The impact of discovery and invention on society is usually unknown for years and sometimes decades and most have little impact, but a handful have led to fundamental change. Some; the electric grid, safety elevator, air conditioning, automobile, airplane, electric water pump - to make a partial list - have brought about change that can easily be observed from low Earth orbit.
The automobile is an interesting case. The first real expansion of a technology that had been evolving for nearly a century began around WWI, but was limited by high costs and an undeveloped road and support infrastructure. This began to change dramatically in the twenties and by the end of WWII most families could afford to own and operate at least a used car and the expansion of roads had reached a point where most people could easily travel between where they lived, worked, shopped and played.
Most people justify about an hour's worth of daily commuting two and from work. The automobile had increased the average commute distance from a few miles to something ten to twenty times greater. The range of the average person was now greater than the size of most towns. Cheap land and new houses in the fifties and sixties created suburbs around most cities.
At this point something around one and a half percent of the lower 48 states are covered with asphalt and concrete surfaces devoted to transportation. Some negative aspects of burning hydrocarbons are threatening the environment, petroleum is becoming more expensive with the trend likely to continue, and the cost of operating a car is about sixteen percent of the average families total cost of living - only housing is greater. Congestion in many areas caused a lot of daydreaming about how to get around the traffic jams that began to appear around the major cities. Fixes like personal helicopters and monorails were proposed in the futurist magazines of the day, but no real solutions have been implemented here.
At some point you have to ask the question “how efficient is our transportation system?” Probing a bit consider a bit more than forty percent of trips in the US are under three miles long, a third are under two miles, and a fifth are under a mile. Cars seem ill-matched to journeys of this length, but for anything over a mile walking is probably going to be too slow and point to point public transit in most parts of the country is non-existent.
Something like a bicycle makes a lot of sense for short trips assuming a few social problems can be solved.
It turns out a human and a bike offers an efficiency roughly equivalent to one thousand miles per gallon ...
Energy and power (power is just the energy you use divided by the time it takes to use it) have any number of units, but to physics energy is just energy. It can’t be created or destroyed - just moved from one from to another. If you are riding a bike fusion deep in the Sun's core ultimately produces light that travels to Earth and is converted into food by photosynthesis. We eat plants directly or animals that eat plants, but basically we’re solar powered. A similar path is mostly true for a car - photosynthesis creates biomass that is stored and heated for a long time underground to produce petroleum. (mostly as there are some counterexamples like electric cars that get their energy from geothermal or nuclear sources, but those are currently rare).
Not going into depth, but just noting that photosynthesis is very inefficient - usually under one percent of the energy falling on a green plant is transformed into stored chemical energy (food). Fortunately the area under cultivation on our little planet is large enough to deal with our current population. The process of making petroleum is even more inefficient, but it is done over millions of years which has given us enough for the past hundred years. Unfortunately the creation of hydrocarbon fossil fuels is glacially slow. We are currently burning them at ten to one hundred thousands times as fast as they are being created, so they are non-renewable and as such have some other nasty properties.
Nasty properties aside, gasoline and diesel fuel - liquid hydrocarbons - are excellent energy stores. They are reasonably safe and easy to handle, relatively inexpensive (that is changing), and have a high energy density. There are sound physical reasons why their discovery and use proved to be revolutionary. Without liquid hydrocarbons the development of the automobile would have been radically different and we are only now developing technologies that allow for ballpark similar performance.
To look at how many effective miles per gallon a person can get on a bike we need to know something about the fuel being burned and how much energy it takes to move the bike and rider over a known distance.
Properly measuring a bike rider isn’t trivial. You can look up carefully measured figures and make some adjustments for an approximation or you can do the measurements yourself. Having access to a low speed wind tunnel and some serious measurement kit comes in handy.
I’ve done this for Colleen. Riding in a comfortable upright position her tall frame isn’t exactly aerodynamic, but remember that the power needed to cut through the air goes up as the cube of the speed - at slow speeds being aerodynamically “dirty” isn’t a big thing. If she wanted to decrease her drag, she could bend over to present a bit less surface area.
a bit of high school physics:
At 22.5 kilometers per hour she needs about 80.6 kilojoules to cruise along for a kilometer.1 In units more people may recognize this is about 14 miles per hour and 31 food Calories per mile. She is burning something like 434 Calories over her basic needs to cycle for an hour.
