PUBLIC TRANSIT’S EFFECT ON TRAFFIC CONGESTION

Why this report?

Most transportation planning relies on models to predict traveler behavior, traffic congestion, and future demand. Real-life transportation experiments are rare. But when they occur, they can be an important means of testing the predictions of transportation models.

One such real-life example took place in Los Angeles over a 35-day period in October and November, 2003, when the region’s transit system was shut down due to a strike. In this report, researchers analyzed traffic conditions during the strike to understand how transit actually affects congestion experienced by drivers.

What the researchers found

Researchers examined traffic data over a 28-week period that included the MTA strike.  They focused on weekday morning and afternoon rush hours, and measured traffic delay on Los Angeles freeways before, during, and after the strike.  They found that average delay increased 47% during the strike.  For freeways that ran parallel to transit lines, average delay increased even more, to between 53% and 90%.

Peak-hour delay increased dramatically during the transit strike (between the dotted lines)

Based on these observations, the researchers estimated that transit saves LA freeway commuters $2.1 billion worth of time annually that they would otherwise have spent in freeway congestion. Assuming that transit’s congestion relief benefits for arterial roads are similar to its benefits for freeways, researchers estimated a travel time savings for all commuters worth at least $4.1 billion a year.

The researchers cited previous studies showing that increasing traffic speeds raises productivity by reducing the time it takes to get from one place to another. These studies conclude that a 10% increase in commuting speed raises productivity by 2-3%. Using this estimate, researchers concluded that LA’s transit system increases productivity in the region by $1.1 – $1.6 billion per year.

Key Conclusions

Public transit investment has wide-ranging economic benefits, not only for those who ride it, but also for those who continue to drive. By giving some commuters an alternative to congestion, transit allows drivers to reach their destinations more quickly, saving time and increasing productivity. The researchers note that these benefits typically outweigh the cost of building transit by a significant margin.

Because it would not be possible or desirable to have a real-life scenario such as a transit shut-down occur in every metropolitan area, the researchers developed a model to measure transit’s impact on congestion that fairly accurately predicted the results of their study. This model can be used in other regions as well. While the exact magnitudes of the impacts will differ from place to place, the researchers found it clear that transit service can have significant economic benefits for those regions that make the investment.

Research Details

“Subways, Strikes, and Slowdowns: The Impacts of Public Transit on Traffic Congestion”
Michael L. Anderson
University of California, Berkeley and National Bureau of Economic Research
August 2013

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