BICYCLING

Bicycling is a simple, affordable, and energy-efficient means of transportation. Of all human-powered locomotion, it is the fastest and least energy-demanding.

The bicycle has stunning efficiency advantages over other vehicles for several reasons:

• It weighs roughly one-fifth of its payload weight. (By comparison, even a small motorcycle weighs more than the rider.)
• With the exception of avid sport and competitive use, it is typically operated at low speeds that do not cause high aerodynamic drag.
• Its internal mechanical efficiency can be nearly perfect —a 1999 test at Johns Hopkins University showed chain efficiencies as high as 98.6 percent — and energy losses due to rolling resistance are far less than for other vehicles.

The light weight and mechanical efficiency not only allow the bicycle to be powered by a nonathletic human, but it can be walked over extreme terrain, or laden with heavy cargo, or picked up and carried. These options make the bicycle more versatile than any other vehicle, and allow a bicycle user door-to-door, on-demand transport.

For any given speed, the energy demands are close to half that of running, and 15 to 20 percent that of ice skating or roller skating. Moreover, better bikes, better techniques, and better athletes continually help set new speed and endurance records. The record speeds accomplished with recumbent two-wheeled bikes enclosed in an aerodynamic shield have surpassed 110 kilometers per hour (68 miles per hour). The record distance that cyclists can cover in an hour on an unfaired (no separate process to make-it more aerodynamic), upright bike has risen from 35 kilometers (21.7 miles) in the 1890s to over 51 kilo-meters (31.7 miles) in the 1990s.

The bicycle's energy efficiency superiority extends beyond human locomotion and beyond all other forms of transportation. By converting food into the energy equivalent of gasoline, the kilocalories of food energy needed by a human to pedal a bicycle is only a fraction of that needed to propel planes, trains, and automobiles (see Table 1).

HISTORY

Bicycles have been around since the early part of the nineteenth century. In 1817 Karl Von Drais invented a walking machine to get around the royal gardens faster. Made entirely of wood, the rider straddled two same-size, in-line wheels, steering with the front wheel and locomoting by pushing against the ground. This steerable hobby horse, which could surpass runners and horse-drawn carriages, never became a viable transportation option because of the need for smooth pathways, which were rare at that time.

A second major effort at self-propelled transportation came when Pierre Michaux invented in 1861 the velocipede ("fast foot") that applied pedals directly to the front wheel. To achieve greater speed with every pedal revolution, designers tried larger and larger front wheels, with some reaching almost two meters in diameter. Despite garnering interest from hobbyists, the velocipede had three major deficiencies as transportation: First, lacking gears, it was difficult to climb even a modest grade; second, because the construction was entirely of wood, with metal tires coming slightly later, the cobblestone roads of the day made for an extremely uncomfortable ride; third, the big front wheel created problems. Riding was extremely dangerous and inaccessible to most women and children.

A fresh start and the true beginning of bicycles becoming a popular means of transportation can be traced to around 1886 and the efforts of John Kemp Starley and William Sutton. With equal-sized wheels, tubular steel diamond-shaped frame geometry, and a chain-and-sprocket chain drive to the rear wheel, the "safety bike" looked much like the modern version.

During the late 1890s, bicycles were the worldwide focus of invention and technical innovation, much as biotech engineering and computers are today. We owe many of today's industrial manufacturing processes, designs for bearings, axles, and gearing mechanisms, and the knowledge of lightweight structures, to the explosion of inventions that bicycles produced.

In the United States, England, and other major nations, patents were awarded at the rate of about 5,000 per year per nation. In one peak year, bicycle-related patents comprised close to one-third of all patent-writing activity. Many of these patents were decades ahead of the technology to manufacture them; for example, suspension systems invented a century ago became viable only with modern-day elastic materials and manufacturing technology.

The two most important single inventions of this long-ago era were Starley's tension-spoked wheel and John Dunlop's pneumatic tire. The tension-spoked wheel was and is a marvel of lightweight structures; it allows four ounces of spokes, on a wheel weighing a total of three or four pounds, to support a 200-pound rider. (Today's carbon fiber wheels have yet to show a clear advantage over the wheel made from humble carbon steel spokes.) The pneumatic tire, which Dunlop invented in 1888, vastly improved the bike's comfort, and it also shielded the lightweight working mechanisms from excess vibration and fatigue. The coaster brake appeared in 1889, and it has been a staple of children's bikes ever since.

