Is Public Transportation Actually That Environmentally Friendly?

One Friday afternoon I found myself sitting alone on a large city express bus. Stop after stop no one got on and for about ten miles I was the only one on the entire bus route. I started thinking am I actually saving that much energy by taking public transportation instead of driving a car? A major rationale supporters of mass transit use is that by reducing our output of greenhouse gases and other pollutants, transit can help save the environment. However, when you think about empty or underutilized transit that may not be the case. At any given time, the average auto has around 1.6 passengers, the average (40-seat) bus has only 10 and rail vehicles has on average 25. The average load factor (percentage of seats filled) is also not that high 46 percent for heavy rail systems and 24 percent for light rail. According to the Department of Energy’s Transportation Energy Data Book, in 2010 transporting each passenger one mile by car required 3447 BTUs, bus required 4118 BTUs and rail transit was a bit greener at 2520 BTUs. However when you also take into account the source of transit’s energy it is usually electricity for rail and natural gas for buses, both sources are produce fewer greenhouse gases than gasoline. Also when you take into account the environmental costs of building the vehicles and infrastructure they produce slightly fewer pounds of CO2 than autos.

Trying to increase ridership by adding transit service will not help the situation since new service promises would reduce transit’s already less-than-spectacular load factors and result in largely empty vehicles. Most high density cities like New York and San Francisco already have robust transit systems and expanding to other low density cities just doesn’t make sense. For example the heavily used New York subway system (58 percent seats typically filled) produces .171 pounds of CO2 per passenger mile, less than 1/3 the average for cars nationwide. The much more lightly used Cleveland, Pittsburgh and Memphis light rail systems actually produce considerably more CO2 per passenger mile than cars.

Despite these grim facts all hope on public transit systems should not be lost. If travelers can be persuaded to leave their cars and ride existing transit services, rather than create new services, the environment will benefit greatly. Given its current low load factors, transit generally has plenty of capacity to absorb new customers with practically zero additional energy expenditure. It makes more sense for cities to create push or pull factors to increase ridership than building infrastructure and buying vehicles. Cities can give fare discounts to pull riders to ride transit or push factors like gas taxes, congestion tolling, or charging market rates for street parking to help raise push people away from cars and/or increase auto efficiency through incentives for carpooling.

So to answer the question that arose from my lonely bus ride in Austin, yes it is good to ride the bus or metro, but only if it already exists. In cities like Austin that are low density with high sprawl doesn’t make sense to create lots of new bus/metro routes unless the city can be absolutely certain that there will be a high load of users. Instead we should all put in the effort leave our cars and take the transit that is already there for us to use (click here to find the most convenient metro route for your trip). Hopefully, more people will catch on to the public transit bandwagon and I will never find myself alone on the bus again.

(Economic Info from Freakonomics)

–Juhi Amodwala, Green Offices Program Coordinator



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