Urban transit turns out to be an energy hog

Boosters regularly tout a laundry list of transit benefits; one might not stand up to scrutiny

With the exception of only a few large urban areas, transit is generally less energy efficient than personal vehicles.

Transit is often touted as a way to save energy. But since 2009 transit has used more energy, per passenger mile, than the average car. Since 2016, transit has used more than the average of cars and light trucks together.

Automobiles and planes are becoming more energy efficient each year. But the annual reports of the National Transit Database reveals that urban transit is moving in the opposite direction, requiring more energy to move a person one mile in each of the last four years.

Transit has been less energy efficient than the average car since 2009. Light trucks (vans, pickups, SUVs) may soon become more efficient than transit as well. 2018 automobile data are not yet available; 2017 numbers are estimated from this report; prior years are from the Transportation Energy Databook.

The reason for this is simple: ridership is declining, but transit agencies aren’t proportionately reducing miles of transit service. As a result, the average occupancies of buses and other transit vehicles has declined in every year since 2013. While transit agencies may be purchasing more fuel-efficient vehicles, the increase in average efficiencies per vehicle mile can’t make up for the loss in passengers.

Transit occupancies have steadily declined since 2013. Bus” includes commuter bus, rapid bus, trolley bus, and conventional bus (which the FTA calls “motor bus”). “Rail” includes commuter, heavy, light, and hybrid rail and streetcars, but not monorail or automated guideways. “All” includes all transit, not just bus and rail.

These numbers are based on the National Transit Database, which reports the number of gallons of Diesel fuel, gasoline, natural gas, and other fuels as well as the number of kilowatt-hours of electricity that are used by transit systems across the country. I’ve converted these numbers to British thermal units (BTUs) using standard factors, such as that a gallon of Diesel fuel has 138,500 BTUs.

For electricity, I also took into account the fact that two-thirds of the energy used in a power plant is lost in generation and transmission. In other words, in order to deliver 1 kilowatt-hour (3,412 BTUs) of energy to a customer, an electrical system must consume the equivalent of 10,236 BTUs of fossil fuels or other energy at the power plant. Electric motors tend to be more efficient than internal combustion engines, but when the losses from generation and transmission are accounted for, the efficiencies are about the same.

Energy Consumption by Mode

The calculations show that ferries and streetcars use huge amounts of energy per passenger mile, as do automated guideways (i.e., people movers), which aren’t shown in the chart but average even more energy per passenger mile than ferries. Buses and light rail are well above the average automobile.

Ironically, the most energy-efficient transit mode–van pools–is the one that is based on conventional automobiles rather than large buses or railcars.

Commuter and subway/elevated trains (heavy rail) appear to be more efficient, but this is largely because commuter- and heavy-rail numbers are dominated by New York where occupancy rates are high. Commuter rail lines in such regions as Dallas-Ft. Worth, Miami, and even Philadelpha use far more than the average amount of energy per passenger mile, as do heavy rail lines in Baltimore, Boston, Los Angeles, and Miami. Perhaps the biggest surprise is the DC Metrorail, the nation’s second-most heavily used rail system, which consumes almost 25 percent more energy per passenger mile than the average light truck used in 2017.

Rail BTU Use and CO2 Production

Rail SystemBTUsGrams CO2
COMMUTER RAIL
Alamont1,04476
Albuquerque3,834281
Boston2,736200
Chicago Metra1,977158
Chicago N. Indiana2,852190
Connecticut9,741713
Dallas-Fort Worth4,876357
Denver2,776178
Los Angeles2,600190
Maryland2,952181
Miami4,012294
Minneapolis North Star3,318243
Nashville6,452472
New Jersey Transit2,728108
New York Long Island RR1,85751
New York Metro-North2,75278
Orlando6,212455
Philadelphia DOT2,44087
Philadelphia SEPTA4,879175
Portland-Boston2,622192
Salt Lake City2,758202
San Diego3,118228
San Francisco1,430105
Santa Rosa SMART2,335171
Seattle1,638120
Virginia Ry Exp1,788131
HEAVY RAIL
Atlanta2,11188
Baltimore14,579552
Boston3,417127
Chicago3,391126
Cleveland4,674302
Los Angeles4,34090
Miami5,138223
New York MTA1,77034
New York PATH2,38955
Philadelphia PATH4,760110
Philadelphia SEPTA4,026144
San Francisco1,87939
San Juan2,14177
Staten Island5,344103
Washington4,342232
Light Rail
Baltimore6,933263
Boston3,421127
Buffalo7,601146
Charlotte4,091150
Cleveland15,223982
Dallas5,584286
Denver3,796243
Houston4,388224
Los Angeles3,33769
Minneapolis-St. Paul4,227197
NJ Hudson-Bergen4,682108
NJ Newark5,643130
Norfolk7,592253
Phoenix2,07683
Pittsburgh10,831388
Portland2,74334
Sacramento5,153107
Salt Lake City4,699336
San Diego2,28347
San Francisco4,31190
San Jose5,200108
Seattle1,60715
St. Louis4,182327
STREETCARS
Atlanta19,672816
Charlotte8,706319
Cincinnati13,674882
Dallas-DART26,3831,350
Dallas-McKinney4,051207
Detroit14,542730
Kansas City3,269256
Kenosha32,9382,094
Little Rock40,9612,167
Memphis18,009787
New Orleans3,337165
Philadelphia4,857174
Portland2,71533
San Francisco5,761120
Seattle13,641125
Tacoma5,14047
Tampa8,759381
Tucson12,907515
Washington56,9973,041
HYBRID RAIL
Austin2,773203
Denton5,264385
NJ River Line2,530185
Oakland3,194231
Portland3,812275
San Diego2,689197

Energy Consumption by Urban Area

The numbers for individual urban areas are even worse for transit. Among the largest 100 urban areas, transit is more energy-efficient than cars only in New York, San Francisco-Oakland, and Honolulu. Transit in Atlanta and Portland is less energy-efficient than cars but more than the average light truck. Just about everywhere else, transit is a real energy hog. The adjacent table has numbers for the 54 urban areas. Among smaller urban areas, Stock- ton (which is the 102nd largest area) appears to be more energy efficient than cars, but only because the Altamont Commuter Express is attributed to Stockton.

