Many brochures, web sites, and other documents promoting particular rail transit projects often say, “Congestion in this region is bad and it is only going to get worse. So we need to build this rail line.” Note that, if they are honest, they don’t promise the rail line will relieve congestion–they only imply it. The most honest ones will say that the rail line will give people an alternative to congestion. None will admit that many rail lines will actually make congestion worse.
Very few rail transit lines built in the last fifty years carry enough people to relieve congestion. The San Francisco BART line relieves congestion on the Oakland Bay Bridge, but probably not elsewhere in the region. The Washington Metro line may relieve congestion on lines crossing the Potomac from Virginia as road crossings and the highways leading to them can be bottlenecks, but probably not on the Maryland side of DC.
Most other lines probably have made congestion worse. Streetcars and most light-rail lines that operate in streets take fewer cars off the road than the reductions in street capacity that results from dedicating or sharing lanes with rail cars. For example, a traffic analysis for a proposed Anaheim streetcar predicted that it would take less than 300 cars per hour off the streets, but would reduce the streets’ capacity to carry cars by 1,100 cars per hour.
Rail lines can increase congestion even where they parallel, but do not cross, major highways. When Minneapolis’ Hiawatha light-rail line opened in 2004, the rail line crossed many minor streets that were perpendicular to Hiawatha Avenue. Since the traffic signals on the minor streets were coordinated with the signals on Hiawatha, operating the light rail disrupted traffic on both the cross streets and Hiawatha Avenue itself, adding 20 minutes to many peoples’ journeys.
Commuter rail can also make congestion worse when it frequently crosses streets. The environmental assessment for the proposed North Corridor commuter-rail line in Charlotte calculated that, without the commuter-rail line, average morning rush-hour speeds in the corridor would be 21.3 miles per hour in 2030, while adding the line would reduce those speeds to 17.9 miles per hour.
Even heavy-rail lines that never intersect streets can add to congestion near rail stations. The environmental impact report for the BART line to San Jose said that the new line would take an average of just 59 cars per hour off of parallel freeways that carry nearly 10,000 vehicles per hour. But if the line were built, there would be “significant unavoidable vehicular traffic impacts would occur at 19 intersections” near proposed BART stations.
Similarly, the environmental impact statement for the Honolulu rail line predicted that the line, which is entirely elevated above streets and highways, would nevertheless significantly increase congestion at six to nine intersections near rail stations. Meanwhile, the line would not carry enough riders to significantly reduce congestion on any major highway.
The writers of environmental impact statements often present data to deceptively claim that rail transit will reduce congestion. For example, the final environmental impact statement for Maryland’s Purple Line compared congestion in the future if absolutely nothing were done to relieve congestion with congestion in the future if the light-rail line were build and other measures were taken to mitigate congestion such as coordinating traffic signals and adding right- and left-turn lanes to congested intersections. The analysis concluded that congestion would decline at a majority of intersections, but those declines were probably more due to the mitigation measures than the light-rail line.
The traffic impact analysis for the Purple Line’s draft environmental impact statement was more honest, predicting that average travel speeds in the future would be 24.5 mph if the line were not built but only 24.4 mph if it were built. One-tenth of a mile per hour doesn’t sound like much, but when multiplied by all of the miles that planners expect will be driven in the region in the future, it adds up to 36,000 hours of more time wasted per day if the light-rail line is built than if it is not.