Trends in Mobility and Reliability:
Transportation Issues for the 21st Century
Testimony of Tim Lomax
Texas Transportation Institute*
MOBILITY, CONGESTION AND INTERMODALISM HEARING
COMMITTEE ON ENVIRONMENT AND PUBLIC WORKS
United States Senate
Dirksen Senate Office Building
*The views in this testimony are those of Tim Lomax and do not necessarily represent those of the Texas Transportation Institute, or
The Texas A&M University System
Mr. Chairman, distinguished members of the Committee, thank you for the opportunity to testify before you today. I have been asked to summarize a few trends that we have identified in a report we prepare each year on urban traffic congestion. I will also offer a few observations about congestion in U.S. cities in the next few years. I would like to build on the excellent information that Mr. Pisarski has prepared. Please keep in mind his summary of how travel demand has grown and how it will continue to grow in the future.
Over the last 20 years our cities have not been able to keep pace with the demand increases brought on by population and job growth. Congestion has increased as a result of that imbalance. Our data shows that during peak travel periods in 76 urban areas we studied, the travel time penalty – the extra time it takes to travel during the “rush hours” – has increased 185% since 1982. The penalty in areas with populations between 500,000 and 3 million increased by 300% over this same time. This indicates that while most of the problem is in the large metropolitan areas, the congestion problem is growing in areas of all sizes. Total hours that travelers in these 76 areas were delayed increased from 750 million in 1982 to 3.6 billion in 2000.
This congestion growth was the result of the trends that Alan referenced. In just our 76 areas, travel demand increased 86%, but road capacity only increased 37%. The real capacity increases were much less; the 37% value includes many roads that were incorporated as a result of growing urban area boundaries, rather than newly constructed roads. The imbalance is the result of several truths and myths about what can be accomplished. I would like to emphasize just a few important elements.
First, a truth. Road construction can help reduce the growth of traffic congestion. Figure 1 shows the dramatic difference in travel time penalty growth between areas that added roads at a rate close to the rate of travel growth—the green line at the top—and those areas that added few roads in relation to their travel growth—the dark blue line at the bottom. The cities in the bottom group added roads at a rate close to travel growth—for example, a 4% annual growth in the traffic might be accompanied by a 3.5% growth in major roads. The time penalty only increased 57% in the areas that were able to add roads. Time penalties increased 245% for the “least aggressive” roadway adding areas.
Second, a myth. We should invest all our money and effort in adding roadways. My characterization of this as a myth is not based on ideology. It is based on the fact that since 1982, urban areas have added only about half of the roads needed to stop the growth in travel delay. Figure 2 shows that this percentage is about the same for all four urban population ranges we track in our annual report. This is due to a combination of factors ranging from lack of funding, land, public support, and environmentally supportable alternatives. Roads can definitely help, but realistically they aren’t the “wonder drug” prescription because cities have not been able or willing to add them quickly enough.
A similar truth can be stated about transit improvements—they can help, but cannot solve the problem themselves. Figure 3 illustrates the amount of new transit riders and carpoolers that would have to be added each year to keep pace with travel demand growth. We are looking at adding the equivalent ridership of a current transit system between every year and every four years. This is very unlikely.
Let me point out a somewhat discouraging note that “regular” traffic congestion is only part of the problem. The variations in travel time caused by crashes, vehicle breakdowns, special events, construction, maintenance, weather and a variety of other factors are a source of frustration and economic loss to person travel and freight movements. Part of our problem is that we don’t have the long-term, system-wide, detailed data we need to fully describe the issues. The emphasis on operational improvements over the last several years allows us to analyze a few years in a few cities, but these improvements need to cover more of the nation’s transportation system.
Figure 4 shows the kind of information that can be developed and how we can use it to identify problem areas and the success of improvements. This graph is for some of the Minneapolis-St. Paul freeway system in 2000. Congestion is measured by the Travel Time Index—the peak period travel time penalty shown in the dark blue line. Unreliable travel conditions are measured by the Buffer Index—a measure of the amount of extra time travelers need to allow because of the unpredictability in system conditions. We can see the effect of the big snowstorms in January and December—more congestion and very unreliable travel times. The summer tourist season is also the cause for greater variation in travel time, although not a substantial increase in average travel time penalty. We can also see the effect of turning off the traffic signals that controlled access to the freeway system. This experiment began in October, and the freeway effects were immediate and dramatic. The unfortunate part of this story is that the monitoring and data collection system does not extend to the entire system of freeways and streets so we cannot completely analyze the experiment from this data. But the limited data we have suggests that operational improvements can play a significant role in providing a more reliable transportation system for people and freight.
It appears that unless something changes we will continue to see a growth in congested travel and congested transportation systems. Projected population increases mean more travel; our cities have not been able to stop congestion growth over the last two decades and travel and population growth will continue to stress our transportation systems. If we are fortunate to have enough funds, select projects wisely, and implement them using techniques that do not result in significant delay from construction and maintenance activities, we may be able to slow down the growth of congestion, and make the system more reliable than it is now. But “reliably congested” is not really a high standard of achievement in my view. If our cities are going to have a different future than this, we will have to pursue all types of improvements and implement more projects, rather than fewer and manage both the demand patterns and the system more efficiently.
More information on Texas Transportation Institute’s urban mobility studies can be found at: http://mobility.tamu.edu