There’s been a few threads lately regarding trains of various types, and why the U.S. doesn’t rely on them more. The answer is that the U.S. is much more distributed than Europe, the cities are bigger and more spaced out, and communities are spread out like dots in all directions. Building a feasible passenger train network between them all in a way that was convenient and not hellishly expensive seems like an impossible task. But some people think it’s important enough that they advocate rebuilding our cities and packing people in tighter to facilitate train movement.
So this got me thinking about trains in general, and what they’re made of and what makes them so efficient. These are the beneficial engineering aspects of trains:
- they have a diesel-electric locomotive, which is very efficient.
- They roll on steel tracks using steel wheels, which keeps rolling resistance down.
- They are very long, which minimizes aerodynamic drag. The frontal section of a train is miniscule compared to its overall size.
What makes a car so inefficient?
- The engine has to be sized for decent acceleration, meaning it bigger than it needs to be for cruising at highway speeds.
- The tires are rubber for good traction, which increases rolling resistance.
- The car is small on comparison to its frontal area, making it aerodynamically inefficient.
Now, think about the new generation of cars that are coming - plug-in hybrids and pure electrics. A plug-in hybrid with a diesel generator is basically a small diesel-electric locomotive.
One of the problems with electric cars is the size of the battery needed to travel long distances. Plug-in hybrids solve this by adding a generator.
It occurs to me that if you take five or ten electric or hybrid vehicles and put them together, you’ve got a mini train.
The car train.
Here’s how it would work: You’re planning to travel to another city. You go on the internet, and put in your departure time. Other people do the same. When enough people are departing at the same time and want to participate in a train, they are all issued a code number that allows them to identify themselves. You drive to the departure area, and a device in your car identifies all the cars that want to take part in the train. You all join up, connect cables from one vehicle to the next, and depart.
Computers aboard each car maintain separation and manage power flow to each motor. Some motors shut down completely. You only use as much motor as you need. It’s like the ultimate in variable displacement technology.
Each vehicle is right up against the next (we might even use trailer-hitch type connectors to lock the cars together). Therefore, you get the aerodynamic benefits of a real train.
Only the lead driver has to ‘drive’. Every other car responds to steering inputs from the lead car and follows it. Everyone else can sleep, or do work, or whatever.
As the train moves, computers calculate the drag of each vehicle and figure out its contribution to the energy use of the entire train. At the destination, a charge is assessed to each vehicle, the train stops at the ‘train station’ (little more than a roadside turnout), the train breaks up, and everyone continues on their merry way.
If you don’t like the purely ad-hoc mechanism, you could do this:
The ‘Commercial’ car train:
The lead vehicle is actually a commercial ‘locomotive’, which looks like a minivan and basically is full of batteries. The driver is a licensed ‘train operator’. They leave on a schedule. You just drive to a station, hook up to the next departing ‘locomotive’, wait for a few more to join up, and take off. The locomotive provides battery power to all the cars, and computers decide which car’s motors should be run. You get to your destination with your battery still full, and pay the locomotive your share of the energy cost.
It seems to me that if such a thing existed, you could use market forces to really drive efficiency. For example, you could buy a car with retractable ‘train wheels’, which would have extremely low rolling resistence. Once you’re in the train, you deploy your train wheels, and save money. Or perhaps the train’s computers would look for the most efficient engines and use those. If your car is picked, you get a discount to account for the fact that you’ve improved the entire train’s efficiency. So there’s a big incentive to buy highly efficient cars.
Any thoughts on this? The obvious flaw is safety - with vehicles packed so closely together, an accident multiplies in deadliness. A poorly maintained train car could break in a way that endangers the entire train. A lousy driver at the front endangers everyone else. So we’d need to solve that issue. But that seems like a much more tractable problem that cross-crossing the country with high-speed rail lines and solving the problem of how to get where you’re going once you’re off a regular train.
The beauty of all this is that it could be done with no infrastructure changes whatsoever. You could have ‘train-able’ cars, and once which aren’t, and they can coexist. You have all the benefits of a car at your destination, and most of the benefits of a train while traveling between cities. A ten-car train wouldn’t be much longer than a double-trailer semi.
Right now, I can imagine that this would make a good science fiction story, but how practical do you think it would be? How much energy would a ‘car train’ save, and would it be worth it? I’ve never seen this idea written up before that I can think of, and I’m wondering why.