Someone recently asked the Antiplanner whether electric trolley buses or buses powered by compressed natural gas (CNG) were a good alternative to light rail. My initial response was, “why do we need any alternative other than ordinary buses?” But I decided to take a look at the data in the 2012 National Transit Database to be sure that was an appropriate answer.
Five cities–Boston, Dayton, Philadelphia, Seattle, and San Francisco–still operate electric trolley buses. Ten major transit agencies fuel their buses exclusively or almost exclusively with CNG. Only one major transit agency uses liquid natural gas, and one uses a combination of CNG and LNG. Finally, five major transit agencies fuel their buses exclusively or almost exclusively with biodiesel.
My calculations for energy efficiency in BTUs per passenger mile and for greenhouse gas emissions in grams of CO2 per passenger mile are shown in the table below. The calculations are based on standard factors for BTUs per gallon of fuel and pounds of CO2 per million BTUs of fuel. For comparison, I’ve included the average of all motor buses, light rail, cars, and the Toyota Prius. The last column in the table shows passenger miles per vehicle revenue mile, or the average number of occupants on board the vehicle. In the table, “Electricity” refers to buses powered by overhead trolley wires.
Alternative Bus Fuels
| City | Fuel | BTUs/PM | CO2 g/pm | PM/VRM |
|---|---|---|---|---|
| Bakersfield | CNG | 8,276 | 439 | 6.3 |
| Boston | Electricity | 5,823 | 320 | 10.2 |
| CT DOT | Biodiesel | 4,844 | 127 | 8.1 |
| Dayton | Electricity | 2,952 | 87 | 8.5 |
| Denver | Biodiesel | 2,550 | 71 | 15.2 |
| El Paso | CNG | 4,906 | 260 | 11.7 |
| Ft. Worth | CNG | 7,338 | 389 | 9.2 |
| LA (DOT) | LNG | 8,151 | 433 | 7.2 |
| LA (MTA) | CNG | 3,203 | 170 | 20.5 |
| Nassau | CNG | 4,829 | 256 | 15.1 |
| New Orleans | Biodiesel | 2,780 | 73 | 14.1 |
| Orange County, CA | LNG/CNG | 4,618 | 245 | 11.9 |
| Philadelphia | Electricity | 2,251 | 178 | 15.1 |
| Portland | Biodiesel | 2,890 | 76 | 12.2 |
| Riverside | CNG | 5,017 | 266 | 10.8 |
| Sacramento | CNG | 5,814 | 309 | 8.3 |
| San Diego | CNG | 4,157 | 220 | 13 |
| San Francisco | Electricity | 1,607 | 111 | 16.2 |
| San Gabriel, CA | CNG | 3,559 | 189 | 10.0 |
| Seattle | Electricity | 8,269 | 493 | 12.7 |
| Tacoma | CNG | 4,959 | 263 | 9.5 |
| Twin Cities | Biodiesel | 3,142 | 87 | 10.9 |
| Average motor bus | Petroleum | 3,906 | 277 | 11.2 |
| Average light rail | Electricity | 3,400 | 171 | 25.4 |
| Average car | Gasoline | 3,193 | 227 | 1.7 |
| Average Prius | Gasoline | 1,600 | 118 | 1.6 |
The table shows very mixed results for trolley buses. On average, trolley buses use 3,900 BTUs per passenger mile, compared with 3,909 for ordinary transit buses (“motor buses”), so there is no real savings. If the electricity powering trolley buses comes from non-fossil fuels, they might be greenhouse gas friendly, but that will be the case only in a few parts of the country.
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Biodiesel does quite a bit better, using fewer BTUs and emitting less than a third as many grams of CO2 per passenger mile. But this depends on the grade of biodiesel that the agencies are using; if they are using fuel that is mostly regular Diesel mixed with a small amount of biodiesel, then they will be emitting a lot more greenhouse gases than shown in the table.
Really, the best way for transit agencies to reduce their environmental impact is to make better use of their existing fleets. Not surprisingly, systems that fill a higher percentage of seats use less fuel and emit less pollution per passenger mile. Buying bigger buses that run around empty all the time will do little for the environment even of those buses are powered by some alternative to ordinary Diesel fuel.
The second-best way is to substitute biodiesel for petroleum Diesel fuel. CNG, LNG, and other alternative fuels add significantly to the cost of new buses yet do relatively little to protect the environment.
Since most transit uses more energy and emits more greenhouse gases per passenger mile than the average car, the best thing individuals can do to protect the environment is to drive environmentally friendly cars such as the Prius. While riding a transit line that already exists may have little environment impact, supporting new transit improvements such as rail transit or buying alternative-fueled buses does more harm than good.
In short, my initial impression was correct: the alternative to light rail is not some fancy or expensive new bus, but simply ordinary buses. Transit agencies should focus on filling seats, not glitzy new technologies.
