Return of trackless trolleys bypasses South Phila.

In Seattle, "whenever there is talk about putting buses on trolley routes, people start to reach for their guns," said Jim Boon, manager of fleet maintenance for King County Metro.

The agency has 159 trackless trolleys in a fleet that includes 1,300 buses, and Boon said the agency was "committed to trolleys. They're 100 percent green. There's no thought about replacing the trolleys."

The Massachusetts Bay Transportation Authority introduced 28 trackless trolleys in Boston four years ago, and runs 32 "dual mode" trackless trolleys that operate off-wire with diesel generators for part of their routes. The agency has 1,040 buses.

"The MBTA has been pleased with the performance" of the trolleys, spokesman Joe Pesaturo said.

With buses, SEPTA officials said, routes can be altered without the need for overhead wires, and detours are no problem.

SEPTA is building its future on electric-diesel buses designed to use 25 percent less diesel and create less pollution than the buses they will replace. SEPTA has 32 in service now and estimates the operation and maintenance cost at $2.60 per mile.

SEPTA is spending $212.4 million to buy 400 of the hybrid buses over the next four years. The hybrids cost about $160,000 more than a standard bus, an amount SEPTA hopes to largely recover in reduced fuel and maintenance costs. The first of the new hybrids is to arrive by August.