Because a bicycle uses a low-power engine (the rider) and because that rider can only apply power only over a small rpm range, gearing is essential to match the rider's output to the riding conditions. The first patent for bicycle gears was granted in France in 1868; the rider pedaled forward for one gear and backward for the other gear.

An 1869 patent by France's Barberon and Meunier foresaw today's derailleurs. It described a mechanism that would shift a belt or chain sideways among three sprockets or discs. That same year, Barberon and Meunier also patented a primitive gear hub.

These technical innovations dramatically improved performance. Bicycles of that era were hand-made in cottage industries, and were highly sought after and expensive. So impassioned were their owners that the League of American Wheelmen, founded in 1880, was for several years around the turn of the century the strongest political lobby in the United States, with a membership in the hundreds of thousands. The League's "Good Roads Movement" was the first political movement to lobby for a network of high-quality, paved roads throughout the nation.

Between the development of the chain-drive bicycle in the 1880s, and before Henry Ford popularized the automobile in the 1910s and 1920s, bicycling was extremely popular as an efficient means to quickly get around. It was over three times as fast as walking, and more convenient and cheaper than having a horse-drawn carriage at one's disposal. Unfortunately, the quickly improving performance, reliability and affordability of the automobile made it a formidable competitor to the bicycle.

The automobile ascended to dominance in North America starting in the 1920s, and in Europe by the 1950s. After World War II, most nonauto ground transport in the United States rapidly disappeared. The decades following World War II saw vast reductions in train travel, bus service, and public transportation systems in major cities.

The shift to personal autos was slower in many European countries, where many of the population could not afford autos, and where the governments placed very high taxes on gasoline and automobiles. Bicycles, motorcycles and public transportation continued to be widely used in these countries. In addition to the economic factor, there was a cultural reason for Europe's slower embrace of the automobile. Europeans have long lived with high population density within finite borders. The United States of the 1940s was a far more rural nation, with sprawling farmland inside the borders of major cities. That autos took up lots of space in a city was an obvious drawback to the European mind, but irrelevant in Texas.

The poorer nations of the planet had no choice, and used bicycles and public transportation exclusively. For example, when China was under Mao Tse Tung's rule, the number of private automobiles was only in the hundreds.

Beginning in the 1970s, the bicycle saw a resurgence of interest in North America. Reasons included environmental concerns with the internal combustion engine, the popularity of bicycling as a multifaceted sport (racing, touring, mountain-bike riding, family cycling), the desire for fitness, and the need for alternative ways of commuting in crowded cities.

Bicycling to work is viewed as the most environmentally friendly means of travel, the best way to avoid congested roadways (in some cases, it turns out to be quicker than mass transit or driving), and a means of turning commuting time to exercise time. The bicycle is far more efficient than the automobile in making good use of city streets. Traffic counts taken during the 1980 New York City transit strike showed that a single street lane devoted to bicycles could carry six to eight times the number of people per hour than as a lane for auto traffic.

During these past few decades, the bicycle itself has vastly improved. The bicycles of the early 1970s usually had mechanical idiosyncrasies. Competition among manufacturers, led by the Japanese companies that entered the U.S. market, resulted in vastly improved quality control. The mountain bike, first made available on a widespread basis in 1983, offered a delightful alternative that mushroomed in popularity, and a decade later, traditional "road" bicycles had all but disappeared from stores. The mountain bike has become most people's vehicle of choice for city riding as well as recreational trail riding.

It has also helped that the bicycle buyer is continually offered more bicycle for less money. No longer are most bikes steel. While steel continues to be a fine material, the dominant material reported by bike enthusiast is now aluminum, which, in the hands of most designers, yields a lighter but more rigid frame. Well-heeled bicyclists opt for titanium or carbon-fiber composites.

There has also been a huge improvement in the value of today's mountain bikes. A mountain bike in the $300 to $500 price range typically has a suspension fork and aluminum frame that would have made it a $1,500 bike a decade earlier. The $800 dual-suspension bike of 2000 far outclasses the early 1990s $2,500 offering.