It is interesting to calculate the power she is getting from the metabolism of her food at this steady pace. In an hour she requires about 1814 kilojoules of energy, so dividing by the seconds in an hour we get a bit more than 500 watts. Not all this food energy is being converted into useful mechanical work. It turns out many of the muscle movements we make have efficiencies around twenty percent (some are much lower, others a bit higher - if your exercise equipment reports Calories burned, it is probably integrating power over time and multiplying by about 5). Colleen happens to be a trained athlete with wonderfully smooth motions and is a bit over twenty percent efficient on a bike.
In other words she is delivering about 100 watts of power to the crank.
One hundred watts is an interesting result for a human. An average person might eat about 2000 Calories per day. To make the arithmetic a bit easier assume it is 2064 Calories per day. Converting to watt-hours we get 2400 watt-hours per day. Divide by 24 hours in a day to find the average power- an average person gets about one hundred watts from her metabolism.
Much of this - around eighty percent - is given off as heat and you can warm a cold room by having a few dozen good friends over for a party.
You can approximate the power requirement of a person as being the same as that of a 100 watt light bulb.
Increasing physical effort requires more energy. Experimenters a few hundred years ago found an average man in good physical shape can produce about one hundred watts of power, over and above his basic needs, for an eight to ten hour period. Farm hands doing mechanical work can eat a lot of food. So do athletes, When Colleen was in training she required five to six thousand Calories per day and remained thin. (note - her basic needs are somewhat above 100 watts as her body isn't exactly average)
A bit of arithmetic shows 30 miles per gallon of gasoline is about 2750 kilojoules per kilometer. The car uses about 34.1 times the energy Colleen does to travel the same distance.
Colleen is getting close to 1025 miles per gallon - if she is drinking a vegetable oil. That doesn’t work for her so you can figure out what she gets on a gallon of Ben & Jerry’s if you like.
You can probably get a similar result and there are tricks, aerodynamic and otherwise, to improve it.
Still - a thousand miles per gallon is an impressive figure. A bike rolls easily, has a very efficient transmission, doesn’t have a lot of wind resistance at low speeds, and - most important - is much lighter than the rider rather than a few dozen times heavier. At normal cruising speeds it is one of the most efficient ways for a person to get around (about three times as efficient as walking). A three mile trip requires less than fifteen minutes which may be short enough to be practical for many of us. In theory bikes could be used for about forty percent of trips in the US .. but only in theory.
The problem is making bikes practical. Bikes need to be perceived as “safe enough” which makes demands on roadways and motorists. The bike needs to be available when you need it. It must be socially acceptable to ride and so on...
In the mid seventies a few Northern European countries took very different paths from the US and each other to reduce car use and increase “active” transportation (biking and walking). Their solutions vary and are very much a systems approach, but cycling has become socially acceptable in these and participation is extremely high by American standards (some cities see more than half of trips under five kilometers being taken on foot or bikes).
Some of the problems caused by cars are being reduced. There are lower demands on the area required for parking and roads, noise and air pollution has dropped, the average family outlay for transportation is lower than in the US (even though gasoline is regularly over $9 a gallon now), and there is a correlation with improved health.
Improved health may be the greatest benefit and it was not predicted. It turns out people seem to require at least a half hour of aerobic exercise per day to stay healthy - some suggest the number is more like an hour. Children require more. Americans have become extremely sedentary and often find it difficult to find time or motivation for exercise. Cycling is excellent exercise and a visit to Amsterdam or Copenhagen shows a population with much less obesity than in the US. Jheri, a friend in Copenhagen, notes Danish women have the best butts and legs in the world and it is all from biking...
This just scratches the surface. How these countries evolved and met obstacles is fascinating. Matching transportation to time and distance in the US is not optimized and moving towards something better may well be socially impossible, but interesting things are happening in a few cities.
On the longer term there is the a new challenge of what a car is and how the landscape and people will change with it. Megacity cars are likely to be a radical departure from what we know today. It will be interesting to see if they come in time to change the landscape of China, India and countries that are only now emerging economically.
