Cars, Trains, Energy, and Danger
Wednesday, November 8, 2006 at 11:50AM A couple of striking experiences recently crossed paths for me. One was my attendance at the World Oil Conference of the Association for the Study of Peak Oil (See previous posts). The other event was someone dear to me coming within inches of being hit head-on by a moron who pulled out into the oncoming lane of traffic. The conference had already set me to thinking about alternative transportation. The near miss set me to thinking about the absurdity of our dominant mode of transportation, the automobile.
Most people in the U.S. spend an hour or more a day in a ton and a half steel box on wheels, hurtling down a twelve foot wide strip of pavement. They have to maintain constant attention, stretching the limits of their reaction time and intuitive judgement in order to avoid leaving their lane or running into someone else doing the same thing. Last year, six million people failed to do this, causing 43,000 deaths and 2.7 million injuries. The deaths alone are like two commercial jets crashing each week. Would you fly at all if that were happening? But you drive, and so do I.
Our road system came into being at a time when horse drawn carriages were the established technology, running at 5-10 miles per hour. The turning radii, grades, and sight lines were appropriate for those speeds. In many cases we have just paved over these original tracks. Cars started out as modified carriages, with single digit horsepower and top speeds in the teens. As the road surfaces and automotive technologies were improved, the weight and speed of vehicles went up, along with the death toll.
Given a one-second perception/reaction time, a carriage travelling at 6 mph would travel just 8.8 feet before the driver could yank on the reins. At a modern highway speed of 65 mph, a vehicle travels nearly a hundred feet in the same time. The kinetic energy per kilogram of the modern vehicle at highway speed is 100 times that of the carriage. Free-steering vehicles travelling a mile a minute on roads laid out for horses is a recipe for carnage.
There is also an energy problem.
Even with modern materials and design, cars need a certain amount of mass. One big reason is simply for survivability in collisions. The force of an impact on occupants is directly related to how fast the vehicle decelerates, which in turn is related to the relative mass of the vehicle to whatever it runs into. Of course, it takes energy to move this mass around.
Cars need to be much larger than necessary just to contain passengers and their luggage. All cars have extensive crumple zones, for that precious slowing of deceleration and to prevent intrusion into the passenger cabin. This increase in size increases the air drag of the vehicle, and therefore the energy consumption.
What if we abandoned the concept of a two-ton steel box rolling on a twelve foot wide paved lane? What if we went back to first principles and asked “How do we get a person and a few cubic feet of luggage from point A to point B with the least energy and most safety possible?”
Standard passenger rail is much more efficient than driving, but it has physical and social limitations. Tracks are designed for gross weights per car of up to 315,000 pounds, which is absurdly over engineered for passenger travel. A standard Amtrak passenger car weighs in at 1200 lb. per seat. The sheer mass of both rail bed and rail cars adds to the cost of laying track and running the system. The killer for rail, though, is convenience. We are used to having our vehicles wait around for us, rather than us standing around waiting for them. In rural areas there is also the issue of mass transit without mass population. It is difficult to run a transportation system economically with 80 passenger vehicles when you can’t find 80 people going the same place at the same time.
There is another option in between the private steel box and the massive rail coach – Personal Rapid Transit, or PRT. A number of designs have been proposed and some developed, but they all include lightweight, automated vehicles running on rails, each carrying up to four passengers. (See also PPTProject)
Putting a small passenger vehicle on rails would eliminate a lot of problems, foremost among them the possibility of colliding with other vehicles. A fleet of ultralight rail cars all running at a preset speed could neither head-on, rear-end, nor “t-bone” each other. This would eliminate the need for all that mass and crumple space. Rail vehicles make electrification simple, improving efficiency and reducing emissions without the need for onboard battery storage. Most importantly for public acceptance, travelers could walk into a PRT station, buy a ticket, and hop into a vehicle without waiting. Overhead track would be small enough to penetrate into the heart of a downtown commercial district, eliminating the need for separate local public transport. The whole system could be cheaper per mile than repaving an interstate highway. All this at an energy cost per passenger-mile that is a fraction of automobile travel or standard rail.
We are facing a dramatic increase in the price of oil sometime in the next decade. This will increase the cost of fuel, the cost per kilogram of manufacturing a vehicle, and the cost per mile of maintaining roads. PRT is a promising concept for maintaining affordable high speed passenger transportation despite high energy costs.
Reader Comments (5)
Hello,
Good points! Here's my own proposal...
www.pptproject.com
I would be interested in your feedback...
gary
The older I get, the more our current mode of transportation scares the shit out of me. It also scares me that when there ARE sidewalks, which is not nearly often enough, they are only a couple of feet away from these massive steel boxes hurtling around with small margins of control at very high speeds. I have been thinking about PPT a lot lately, except that I didn't even know there was such a thing so I was trying to solve all the problems of PPT by myself. I will definitely be checking out those links!
fyi, www.pptproject.com had a name change. It's now www.prtproject.com
thanks,
gary
nope, you pod folks are not going to beat the the efficiency of the bicycle which is all that will be left ASSUMING shortsighted human's economy collapses with oil, otherwise high speed rail to transportation hubs already set up to rent you a pod.
does not the 500 mph train have cars that spill on and off as they de/accelerate to stations. Get a stopped car in Cleveland, it speeds up and connects to trans-continental. You need to transfer to the car marked Denver, which splits off and slows down at former Denver airport - rent pod