A wave of new, smaller Metro buses has rolled into service throughout the northern part of the District, navigating narrow neighborhood roads where larger buses sometimes had trouble.

"The bus is lighter and smaller, and it allows us to get deeper into the neighborhoods," said Jack Requa, Metro's chief operating officer for buses. "It's a friendlier bus."

The 40 new buses, which are squat and boxy, are 26 feet long and can carry 22 seated passengers. They are the shortest in Metro's fleet of 1,300 buses, which are up to 65 feet long. The most common Metro bus is 40 feet long and seats about 45 passengers.

The 26-foot buses are being used mostly on existing routes usually served by 30-foot buses, which carry about 30 seated passengers, and on some new neighborhood routes that connect to Metrorail stations. In some cases, the shorter buses have been plugged into routes where riders did not fill the longer buses, Requa said.

The new buses are the first Metro buses with low floors; passengers board without walking up steps. Because the floor is lower than on traditional buses, passengers sit even with surrounding cars and trucks, instead of perched above traffic. Windows are larger on the smaller buses.

"A lot of people like the idea that you walk in and onto the floor," Requa said. "That's certainly true of elderly riders and people with small children who don't want to climb those stairs."

Metro bought the 40 buses, built by Orion, at a cost of $218,000 each. They are expected to last 12 to 15 years. The District government requested and paid for the buses, saying they were needed to bring transit into older neighborhoods where streets are narrow and conditions too cramped for more traditional buses, Requa said.

Some of the shorter buses began service in July, and the rest began running Saturday. The small buses are being used on Route D2 between Glover Park and Dupont Circle and Route D4 between Ivy City and Union Station, among other routes.

Ridership figures on the new buses are not yet available, said Cheryl Johnson, a Metro spokeswoman.

"We're in a test mode now, trying to see how well the customer receives it, how the District receives it," Requa said.