Some city and megacity solutions have been tried and failed as the social impact was not considered. The Segway was an interesting case. Imagine taking a light weight low speed vehicle and putting an electric motor on it, the intention being to increase the range of walking by a factor of three or four. After all - human muscles turn energy into motion at about twenty percent efficiency, but a small electric motor can exceed eighty percent.
In theory the Segway would be a nice way to get around a city, but in practice the user experience felt much to be desired. They are too bulky and heavy to easily move around wherever you go, expensive, too fast for safe integration with pedestrian lanes and too slow for normal roadways and so on. Many of the same points can be made for bicycles, but the Segway has its own some set that need to be addressed. But perhaps most important is something an anthropologist friend said to me the day the Segway was announced:
people will never go for them as the riding posture makes you look stupid
She nailed it (I've come to consult with and trust anthropologists for many issues associated with the acceptance of new technologies). But it raises the question of why cars are often viewed as objects of desire - often going beyond their utilitarian nature. How and when did the car become romanticized?
The question is clearly complex but there are fascinating hints. Studying the history of advertising, one comes across references to Ned Jordan - a reporter who became involved in the auto industry forming the Jordan Motor Car Company in Cleveland in 1918.
Folklore has it that he saw a beautiful woman racing her horse by the train on a trip through Wyoming. He asked the conductor where they were and heard: Oh, somewhere west of Laramie. He penned an ad for the Jordan Playboy which was published in The Saturday Evening Post. I seen it cited as a watershed moment for associating a product with romance rather than the product itself.
... the text of the ad (if it is difficult to read)
Somewhere west of Laramie there’s a broncho-busting, steer-roping girl who knows what I’m talking about.
She can tell what a sassy pony, that’s a cross between greased lightning and the place where it hits, can do with eleven hundred pounds of steel and action when he’s going high, wide and handsome.
The truth is--the Playboy was built for her.
Built for the lass whose face is brown with the sun when the day is done of revel and romp and race.
She loves the cross of the wild and the tame.
There’s a savor of links about that car--of laughter and lilt and light--a hint of old loves--and saddle and quirt. It’s a brawny thing--yet a graceful thing for the sweep o’ the Avenue.
Step into the Playboy when the hour grows dull with things gone dead and stale.
Then start for the land of real living with the spirit of the lass who rides, lean and rangy, into the red horizon of a Wyoming twilight.
The copy and illustration are in stark contrast with other ads of the period.
And that, Virginia, is how they sell SUVs... (and everything else)
In Copenhagen and a few other cities there are efforts to show biking commuting as normal, cool, and even sexy - anything but pure recreation and sport. Riders in street clothing rather than lycra on mostly non-exotic bikes and an upright riding position. Safety is built into the behavior of drivers - for example when a Danish or Dutch driver opens a car door she is taught to do it with her right hand. This forces her to swivel her head and watch for close bike traffic so she won't accidentally "door" someone. The legal system assumes a driver is at fault in a bike-car collision (and a bike in a bike-pedestian collision), unless proven othrewise. There are dozens of differences like this that have become part of the culture in the last two decades.
It would be fascinating to understand the differences in attitudes and towards different types of transportation as a function of country and culture....
1 Approximations for calculating bicycle energy use range from about 1 to 1.6 kJ/(km-kg) and depend on bike speed, terrain and traffic, assumptions of the rider's efficiency and cadence, assumptions about the bike's efficiency, and aerodynamics. Most of the measurements have been conducted at slightly higher speeds and some have assumptions about normal use (how many starts and stops per hour) built-in. While Colleen's figure presents a relatively large surface area due to her height and riding position; the speed is somewhat lower, the tires are low resistance, the terrain flat and the measurement is at a constant speed. She also happens to be an athlete with a smooth and efficient motion.
Walking is generally around 4 kJ/(kg-km) at optimal cadence. Cycling and walking are both very sensitive to cadence and surprisingly, long legs are not an advantage and in the case of walking are as important as many assume in determining optimal walking speed. Efficiency drops dramatically if you are off cadence on a bike and are off optimal speed walking.
The most efficient swimming strokes require about 17 kJ/(kg-km) - distance swimming requires a lot of energy.
If you prefer English units multiply kJ/(km-kg) by 0.173 to convert to Calories/(mile-pound)