Monday, June 25, 2007

Bus Transit Energy Efficiency: Local Data

A previous post suggested that transit buses may not be all that energy efficient, especially as average passenger loads have decreased over time. This undercuts the oft-made argument that heavy public investment in transit will help solve the energy crisis or combat global warming.

Today's article by Jon Hilkevitch entitled "Cutting Cost of Hybrids" provides some local data on that question. It reports that CTA's standard buses get 3.4 miles per gallon of diesel fuel.

The CTA's 2005 report for the National Transit Database states that the CTA bus system had 781,977,753 annual passenger miles and 66,811,532 annual vehicle miles. Simple division indicates that the CTA was averaging 11.7 passengers per bus.

3.4 miles per gallon times 11.7 passengers equals 39.78 miles per gallon per passenger. That level of fuel efficiency is met if not exceeded by existing hybrids such as the Toyota Prius and the Honda Civic hybrid. If two people travel in a vehicle that gets 20 miles to a gallon, their trip consumes less fuel on a per passenger basis than if they ride the bus.

If and when the CTA switches to hybrid technology, its mileage will increase to "more than 5 miles per gallon" according to the article. Let's be optimistic and assume that at some point in the next 15 year bus replacement cycle the CTA's bus fleet's fuel efficiency will double, so that buses will go 80 miles per gallon per passenger.

That level of fuel efficiency is likely to be matched by at least some of the hybrids and all-electric vehicles zipping through the congestion pricing cordons in the region 15 years from now. To the extent that more than one person occupies each private vehicle, the per passenger energy efficiency of private vehicles may exceed that of the bus even if their gas mileage is less than that of the bus (e.g., 2 people times 40 miles per gallon equals 80 miles per gallon per person).

This slicing and dicing of the data likely understates transit's potential contribution to energy efficiency. First, if the CTA can increase average bus passenger loads its energy efficiency will go up accordingly. As suggested in yesterday's post, the CTA might be able to increase passenger loads and reduce costs without inconveniencing customers by running fewer buses but supplying customers good bus arrival time information through a system like TriMet's Transit Tracker.

Second, bus transit helps support high-density transit-oriented development. Such development encourages people to take trips by non-motorized means, by walking or biking, which increases overall energy efficiency.

Third, the energy required to manufacture, market, store and repair private autos is likely higher on a per person basis than the energy required to procure and operate a transit bus.

In short, bus transit's energy efficiency currently and in the foreseeable future is nothing to write home about compared to the energy efficiency of private vehicles. Transit's biggest contribution may be in fostering communities that are not auto centric and consume less energy than the suburban communities where all transportation is by car.


jackonthebus said...

When asking for funding, CTA always relies on unlinked trips (boardings) instead of passenger miles. Obviously, though, it has the passenger mile figure.

If it works out that on a passenger mile basis, there are only 11 passengers per bus, it would appear that there are some fairly lightly loaded buses on some segments of the routes and during some parts of the day, as during the rush hour, buses are scheduled to have full standing loads, according to the CTA, which would be 70 on a regular bus and 93 on an articulated. Of course, passengers only note the rush hour crush.

The passenger mile figure wouldn't include deadheading (empty buses running in the non-rush direction to either the garage in the morning or to the downtown start of the route in the afternoon), which would make the bus even less efficient. It also doesn't include idling at the terminal, another problem noted on Ask Carole (see her response at in the penultimate sentence of her next post). Hence, if your methodology is correct, the fuel usage is worse than you thought.

Anonymous said...

I find it strange that people are fixated on "empty" buses and trains when it's so glaringly obvious that the overwhelming majority of the private cars on the street are empty. People driving alone account for the majority of car trips, so any given street or highway is likely to have an incredible waste of space in terms of person/vehicle space; far more than a given bus or train car. And if you factor in all of the empty cars parked on and off our streets, it becomes even more apparent that people focusing on bus and train capacity are at least half blind.

jackonthebus said...

It is not being fixated on empty buses to note that the purpose of a bus is to transport a number of passengers in an efficient manner, and meet the needs of potential riders, not to guarantee the driver or the rest of the transit bureaucracy jobs or increase the subsidy needed.

The Pace Vanpool Incentive Program sort of has the right idea by saying that if you have a group of 7 to 15, rent a van that costs maybe $30,000 and gets 20 mpg, rather than schedule a bus that requires a paid driver, and even if it is a 30 foot bus, costs $278,000 and maybe gets 5 mpg. It similarly appears that using a cutaway vehicle would save capital and fuel costs (the cost of one of those being $100,000).

I understand the point that an agency such as CTA doesn't have the capital funds for both a high capacity and low capacity fleet, but there is no social utility in running an empty bus. At least the person driving alone gets maybe 15-20 mpg in the city, unless driving a Hummer, and the bus gets 3 mpg for serving few.

Anonymous said...

"If two people travel in a vehicle that gets 20 miles to a gallon, their trip consumes less fuel on a per passenger basis than if they ride the bus."

I understand that your point here is about integrated average fuel consumption, but of course the marginal fuel consumption if those two people take the bus is almost zero; much smaller than if they drive!

Justin said...

...Fourth, the bus system is integrated with the rail system, and the rail system is even more energy efficient.

...Fifth, buses should get credit for keeping the cars from congesting worse than they already are. CTA buses carry 12 pax/vehicle, yet take up only the equivalent of 2-3 cars' worth of road space. Without buses, cars would be less efficient through congestion - regardless of auto technology (well, you do mention toll cordons :).

It's also worth mentioning that hybrid buses, although maybe twice as fuel efficient, save many more times the amount of toxic emissions such as VOCs and CO.

Just to play devil's advocate, is energy consumption per se a rationale to subsidize transit? Or is it just the consumption of energy derived from combusting fossil fuels?

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