Beneath the South Station rail terminal, Boston is building its first new transit line in 85 years. But the new Silver Line won't whisk tourists and commuters from South Station to the new South Boston waterfront district in sleek subway trains. Instead, it will put people on buses--or what Massachusetts Bay Transportation Authority General Manager Michael Mulhern calls "60-foot, low-floor trackless trolleys."

This "light rail on rubber wheels," as it is sometimes called, is part of a growing trend toward bus rapid transit, an idea that some 17 cities are currently using or planning to use. Bus rapid transit encompasses everything from such early projects as Seattle's bus tunnel with its underground stations to Pittsburgh's busways, which feature dedicated bus lanes and train-like stations. It also includes Los Angeles Metropolitan Transit Authority's rapid express buses, which run on regular surface streets but utilize special "signals prioritization" gear that allows the buses to zip through traffic lights.

One of bus rapid transit's advantages is that it is cheaper than light rail. According to a recent U.S. General Accounting Office survey, BRT costs ranged from $200,000 per mile on surface roads to $55 million per mile on dedicated busways. In contrast, the cost of light rail systems ranged from $12.4 million per mile to $118 million per mile.

But advocates of bus rapid transit say cost isn't its only advantage. It can often provide better service, too. That was part of the reasoning behind Connecticut's recent decision to build a 9-mile busway between Hartford and New Britain. "With bus rapid transit you can start the route way out in the hinterlands," notes Michael Sanders, transit administrator for the Connecticut Department of Transportation, "and then put the buses on the expressway into Hartford."

But buses have a big problem. People just don't like them very much. The buses that travel beneath Seattle's downtown in the 1.3-mile bus tunnel move at up to three times the speed of aboveground buses. Nonetheless, residents there recently passed a second initiative directing the city to create a monorail.

Transit officials acknowledge that buses have a bad image. People don't find them particularly sexy or wonderful, the way they do light rail, says Garet Walsh, who is with the Charlotte-Mecklenburg Planning Commission.

BRT backers insist it doesn't have to be that way. "There's no reason why you can't transfer all of the fine attributes of a rail system to a bus system," Mulhern says. "But you've got to be willing to make similar investment levels."

Boston is certainly living up to that claim. The 1.1-mile Silver Line connection to the South Boston seaport district, which will open in December 2003, is expected to cost $600 million. "Obviously the decision to invest in bus rapid transit was not the desire to save money," Mulhern says. "It was the mode that offered the best quality service for that corridor while providing the flexibility to follow development."

Other cities are hoping to achieve similar results, while spending considerably less.