How transit reduces road congestion

Here is an important question for metropolitan areas in Minnesota:  Does public transit reduce traffic congestion? Often the answer is "yes," but sometimes it is "no."

On the "yes" side, the link between public transportation and easing our collective commuting headache is a notably simple one: Buses and light rail trains can carry more people per vehicle and per foot of roadway than do private automobiles, meaning that as more people travel by transit instead of by car, there should be fewer total vehicles taking up less square footage and clogging up our roads.

However, the actual impacts of transit on gridlock in Minnesota are a bit more complicated for several reasons. 

First, transit can only reduce congestion on a roadway that is already being used by as many vehicles as it can hold. Transit service along an uncongested corridor or during off-peak hours won't make anybody's trip much faster.

Second, a particular bus route or rail line is likely to have a much greater impact on people's commute times when running on or parallel to a major roadway. Twin Cities examples include I-94, I-35W, Lake Street and University Avenue. Traffic congestion on a major roadway is likely to overflow onto other roadways that connect to it, so if a transit route eases gridlock on a major thoroughfare, the benefits will be felt on adjacent and intersecting streets, as well.

Third, public transportation's positive impacts on traffic flow are wholly dependent upon riders-by-choice - that is, people who could get around in private automobiles if they wanted to but hop on buses or trains instead. All other non-drivers are presumed to walk, bicycle, carpool, or use transit because they don't have any other option.  Consequently, only a rider-by-choice on transit represents another car, van, truck, or motorcycle removed from traffic.

To reduce traffic congestion, Minnesota's transit agencies need to fill their buses and trains with as many riders-by-choice as possible.

Most of the time and in most places, traveling by car is faster than transit. Therefore, in most cases, travelers must be convinced to become transit-riders-by-choice for reasons other than speed. These riders-by-choice might be drawn to transit to save money on parking and gasoline, or to relax in comfort on transit vehicles during the rush hour chaos, or to take advantage of convenient transit schedules and transit stop locations.

Unfortunately, riders-by-choice are much fewer in number now then they were a few decades ago, thanks to an automobile culture that encourages urban sprawl. But a transit system often needs to attract only a relatively small number of riders-by-choice in order to have a major impact on traffic congestion because the difference between a congested roadway and an uncongested roadway is often just a very small number of vehicles.

Mitigating traffic congestion is not the only reason for public transit, of course. Personal mobility, improved livability and reduced environmental impacts are other standout benefits. But transit definitely holds promise for easing those morning and evening commutes.

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