costs from jet skis, alternative (but still reasonable) assumptions might produce results differing from ours by a factor of two or three. Note, however, that alternate estimates are likely to exceed, rather than undercut, ours, due to the intentional conservatism of our input values.

On the other hand, a very high degree of confidence can be attached to our mitigation analyses, which appear in the next section. These “relative” results estimate the degree to which changes in jet ski usage or noise generation would reduce the overall noise annoyance. They are bound to be more accurate — “robust” in the parlance of policy analysis — than “absolute” results such as noise costs for the entire U.S. or even for a single beach, since any mis-specifications in our assumptions will likely be mutually canceling.

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8. Mitigation Strategies

In this section, we discuss how the noise costs of jet skis to beachgoers might be reduced. We do this by varying several “input parameter” values in the national noise cost model, and observing how the estimated noise cost changes as a result. This sensitivity analysis enables us to gauge the effectiveness of mitigation strategies such as restrictions on usage or engineering changes to new jet skis. Similarly, we can estimate how much, say, jet ski distances from beaches must be increased, to reduce overall jet ski noise costs significantly.

The reader should bear in mind that some steps in the noise cost calculation involve “non-linear” mathematical relationships, as well as random variables. As a result, mitigation strategies generally cannot be assessed by applying simple ratios. For example, the fact that the average noise increment from a jet ski cluster on a popular ocean beach is 7.6 dBA, does not imply that the jet skis would be inaudible if they were made 7.6 dBA quieter. In fact, an average reduction by that amount would eliminate just 63% of the aggregate beachgoer noise impact rather than 100%. Similarly, the reduction in noise from doubling the jet skis’ minimum distance, or even average distance, from shore, cannot be predicted a priori, but must be calculated through the noise cost model.

Here we apply sensitivity analysis to vary three jet ski characteristics: minimum distance from shore, engine noise level, and the number of waterways made off-limits to jet skis. For each, we have determined the changes in these characteristics that would be necessary to reduce by 25%, 50% and 75% today’s $908 million national jet ski noise cost estimated in Section 6. The results are presented in Table 6, for two cases: a “2000” case based on the current (1.3 million) number of jet skis operating in the U.S.; and a “2005” case pegged to the 1.8 million jet skis projected to be operating five years from now.

As Table 6 indicates, to eliminate three-fourths of the nationwide noise cost of jet skis today, either all existing jet skis would need to be made vastly (14 dBA) quieter, or jet skis would have to be barred from 85% of all waterways. For the same result of a 75% reduction in noise costs, but incorporating anticipated growth in usage in 2005, either all jet skis — again, existing as well as new models — would need to be made 16 dBA quieter, or jet skis would have to be barred

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Table 6: Jet Ski Use/Design Changes to Reduce Noise Costs

Base column shows mean values assumed in this report. Other columns show parameter values required for all jet skis, to reduce year-2000 national noise costs by 25%, 50% or 75%. “2000” values assume changes are made “overnight”; “2005” values assume changes are made for the expanded fleet of jet skis in that year. “NA” denotes that the indicated goal cannot be achieved through that strategy. Changes in jet ski characteristics are made one at a time. Combined strategies are shown in Table 7 on p. 48.

from 90% of all waterways. Needless to say, the technical (not to mention political) impossibility of retrofitting the existing 1.3 million jet skis in the United States renders the option of even a moderately quieter jet ski fleet completely infeasible.

The more modest goal of eliminating one-fourth of jet ski noise costs could be reached today either by placing 34% of all waterways off limits, or keeping jet skis at least 450 feet from all shorelines (except to dock, and then only very slowly). Table 6 also shows the stronger measures required to maintain a 25% noise cost reduction in 2005 in the face of growth in the number of jet skis. Either the share of waterways from which jet skis are barred would have to be raised significantly, to 58%, or the distance limit would have to be extended to 1170 feet, between a fifth and a quarter of a mile.

We now discuss these results in detail.

Increase jet ski distance from shore. As noted in Section 5, we assume that jet skis’ distances from shore vary over a wide range, from as little as 50 feet from shore to as much as 2,500 feet for lakes and 10,000 feet for ocean beaches (approximately half a mile and two miles, respectively). In recognition of the common preference of jet skiers to operate relatively close to shore, we constructed our model to assign progressively higher probabilities to smaller distances. The result is that for lake beaches (encompassing lakes, bays, rivers and canals), the average jet ski distance in our model is 530 feet — one-tenth of a mile, or two or three small city blocks; while for ocean beaches

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the average jet ski distance from shore is 1,365 feet, or just over a quarter-mile.

