Brad Templeton looks at the per-passenger cost of taking public transportation vs. other types of transportation (such as cars and bikes) and finds that the greenness of public transportation has been much exaggerated (see chart above).
A full bus or trainload of people is more efficient than private cars, sometimes quite a bit more so. But transit systems never consist of nothing but full vehicles. They run most of their day with light loads. The above calculations came from figures citing the average city bus holding 9 passengers, and the average train (light or heavy) holds 22. If that seems low, remember that every packed train at rush hour tends to mean a near empty train returning down the track.
Transit vehicles also tend to stop and start a lot, which eats a lot of energy, even with regenerative braking. And most transit vehicles are just plain heavy, and not very aerodynamic. Indeed, you’ll see tables in the DoE reports that show that over the past 30 years, private cars have gotten 30% more efficient, while buses have gotten 60% less efficient and trains about 25% worse. The market and government regulations have driven efforts to make cars more efficient, while transit vehicles have actually worsened.
My figures suggest the city bus moves 3,000lbs of bus for every passenger on average, and still 500lbs per passenger when fully packed at rush hour — starting and stopping all the time.
In order to get people to ride transit, you must offer frequent service, all day long. They want to know they have the freedom to leave at different times. But that means emptier vehicles outside of rush hour. You’ve all seen those huge empty vehicles go by, you just haven’t thought of how inefficient they were. It would be better if off-hours transit was done by much smaller vehicles, but that implies too much capital cost — no transit agency will buy enough equipment for peak times and then buy a second set of equipment for light demand periods.
Some cities do much better than others, and some countries do much better than the US:
This Australian Study cites figures saying that Western Europeans use only 76% of U.S. BTUs/pm in their private transport, and only 38% in their transit — 2.5 times more efficient. Rich Asians do even better at transit — they are almost 4 times as efficient in terms of energy/passenger-mile.
Their private transport is better because they own a lot more motorcycles and scooters, as well as smaller cars. Asians do almost 10x as many miles in motorcyles as Americans. Their transit is better primarily because of ridership. They take 5 to 7 times as many transit trips per person. Asian transit actually attains a higher average speed than private travel, another big booster.
They also have much more efficient vehicles.
Note however that in spite of their much higher ridership, transit in Europe is still only 7% of private vehicle energy use, and I would guess about 5% of total compared to ~1% of total for the USA. Even they have the automobile bug pretty strongly.
It’s worth taking a look at:
Templeton wonders if it might be more worthwhile to push people towards more fuel efficient vehicles. Along those lines it’s worth considering the MPG Illusion.
(via Robin Hanson, who has a considerably less positive view of transit than Templeton)