THE HUMAN ENGINE

The bicycle's advantages as the world's most mechanically efficient means of transportation are clouded by the limitations of the human engine. To put it in power output terms, the human body can produce sustained power only at modest levels. For most people, 100 watts would be too much, and for an elite athlete, 400 watts is the approximate ceiling. (The athlete may manage a brief burst of 1.1 kilowatts.)

The lower power output is inevitable because a body cannot long produce more power than it can simultaneously convert from the chemical mixing of blood glucose and oxygen (aerobic exercise). The higher brief bursts of power do not rely on real-time glucose/oxygen consumption, which is why the athlete is out of breath for minutes afterwards. The athlete's muscles have "borrowed" the results of future oxygen and glucose consumption in anaerobic exercise. For long-distance travel, yet another limitation appears: the body stores about a two-hour supply of glucose. After that glucose is exhausted, the body has to revert to the far less desirable mechanism of burning fat. The muscles produce less power with fat than they do with glucose, and only a trained endurance athlete can comfortably exercise beyond the glucose barrier into the fat-burning zone.

When the automobile became preeminent in the early twentieth century, it did so with good reason. Whether the energy to power a bicycle is anaerobic or aerobic in nature, it is still minuscule in comparison to what an automobile's internal combustion engine can deliver. In the United States, almost all subcompact cars are equipped with engines that can generate 100 or more horsepower (74,600 watts), and can sustain this output all day long.

The human engine cannot match this power output, yet the mechanical efficiency of the bicycle helps tremendously because a very small amount of horsepower can generate great speed. For example, 0.4 horsepower (298 watts) of output can result in 25 mph (40 kph) speeds or better. One set of calculations shows that if a cyclist rode on level ground, with no rolling resistance, and aided by a 25 mph tailwind, it would require only around 0.2 horsepower (150 watts) to sustain a 25 mph pace.

Gravitational Resistance

If not for the need to climb steep hills, bicycling at a 15 mph (24 kph) clip would never be a strenuous exercise. It takes approximately 82 watts, or 0.11 horsepower, on an efficient bicycle, to ride 15 mph on flat ground. But ground is seldom flat. That same 82 watts achieves only 8 mph climbing a barely discernible two percent grade. A five percent grade slows one down to just over 4 mph. Most riders don't want to slow down that much, so they work harder to maintain some speed. On descents, they work less hard, while going still faster.

Any weight reduction helps. Gravitational forces do not discriminate between bike and rider mass, but the human body does. If one spends an extra thousand dollars to shave ten pounds off a bike, there will be a 10-pound advantage, but if one sheds the 10 pounds from the belly, the body will not have to nurture those ten pounds of living tissue, and one will be a more efficient engine.

Air Resistance

Air resistance is a greater factor than most people realize. Even at 10 mph on flat ground, almost half the rider's energy goes to overcoming wind resistance. Rolling resistance is almost nil at the speed. At 15 mph, two thirds of the energy is need to overcome wind resistance. At 25 mph, about 85 percent of the rider's energy is devoted to overcoming wind resistance, with the remainder overcoming rolling resistance and the tiny frictional losses within the bicycle itself. So sensitive is the wind resistance to the rider's aerodynamic profile that riders who race time trials at these speeds feel the bike slow down dramatically if they sit up to take a drink from their water bottles.

For these reasons, most riders cannot, or will not, increase their speed much above their personal comfort levels, even with lots of training. The additional speed just costs the rider too much energy. A rider going 15 mph must double his power output to ride 20 mph. Why these dramatic numbers? Wind resistance varies with the square of the rider's airspeed, but the energy to overcome wind resistance increases with the cube of the rider's airspeed.

Of course, the air is rarely still, just as the ground is rarely flat. Tailwinds do speed the rider, but headwinds have a direct effect on the rider's speed, too: A rider traveling at 20 mph into a 15 mph (24 kph) headwind encounters as much air resistance as a rider traveling at 35 mph (56 kph) under windless conditions. A headwind will slow one down by half its own speed. If one normally rides 15 mph, and then steers into a 10 mph headwind, the resulting speed will be 10 mph.