Even where rail transit appears to be more energy efficient than driving on an operational basis, this doesn’t account for the energy costs of construction. Urban roads carry far more passengers over their lifetimes than rail lines, so the energy cost of construction per passenger mile is much higher for rail transit. Rails must be rebuilt about every 30 years, which also requires large amounts of energy. Heavy use of steel and concrete also has a high greenhouse gas cost.

Urban AreaBTUsGrams CO2
New York2,34194
Los Angeles4,218287
Chicago3,395197
Miami4,854324
Philadelphia4,435210
Dallas-Ft. Worth6,482441
Houston4,066290
Washington4,459277
Atlanta3,172204
Boston3,477202
Detroit4,601326
Phoenix5,296389
San Francisco-Oakland2,616115
Seattle4,101280
San Diego3,648240
Twin Cities4,479300
Tampa-St. Petersburg5,601417
Denver4,027279
Baltimore4,425269
St. Louis5,062378
San Juan4,483314
Riverside7,231581
Las Vegas4,274341
Portland3,270159
Cleveland5,821417
San Antonio6,013466
Pittsburgh5,242341
Sacramento6,642392
San Jose4,531264
Cincinnati5,399394
Kansas City6,895523
Orlando5,000370
Indianapolis6,844500
VA Beach6,032419
Milwaukee5,329389
Columbus7,309565
Austin5,103373
Charlotte4,687305
Providence4,746347
Jacksonville6,514488
Memphis6,811495
Salt Lake4,011293
Louisville5,101372
Nashville5,472396
Richmond4,397344
Buffalo4,875309
Hartford4,958363
Bridgeport5,671413
New Orleans6,598458
Raleigh6,156443
Oklahoma City5,971449
Tucson5,293383
El Paso4,714390
Honolulu2,746200

Greenhouse Gases

Though transit is less energy efficient than cars, it emits slightly fewer greenhouse gases per passenger mile than the average car. Transit was actually worse than the average car as recently as 2010, but by 2014 it had reduced its climate footprint by 25 percent.

It accomplished this partly by converting from Diesel to other fuel sources, originally biodiesel but more recently compressed natural gas. In addition, the nation’s electric industry has converted from heavy reliance on coal to heavy reliance on natural gas. Both of these changes reduced greenhouse gas outputs per unit of energy. Since 2014, however, declining transit ridership increased greenhouse gas emissions per passenger mile by about 7 percent.

The main transit energy trend over the last decade has been the replacement of Diesel fuels with compressed natural gas, which paralleled the electric industry’s conversion from coal to natural gas.

Calculations of greenhouse gas emissions are straightforward for most fuels since burning a gallon of gasoline, Diesel, or natural gas results in specific outputs of carbon dioxide. For electricity, I presumed that the electricity used by a transit agency is generated by a the combination of power sources used in the agency’s state, as reported in the Department of Energy’s State Electricity Profiles. Even if a transit company claims that it buys renewable energy, the reality is that electricity is fungible, and renewable energy consumed by a transit agency means less renewable energy for someone else.

While transit scores better than automobiles overall, this is only because of New York, which produces some 44 percent of transit riders and whose electricity profile claims to emit less than half the national average of carbon dioxide per kilowatt-hour. However, New York doesn’t generate enough electricity to satisfy its needs and must import some, and the greenhouse gases attributable to imported electricity is unknown.

Two-thirds of all states are net electricity exporters, and some major exporters such as Texas and Wyoming generate most of their electricity with fossil fuels. Many of the importer states, including California and New York, generate most of their electricity from non-fossil-fuel sources, but their imports are probably more dependent on fossil fuels.

For a sensitivity analysis, I assumed that electricity brought into net importer states was generated by the national average of fuel sources. Under this assumption, electric-powered transit generated 22 percent more greenhouse gases in California, 15 percent more in New York, and about 7 percent more in Massachusetts, Maryland, and Virginia, while Washington DC transit generated 17 percent less greenhouse gases. For the most part, these numbers aren’t big enough to fuss about, especially since we can’t accurately estimate the mix of sources of energy that is imported into the various states. The greenhouse gas emissions shown in the adjacent tables are based on state electricity profiles with the caveat that the actual numbers in California and New York are probably higher while DC is probably lower.

Based on the state profiles, transit is more greenhouse-gas-efficient than cars nationwide, but it is more efficient than cars in only seven out of the nation’s 100 largest urban areas. Further, transit is more greenhouse-gas-efficient than light trucks in only three more urban areas. Thus, driving a car or light truck is more greenhouse-gas-friendly than transit in 90 of the nation’s 100 largest urban areas (and all but a handful of the smaller ones).

The results of my calculations of energy consumption and greenhouse gas emissions for each transit agency, mode, and urban area are in my 2018 Transit Database summary spreadsheet. For details on how to use this spreadsheet, see this policy brief.

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