Should transit buses be allowed to use the shoulders of more Washington area highways in order to avoid traffic back-ups?

A Transportation Planning Board task force that studied the idea said in its final report, released last month, that the conditions in specific corridors under consideration need detailed analysis to make sure that the benefits of so-called "bus-on-shoulder" operations will outweigh the costs of implementation.

Eleven metropolitan areas in the United States currently allow buses to use shoulders to bypass heavily congested travel lanes on at least some routes, the report says. The Washington region is one of those, where buses are allowed to use the shoulder on a stretch of the Dulles Airport Access Road near the West Falls Church Metrorail station, as well as on a four-mile segment of Route 29 in Montgomery County.

Federal Highway Administration.

Proponents cite the time savings buses can achieve by avoiding traffic back-ups as a key reason to allow the practice. They say that the time savings increase the on-time reliability of buses, helping to move people more efficiently and making bus transit a more practical and attractive travel option for commuters looking for alternatives to driving to and from work.

During its yearlong study, the TPB task force reviewed the experiences of other metropolitan areas and talked with area transportation officials to learn what it would take to expand bus-on-shoulder operations to more highways in the Washington region.

The task force found that allowing buses to use shoulders is not as simple and straightforward as it might seem. A number of challenges, like widening and repaving shoulders to handle more regular use by heavier transit vehicles, training bus drivers on the safe operation of bus vehicles on narrow shoulders alongside slower-moving traffic, and keeping shoulders clear of snow and debris, can all make implementation harder and more expensive.

Other complications arise when shoulders are too narrow and can't be widened, like at overpasses where bridge abutments encroach on shoulders, and where buses must weave through merging traffic at highway on- and off-ramps.

The task force looked at three specific corridors in the region where the benefits of bus-on-shoulder operations -- measured mainly in total potential time savings -- might have the greatest likelihood of outweighing the costs of implementation. The corridors were I-270 and MD-5/US-301 in Maryland, and I-66 inside the Beltway in Virginia, where the Virginia Department of Transportation has already conducted an in-depth feasibility study and is planning a pilot bus-on-shoulder program for 2014.

On certain stretches of I-270, the task force found, bus-on-shoulder operations might make sense, because travel speeds routinely drop below 35 miles per hour -- a key threshold below which other metropolitan areas allow buses to use shoulders -- and daily bus ridership tops 14,000 passengers.

As part of the task force study, the Maryland Department of Transportation estimated the cost of the necessary shoulder upgrades to be as much as $8 million per mile, which would cover widening shoulders to a width of 11 feet and paving to a depth of 7 inches, the same as normal travel lanes.

In light of the challenges identified in the report, the TPB task force's main recommendation, aside from further study, is that bus-on-shoulder implementation initially be focused in short segments where congestion is especially severe, where existing bus ridership is high enough to produce significant benefits, and where expensive shoulder improvements can be incorporated into scheduled maintenance and upgrades to existing roadways to keep costs lower.

The task force's full report is available online at www.mwcog.org/bostf and is scheduled to be presented to the Transportation Planning Board at its meeting on October 16.