Because of the significant increase in drag a rider encounters as speed is increased, small adjustments of bike and body contours can significantly alter energy expenditures. These alterations can be to clothing, frame design, handlebars, wheels (spokes), rider profile, and the race strategy of drafting. Of the two resistance factors, the rider and the bike, the rider accounts for approximately 70 percent of the wind resistance encountered, while the bicycle accounts for only 30 percent. Unlike a sleek automobile, the high upright bike and rider is a very inefficient aerodynamic profile, so encircling a rider and bike fully or partially in a streamlined fairing can drop the drag coefficient by 0.25, resulting in a top speed increase from 30 to 36 mph (48 to 58 kph). However, this gain could be somewhat negated on hot days because of the body overheating, or from instability caused by gusty crosswinds.

Fully faired bicycles and faired adult tricycles are today the stuff of cutting edge inventors and hobbyists. Virtually all of them are recumbent bikes, because it makes sense to start out with a smaller frontal area to begin with. Some are reasonably practical for daily use, with lights, radios and ventilation systems; others are pure race machines.

Rolling Resistance

Rolling resistance is almost directly proportional to the total weight on the tires. It is the sum of the deformation of the wheel, tire, and road surface at the point of contact. Energy loss occurs when the three do not return all of the energy to the cycle.

Rolling resistance varies tremendously by tire. Greater air pressure and less contact area is the reason the rolling resistance that a tops of-the-line racing tire encounters on smooth pavement is half or one-third that of a heavily-knobbed mountain bike tire.

But unlike air resistance, rolling resistance varies directly with speed, which means that as speed increases, the rolling resistance factor becomes less important relative to the air resistance. A bike going 20 mph has twice the rolling resistance of a bike going 10 mph. If the bike has good-quality tires with proper inflation pressure, neither rolling resistance number is high enough to be particularly significant.

Rolling resistance declines with smoother and harder road surfaces, larger diameter wheels, higher tire pressures, smoother and thinner tread, and narrower tires. In the case of rough, pot-holed roads, energy is lost in bounce. For soft surfaces such as gravel or sand, energy is robbed and absorbed by the surface. Anyone who has ridden with severely under-inflated tires or through mud can attest to the extremely wasteful loss of human energy.

Over rough surfaces, an opposite effect, not easily measured in the laboratory, becomes apparent to the rider. A tire inflated to very high pressures (for example, 120 pounds) bounces off the peaks of the road surface, making the bike harder to control, and negating any theoretical decrease in rolling resistance. For that reason, top racers often use moderate inflation pressures (85 to 90 pounds). Studies have found that superinflatable tires (120 to 140 pounds) offer no noticeable advantage over high-inflation tires because they do not appreciably decrease rolling resistance.

Wheel size can have as dramatic an effect on rolling resistance as tire inflation. On paper, a smaller wheel size has more rolling resistance, a rougher ride, and poorer handling over bumps than a larger wheel size. Rolling resistance is inversely proportional to the radius of the cylinder, that is, given the same conditions, smaller-wheel bikes experience more resistance to motion than larger-wheel bikes.

Fortunately for the makers of small-wheel folding bikes, several factors can mitigate these shortcomings, such as by using wider tires to compensate for the smaller diameter. The use of improved modern tire technology and the use of suspension in combination with small wheels also help. In modern times, the father of small-wheel suspension bikes, Alex Moulton, began designing these bikes in the 1950s, and his most recent designs have taken this bicycle type to a new level. Hot on the heels of the Moulton bicycle are bicycles such as Germany's sophisticated dual-suspension Birde. Many riders believe these bikes completely negate the alleged disadvantages of small-diameter wheels.

Pedal Cadence

Numerous physiological studies have addressed the optimum pedal cadence, but these studies usually miss the point because they focus on the seemingly important factor of efficiency.

Efficiency is measured in power output per oxygen consumed. However, the rider's supply of oxygen is, for all practical purposes, unlimited, and most riders do not pedal at an effort level that leaves them constantly breathless. Even if they did, they would not want to follow the results of efficiency studies. These studies consistently show that recreational cyclists produce the best sustained performances (lowest metabolic rate and highest efficiency) when the seat is raised 4 or 5 centimeters above the normal height, the pedal cranks are slightly longer to make it possible to use higher gears, and the pedal cadence is in the 40 to 70 rpm range. However, experienced riders, whether fast or slow, virtually always choose to ride differently than the studies recommend.