“CNG, LNG, and other alternative fuels add significantly to the cost of new buses yet do relatively little to protect the environment.”
Please define ‘environment’ very carefully. Particulate emissions from diesel buses are nasty, particularly where buses congregate. Diesel-electric hybrid buses massively reduce particulate emissions, but don’t cost that much more, only a few cents per seat-mile. Transport for London (TfL) knows more about bus operations than I will ever do, and they have plumped for diesel-electric hybrids, and have rejected the costs of trolleybuses.
I get motion-sickness on busses if I try to read a book or play a game on my smart phone. I don’t get motion sickness on the train if I do the same.
That is the reason I would pick a train over a bus.
If someone wants to develop new technologies for busses they should try to resolve those issues. Invent a suspension system and a driving network so the bus won’t give you motion sickness with all the starts and stops and 90 degree turns.
This is a time when I think looking at real world examples is a poor way of doing it. The high variation in efficiency has nothing to do with the choice of how to power the bus/trolley, but of how the routes are laid out and how frequent runs are. A better comparison would be to take an example system, and calculate the cost vs. savings of converting the system to CNG/LNG/diesel/etc.
The Antiplanner wrote:
The table shows very mixed results for trolley buses. On average, trolley buses use 3,900 BTUs per passenger mile, compared with 3,909 for ordinary transit buses (“motor buses”), so there is no real savings. If the electricity powering trolley buses comes from non-fossil fuels, they might be greenhouse gas friendly, but that will be the case only in a few parts of the country.
There is one compelling reason for some urban transit systems to run electric buses instead of those powered by more-conventional liquid or gas fuels – transit routes with steep grades (such as those found in municipalities like San Francisco). On bus routes with steep hills, the trolleybus is going to scale those grades easier than a conventional bus can, because the electric motors have more low-end torque, especially as the bus pulls away from a stop.
Does that make them a perfect application on all transit routes? No! Especially when the capital and maintenance costs of installing the poles and and hanging the wires to provide the traction power to the buses is included.
“If the electricity powering trolley buses comes from non-fossil fuels, they might be greenhouse gas friendly, but that will be the case only in a few parts of the country.”
As it is in Seattle, where only 0.8% of electricity comes from coal (if Seattle City Light is being honest). Makes sense here.
Vancouver BC has used the electric trolley buses for years. BC is powered almost exclusively with hydroelectric power, so here the trolley buses are low in GHG emissions. The routes they are used on in Vancouver are almost all very busy routes with high ridership.
The electric trolley buses are nice for being quiet, they are not nice when it comes to moving anyone anywhere quickly. They can not pass each other along routes meaning they have a tendency to clump together. If there is an obstacle on the route the electric trolley buses need a lot longer time to get around them because the driver has to get out and unhook the bus from the wires, drive around the obstacle and then get the bus hooked up again.
Only on a very few inner city routes do they make any sense, even then are they worth it. In Vancouver one of the main routes was along Broadway but they were so slow that they dissuaded people from using transit. The 99B line was created with conventional buses and it was much faster and is now one of the most used bus routes in North America with a higher ridership than any LRT line in Portland
“If there is an obstacle on the route the electric trolley buses need a lot longer time to get around them because the driver has to get out and unhook the bus from the wires, drive around the obstacle and then get the bus hooked up again.”
Those are old trolleybuses. Modern trolleybuses have a winding drum on the roof of the bus, so that the driver can lower and raise the pickup from within the driver’s cabin.
“Transit agencies should focus on filling seats, not glitzy new technologies.”
It won’t happen. Organizations – private or public, not for profit or for profit – focus on where they get their money from. In the case of transit, the lion share and then some comes from politicians. Until the government gets out of the transit business, it will always be politics, not the riders.
Driving a Prius is much worse for the environment than getting on a bus that’s already running. As the AP points out buses often have unused capacity, so the best thing an individual can do is make use of it.
The AP is missing an opportunity here. The main appeal of lrt is their place making effect. Quiet electric trolley buses can be a decent substitute in a way that ICE buses never could. Add in some street beautification, off board POP for all door boarding, and a bus/emergency vehicle lane for reliability.
Also, if a region gets 40% of its electricity from hydro, solar or some other renewable source, will it get 40% of the marginally product electricity when the bus is run from those sources? Or were they being fully utilized and powering an extra trolley bus means burning more fracked natural gas?
The information in the table can’t answer whether one vehicle is more fuel efficient than another because the data are weighted by passenger load. Knowing that Bus #1 uses X BTUs per P-M and that Bus #2 uses Y BTUs per P-M, tells us nothing about which bus is a better alternative.
A 5-passenger SUV that gets 15 V-MPG gets 75 P-MPG with 5 passengers. A 5-passenger Prius that gets 50 V-MPG gets 50 P-MPG with just the driver. Which one is “the better alternative”?
A vehicle-for-vehicle comparison would be very useful though.