Executive Summary

While congestion is a serious problem in many metropolitan areas, the actual burden it places on residents varies considerably from place to place, even when congestion levels are similar. In places where there are few transportation choices, most people are essentially trapped by congested conditions. In places with more choices, more people can choose whether to fight through congestion in their cars or avoid it by using less stressful ways to get to work.

This analysis shows that the presence of transit service makes a significant difference in the number of residents who are subject to driving in congested conditions. In places with more transit service, a smaller portion of the population drives to work each day, lowering overall exposure to congested conditions.

In determining the effect of congestion on everyday quality of life, we need to take into account both an area's level of congestion and the degree to which people avoid it by getting around without getting in the car. STPP has calculated a "Congestion Burden Index" as a first attempt at quantifying the combined effect of congestion and the degree to which people are exposed to it. This index combines TTI's measure of rush-hour traffic, the Travel Rate Index, with figures available for the portion of commuters who are subject to that congestion because they drive to work. A high ranking on the Congestion Burden Index indicates that congestion places a higher burden on residents, both because congestion is worse and because fewer of them are escaping it.

According to the Congestion Burden Index, Los Angeles maintains its number-one ranking as the place where congestion is the worst, and where residents have few options to avoid it. However, San Francisco, which has the second-worst rush-hour congestion as measured by TTI, also has almost 500,000 citizens who travel to work by means other than driving. It drops to 29th in the Congestion Burden Index. Washington DC is ranked 4th for rush-hour congestion, but with 23 percent of workers not driving, its Congestion Burden places it 31st.

Conversely, Detroit's congestion is ranked 15th in the Travel Rate Index, but the small portion of workers who avoid driving means its congestion burden is relatively high: Detroit ranks third in the Congestion Burden Index.

Transportation choice clearly has a big impact on how much congestion affects people's quality of life.

Building Roads: Does It Provide Relief?

Traditionally, transportation agencies have responded to congestion by trying to add more space to the road system. However, our analysis of the TTI data shows this has proven to be an ineffective strategy. TTI's data show that places that have built the most roads haven't had much success in slowing growth in congestion. Even though road building has been outpacing population growth in the metro areas studied by TTI, congestion has grown worse in most places.

In the last decade, the one-third of metro areas surveyed that added the most road space per person experienced a 6.5 percent increase in rush-hour congestion, compared to a 7.2 percent increase in the metro areas that added the least road capacity. The low road building areas had higher population growth than the high road building areas, eliminating population growth as an explanation for the differences between the two sets of areas. Travel delay is actually higher on average in the 23 metro areas that built the most roads.

In part road building is ineffective because adding capacity to highways actually generates additional travel, as people take additional car trips and new development creates even more demand.

Easing the Burden of Congestion

Many Americans have already decided on their own that one of the best ways to fight congestion is to turn to transit. Transit use nationwide has grown by 21 percent in the last five years, far outpacing the growth in driving. A variety of public opinion polls show people want more opportunities to take transit, walk, or bicycle, and are less interested in new roads and road widenings.

The findings of this analysis indicate that officials seeking to ease the burden of congestion should emphasize providing transportation choice over providing more road space.