Why? Efficiency does not matter if one has unlimited oxygen. What does matter is long-term comfort. Pedaling at the rate shown to be most efficient uses up blood glucose the fastest. This leaves the rider more susceptible to that sudden loss of energy known as "the bonk," and it also tends to leave more lactic acid and other waste products in the muscles, increasing discomfort and extending recovery time.

By contrast, pedaling faster (90 to 100 rpm) in a lower gear at a lower effort level allows the body to burn some fat along with the glucose, thereby extending the glucose reserves. The more rapid leg motion promotes blood circulation, the better to remove waste products from the muscles. This faster cadence is undeniably less efficient, because the body uses energy just to spin the legs around, but it results in increased long-term comfort.

Novice cyclists will often prefer the "more efficient" slower cadence and higher saddle because this configuration uses the leg muscles in a manner more similar to the way walking uses those muscles. In addition, the novice cyclist is often unable to benefit from a higher pedal cadence because of an inability to apply force perpendicular to the crank, resulting in excessive body motion. A bike rider needs to gain some experience with the "less efficient" faster cadence so his/her muscles develop the coordination to function smoothly in this new discipline. Having done that, the rider is unlikely to go back to the slower, less efficient way.

Cleated shoes and toeclips are also advocated on efficiency grounds. Every world-class cyclist uses toeclips today because studies have shown significant aerobic and anaerobic benefits. Toe clips often give elite riders a false sense of power production during the stroke recovery phase. Elite riders feel that toeclips double their deliverable pedal power —a coordinated push-pull effort, exerting an upward force, with the trailing leg alongside the downward force of the forward leg. In reality, however, the cadence is too fast to create a pulling-up force. The importance of cleated shoes and toe clips is in their ability to stabilize the foot and more effectively generate a pushing force rather than in generating a pulling force during the recovery stage. Recreational cyclists benefit from this foot stabilization as much as elite cyclists, do but many of them are uncomfortable with toe clips. Moreover, toe clips are undeniably clumsy in the frequent start/stop environment of crowded city traffic.

Alternative Propulsion Systems

Throughout the history of the bicycle, inventors have questioned whether the century-old circular sprocket design is the most efficient. Many inventors have built elliptical chainwheels, usually to have a "higher gear" during the power stroke and a "lower gear" during the dead spots at the very top and bottom of the pedal stroke. Numerous studies show that even elite riders are unable to apply propulsive force to the pedals during these portions of the power stroke, much as they are unable to lift on the backside of the power stroke.

These elliptical chainwheels have never been widely popular. Sophisticated cyclists tend to shun them because cyclist develop a riding rhythm and a comfort pattern from years of experience. Novices do not even know they exist. Most bike designers fear that elliptical chainwheels would tend to make novice cyclists less inclined to develop a smooth pedaling style.

During the 1980s, Japan's Shimano Corporation invented a radically different alternative to round chainwheels. The development of Shimano Biopace chainwheels began with a very sophisticated study of the biomechanical performance of bicyclists, and Shimano discovered two flaws that it wanted to correct. The first flaw was that the leg was speeding downward as the foot approached the 6 o'clock (bottom) position, and this downward momentum of the leg mass was not being harnessed and converted into forward motion. The second flaw occured during the upstroke phase of the pedal path. Shimano discovered that at this point in the pedal path, the knee joint was switching from flexion to extension, and the switch was so fast that both sets of muscles were being energized at once —so that the body was fighting itself.

Shimano addressed the first problem with a design that seemed counterintuitive. The chainwheel was shaped so that the rider experienced the feeling of a lower gear during the power stroke. Then, at the bottom of the pedal stroke, the gear got higher, to absorb the energy from the leg mass's downward momentum (see Figure 1). The second problem was addressed by a change in the chainwheel shape, which slowed down that portion of the pedal stroke, giving the leg a few additional hundredths of a second to switch between flexion and extension.

As good as Shimano's research was, the product bombed in the notoriously conservative bicycle marketplace, and Biopace is history today. It's doubtful that bicycles will ever come with nonround chain-wheels. The round ones do too good a job, and are too easy to make and market.

