The Public Purpose
Number 23 September 1998

New Urban Rail in America:
Miniscule Impact on Traffic Congestion

Engineering News Record Invited Rail Commentary by Wendell Cox

A number of US urban areas have built, are building or plan to build new urban rail (light rail or metro) systems. Public support for these projects is largely based upon the expectation that the new rail systems will materially alleviate traffic congestion. This is not the case.

Traffic volumes are growing in all US metropolitan areas. An often used measure of traffic congestion is the Federal Highway Administration/Texas Transportation Institute Roadway Congestion Index (RCI). Since 1982, traffic congestion has grown from 18 percent to 55 percent in the metropolitan areas that have built or expanded rail systems (Table #1).(1) Traffic congestion has risen more rapidly in new rail metropolitan areas than in areas that did not open rail systems (Figure #1).(2)

The transit ridership increases (including those attributable to rail), that have occurred in the new rail cities have had no material impact on traffic congestion. It is estimated that the Roadway Congestion Index has been reduced in only one(3) of the new rail urban areas, Washington, and there by only 1.5 percent, from 1.43 to 1.45 if the new transit riders had instead traveled by automobile (Figure #2 and Table #2).(4)

In no case has new rail service been shown to have a noticeable impact on highway congestion or air quality.(5)

This is reflective of one of transit's fundamental problems --- that its market share is so small that significant ridership increases do virtually nothing to reduce traffic congestion.(6)

Table #1

Change in Traffic Congestion Index: New Rail Cities

Urban Area 1982 1994 Change
Atlanta 0.91 1.18 29.7%
Baltimore 0.84 1.06 26.2%
Los Angeles 1.22 1.52 24.6%
Miami 1.05 1.32 25.7%
Portland 0.87 1.11 27.6%
St. Louis 0.83 0.98 18.1%
Sacramento 0.80 1.06 32.5%
San Diego 0.78 1.21 55.1%
San Jose 0.86 1.06 23.3%
Washington 1.12 1.43 27.7%
New Rail Urban Areas 29.0%
Other Urban Areas (Over 1 million) 22.2%
Overall 23.8%

Table #2

Impact of Rail on Traffic Congestion Index (RCI)

Urban Area Base Year RCI 1994 If No Rail Impact
Atlanta 1979 1.18 1.18 0.41%
Baltimore 1983 1.06 1.06 0.00%
Buffalo 1985 0.77 0.77 0.00%
Denver 1993 1.07 1.07 0.01%
Los Angeles 1990 1.52 1.52 0.00%
Miami 1983 1.32 1.32 0.25%
Portland 1986 1.11 1.11 0.35%
St. Louis 1992 0.98 0.98 0.07%
Sacramento 1986 1.06 1.06 0.03%
San Diego 1981 1.21 1.21 0.18%
San Jose 1982 1.06 1.06 0.19%
Washington 1976 1.43 1.45 1.49%
Average 1.15 1.15 0.22%


1. Texas Transportation Institute, Texas A&M University.

2. Calculated from Texas Transportation Institute data.

3. Denver's system operated for only part of 1994. If the 1995 ridership is used instead (with a full year of rail operation), the impact on the Roadway Congestion Index would be approximately 0.1 percent. This would not change the Roadway Congestion Index.

4. Assumes new transit ridership would have otherwise have been in automobiles at average occupancy and that 12.9 percent of ridership was induced (new), based upon industry research. This new traffic (vehicle miles traveled) was added to the existing level of arterial and freeway traffic and the TTI Roadway Congestion Index recalculated assuming the higher traffic levels. Where transit ridership declined, the Roadway Congestion Index was not changed. Buffalo Roadway Congestion Index is author's estimate. If the 1981 San Diego data is used (pre-rail) the transit impact on the Roadway Congestion Index would be 0.2 percent instead of 0.1 percent --- insufficient to change the 1994 San Diego Roadway Congestion Index.

5. Jonathan E. D. Richmond, New Rail Transit Investments --- A Review (Cambridge, MA: John F. Kennedy School of Government, Harvard University), 1998, p. 95.

6. This finding is considerably different than that of a 1997 transit industry sponsored study, which concluded that transit ridership was so significant that major expansions of freeway systems would be necessary without it (Donald H. Camph, "Dollars and Sense: The Economic Case for Public Transportation in America," Campaign for Efficient Passenger Transportation, 1997)

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