Comments on: The Electric Car vs. Mass Transit

By: Lars Yencken

Lars Yencken — Tue, 11 Jan 2011 23:03:03 +0000

Lifecycle and infrastructure costs are important too, when accounting for energy usage. A large cost of cars at the moment is the redundancy involved in private ownership: most cars are idle most of the time. If this was factored in, I expect cars would sit far worse than they currently do in energy usage measures.

If/when cars become self-driving, schemes for collective ownership will become far more feasible. Less cars produced combined with more efficient cars may tip the energy usage scale back in their favour. Still, that’s just speculating.

By: FJ

FJ — Wed, 15 Dec 2010 04:13:40 +0000

I figured the following graph might be useful to the discussion (it plots modes of transport with respect to average speed and energy consumption):

http://www.inference.phy.cam.ac.uk/withouthotair/c20/page_128.shtml

It is taking from a great book comparing energy usages of different things in sensible numbers.

I think one should be careful about numbers for transit (buses and trains) because their energy consumption depends heavily on the people using it: There are few modes of transport more inefficient than a bus which runs empty half the trip and with 1 passenger for the other half. On the other hand, you can’t do much better than full trains.

By: Jeff

Jeff — Tue, 14 Dec 2010 17:33:15 +0000

I think we need a better metric for transportation energy efficiency than just “passenger miles traveled”. We need something along the lines of “population and service traversal,” if you will. For example, if I am in a car-oriented area and traverse one mile, I have likely not passed that many people’s homes, that many businesses, etc. However, if I take the Subway for one mile in Manhattan, I have likely passed through the equivalent, with respect to homes, businesses, cultural attractions, services, etc., as passing through ten miles in a less dense area. Sure, the “energy per mile traversed” may come out similar between the car and the Subway, but the “population density traversed”, or whatever you want to call it, is going to be much, much greater.

By: Decatur Metro

Decatur Metro — Tue, 14 Dec 2010 16:55:22 +0000

So how do I do this? I found this info on the Nissan Leaf... The energy content of 1 gallon of gasoline is 33.7 kilowatt-hours. The Nissan Leaf uses 34 kilowatt hours per 100 miles per this sticker. So assuming that the average fuel power vehicle gets 25 miles per gallon, it would use 4 gallons of gas - or 134.8 kilowatt hours to drive 100 miles. Again the Leaf would use 34 kilowatt hours. So, if a Leaf uses a quarter of the kilowatt hours to go 100 miles, I assume I can just apply that to the "car" BTU number above? So 3,437 divided by 4 is 859.

By: treesrock

treesrock — Tue, 14 Dec 2010 13:28:07 +0000

PS. I would also argue you have to consider the sources of the power source. As oil, coal comes at a very high price to the environment both in emissions and extraction of it (mountain top removal, water pollution, etc.). I guess the question is if it more palatable than oil?