Lever propulsion —requiring an up-and-down stair-climbing motion —is another propulsion system long proposed, on efficiency grounds, as a replacement for the standard pedal-and-crank system. Though promising in theory, studies have shown that the muscle efficiency for pedaling a chain wheel is not inferior to that associated with stepping and steep-grade walking. Lever systems maximize the problem of harnessing the leg mass's downward momentum, and work against the smoothness that experienced riders have come to enjoy so much.

There is no basis for the theory that only when pushing the whole stroke vertically do the muscles work efficiently, and that the backward-and-forward foot movement over the top and bottom wastes energy. Certainly, there is some efficiency loss, but it is minimal. Toe clips and better variable gear systems have further minimized "top-dead-center problems" associated with the standard circular sprocket design.

THE BICYCLE AS TRANSPORTATION

Bicycles are the number-one mode of transportation in the world. More than 100 million new bicycles enter the market each year and, in Southeast Asia alone, around 700 million bicycles are used daily as a means of transportation.

China is the world's biggest producer and user of bicycles. Since 1985, China has been manufacturing more than 30 million bicycles each year. In Shanghai, more than 4 million people bicycle to work and school every day. Bicycles far outnumber automobiles. Whereas there is one automobile for every 1.7 people in the United States, in China there is only about one automobile for every 680 people. However, the developing nations seem determined to become overdependent on the automobile as well. In the quest for greater status and mobility, motorized vehicles are quickly becoming the most sought-after possessions in Asia and other developing nations. This pro-auto movement quickens with economic growth that creates more capital to purchase the vehicles. Paying for the energy to run the vehicle is a much smaller concern. As a larger segment of the Asian population rapidly becomes affluent and develops an addiction to the automobile —similar to that is the United States and other developed nations — world petroleum consumption will soar. The U.S. Department of Energy projects Asian transportation petroleum demand will nearly triple from 1995 to 2020, going from 9.6 to 26 quadrillion Btu's.

Although the bicycle is primarily used for recreation in North America, some urban areas (e.g., San Francisco, New York, and Toronto) are experiencing an upswing in the number of workers commuting by bicycle instead of car. Widespread use of bicycles for commuting would have a profound effect on energy supplies and society. If half of the U.S. labor force biked to work instead of driving, the United States could significantly curtail petroleum imports; moreover, the exercise attained by pedaling to work could shrink the obesity and overweight population, and thereby dramatically improve the overall health of many. Despite these benefits, a massive switch to bicycling is highly unlikely for one major reason: It is impractical. There are too many inconveniences involved that are simply unacceptable to the majority of an increasingly affluent population, particularly when the alternative is a climate-controlled, high-speed drive to work in a very comfortable automobile.

The primary inconvenience is the relative slowness and lack of comfort, especially during days of inclement weather. Many millions of Americans live great distances from where they work. Some might consider bicycling five miles to work each day, but few live that near to work. The typical 20-or-30-mile commute makes bicycling an unrealistic option for most people. And for those who do live close to work, few are willing to brave the elements to bicycle year around. Rain, snow, ice, high winds, extreme cold, and extreme heat that are minor inconveniences in a vehicle become major inconveniences on a bicycle. Thus, for backup, bicycle riders usually must own a vehicle for bad weather days, or have access to convenient mass transit.

By contrast, the bicycle survives as basic transportation in the Netherlands and Germany because those nations have a social infrastructure built to make it possible. Those countries have a neighbor-hood-centered way of life, and the trip distances on a bicycle are often two or three kilometers or less. People cycle slowly out of politeness to others on the crowded streets. Public transit is also far better than in the United States. It is amusing to see a German commuter train station with virtually no auto parking available, but hundreds of bike parking spots.

Intermodal commuting with a bicycle may someday be a way around congested roadways. One of the biggest problems facing mass transit developers is trying to provide service to a sprawling, residential community that needs to commute to equally decentralized work sites. The majority of the population resides a driving distance from mass transit stops, and mass transit service ends too far from a work site to make walking practical. If buses and trains were equipped to carry bicycles, or folding bicycles gained wider acceptance, the bicycle might someday serve as the intermodal link. The bike could be pedaled to the train, loaded for mass transit, and then pedaled the final leg of the commute. It is uncertain whether this alternative means of commuting will ever become attractive enought to overcome the drawbacks of weather, bicycle storage, and safety concerns.