Requiring jet skis to operate far from shore reduces noise costs
to beachgoers only modestly, because sound carries well across water.
A 500-foot limit reduces costs by just 27%, on average.

A number of jurisdictions prohibit jet skis from operating closer to any shoreline than 500 feet (with exceptions for launch access, for which jet skis must be driven slowly, hence less noisily). At best, such ordinances will reduce noise levels to beachgoers only modestly. Sound simply carries too well across water for 500-foot minimum-distance limits to be truly effective.

We estimate that even with perfect compliance — which is by no means assured — a 500-foot rule would reduce noise costs to beachgoers at an average beach by only 27%. Allowing for anticipated growth in usage, if a 500-foot rule was applied universally but as the only mitigation strategy, the national jet ski noise cost in 2005 would be no smaller than today (in fact, we estimate that it would be 1% higher).

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Part of the drawback of a 500-foot rule is that it pushes the average jet ski only 300 feet further out, on average, and therefore attenuates the noise impact on beachgoers only modestly. A more stringent quarter-mile minimum-distance rule, which San Francisco among other municipalities has enacted, has almost twice the noise-reducing effect of a 500-foot rule, reducing beachgoer noise costs by 48% at an average beach. Of course, growth in usage would diminish the effectiveness of this strategy as well; we estimate that under a universal quarter-mile rule, national noise costs in 2005 would be just 28% less than today’s figure, because of an 38% rise in the number of jet skis.

Reduce engine noise. As shown in the middle row of Table 6, national jet ski noise costs would be cut by 22% if it were possible to make an immediate 3 dBA reduction in engine noise emissions from all jet skis — that is, to reduce our estimated average of 80 dBA to 77 dBA (with the jet ski noise level measured “in the water” at 20 feet).

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Further cuts would require steeper drops in noise output. In order to make a significant difference — on the order of 75% — the average base noise level of all jet skis in use would need to be reduced immediately from 80 dBA to 66 dBA. (A 14 dBA drop such as this is equivalent to eliminating 96% of a large number of identical, simultaneous noise sources.) Further reductions of 2-3 dBA would be required to stabilize national noise costs at this sharply reduced level in the face of growth in usage to 2005.

Noise costs are sensitive to jet ski noise level (as measured here from 20 feet,
with jet ski in the water). The evidence is weak at best that new models
are quieter than the 80 dBA mean assumed in this report.

Unfortunately, these figures are completely hypothetical, since there is no possibility that the existing “fleet” of 1.3 million jet skis will be retooled to reduce noise emissions. Any changes to engine designs would affect new models only, which are being sold at a rate of 150,000 a year. At an estimated retirement rate of 50,000 machines per year, it will be half-a-dozen years before the number of present-day machines, with their average 80 dBA noise level, drops below one million.

Of course, new models do present some opportunity to develop and deploy quieter jet skis. Several jet ski manufacturers as well as the industry trade association now tout a number of measures, ranging

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from adding or expanding mufflers, baffles and insulation to redesigning intake and exhaust systems. These design changes, they assert, make new jet skis 50-70 percent quieter than their predecessors,(20) a range of improvements that would nominally correspond to drops in noise levels of up to 8 dBA.

However, the lone new jet ski model for which data were available appears to have a noise level of 83 dBA, or 3 dBA louder than our estimated 80 dBA average for all jet skis now in use.(21) Indeed, with market share rising for higher-horsepower jet skis designed to carry two, three or even four persons, new models may well be no quieter, on average, than our assumed 80 dBA mean for the current fleet.

The most optimistic scenario, then, is that all new jet skis (those put in service in or after 2001) would have in-water emission levels of 75 dBA rather than the 80 dBA average assumed for machines to date. But even with this generous assumption, the national noise costs of jet skis in 2005 would grow to approximately $1.075 billion, a level 18% greater than today’s cost, due to the projected 38% increase in the number of machines in use. Even under a hypothetical “crash” program that doubled the noise suppression gains from new models (to 10 dBA) and also doubled the rate at which they replace noisier older models, jet skis’ nationwide noise costs in 2005 would still be within 8% of year-2000 costs, at $832 million.

This is not to say that engine noise reductions have no value. On average, the noise increment to a typical beachgoer from a 75 dBA jet ski is 35% less than that of an 80 dBA machine. “Source noise” emission reductions of at least 5 dBA should be required for all new jet skis, with further improvements aggressively timed to meet or even force new product development cycles. But such measures should be regarded as only an adjunct to approaches that res