Some people believe that bicyclists require dedicated bike lanes and trails. This is a half-truth. Certainly, these facilities are widespread in Germany and the Netherlands, but they are far less common in other cycling countries such as the United Kingdom, France, and Cuba. In those countries, bicyclists have long known that they can share the road with automobiles as long as all road users respect the same set of rules.

Dedicated facilities are often cited for safety purposes, but this, too, is not a simple truth. Most accidents occur at intersections, and dedicated facilities make intersections far more complex. When the Netherlands allowed their moped riders to travel in the auto lanes instead of the bike lanes, the moped accident rate fell by an astounding 70 percent. The bicycle accident rate would be higher if bicyclists tried to ride at brisk speed in these separated bike lanes. The sub-10-mph speeds that are considered polite in these countries largely allow bicyclists to compensate for the facilities' shortcomings, at the expense of travel time.

In the United States, advocates for bicycling are divided on the question of special facilities. It is doubtful that Dutch-style facilities would create much greater ridership in most U.S. locales, because the trip distances are too long. The best reading of accident statistics shows that adult riders well-schooled in sharing the road with automobiles and respecting the same rules ("vehicular cycling") have about one-fifth the accident rate of a control group of otherwise-well-educated adults.

Aside from the comfort and convenience disadvantages of bicycling, perhaps the biggest obstacle is the price of energy. Energy is far too cheap to make pedal power worthwhile, except as a hobby. For most people, the cost of the one or two gallons of gasoline used commuting each day is paid for in less than 10 minutes of work time. Of course, the pedal power equivalent of electrical energy is even less. To travel at 15 mph (24 kph) on flat ground requires only around 82 watts of power. If one ran on electrical energy instead of food energy, the cost of the electricity to generate that 82 watts to travel 14 miles to work is about 0.7 cent.

Sweating is another problem. Few people want to arrive at work with a sweat-soaked body. There are usually no showers at work, and few want the additional burden of lugging work clothes that would need pressing on arrival. For most riders, sweating is inevitable, particularly when climbing hills. The human body is about one-third efficient in converting the energy of glucose into muscle movement. The other two-thirds is waste heat, and sweat is how the body gets rid of excess heat.

Because of the desire to avoid perspiring, and the limited energy available to propel a bicycle, there is growing interest in electric motor-assisted bicycles that can make that 15-mile commute to work a near-effortless experience. The electric motor allows the rider to maintain a reasonable speed without exerting enough energy to perspire. The U.S. market saw at least a dozen brands of electric-assist bicycle during the 1990s. The more sophisticated offer regenerative braking 15 to 20 miles of range, and recharging cost of 2 to 3 cents for a 15-mile distance (at 10 cents kWh).

These bikes could be a wonderful transportation option, combining the efficiency, quiet and nonpollution of a bicycle with the ease of riding a small motorcycle. For these reasons, electric-assist bikes sell at the rate of over 200,000 per year in Japan. But in the United States, these bikes run up against a cultural barrier. Bicycle enthusiasts, who are less likely to object to their four-figure price tags, do not want a motor and do not want a bike that weighs 60 pounds. Others do not want to be seen riding to work. So U.S. sales have been poor. As the number of motor scooters and motorcycles in Asia has grown at an alarming rate, policies to encourage the use of electricity-assisted bicycles are seriously being considered as a way to curtail vehicle emissions. In Bangkok, Thailand alone, over one million people needed treatment for smog-related respiratory problems in 1990. Greater affluence and the demand for faster transportation in China have resulted in yearly sales of motorcycles increasing from less than half a million sold in 1991 to over 10 million by 1996, further contributing to air pollution that is already some of the worst in the world. Unless zero-emission transportation, such as electric bicycles, gains in popularity, the number and severity of smog-related respiratory problems are certain to worsen in the most densely populated urban areas of Asia.

John Schubert John Zunerchik

See also: Aerodynamics; Biological Energy Use, Cellular Processes of; Culture and Energy Usage; Flywheels.

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