A bus travels in the new bus lane on I Street NW near 15th Street NW. (Luz Lazo/The Washington Post)

Come Monday’s commute in Washington, as many as 70 buses an hour will travel in their own lane on a busy stretch of H and I streets NW.

D.C. Mayor Muriel E. Bowser (D) on Friday launched the first dedicated bus lanes the city has had in decades downtown, a project that officials say will lead to faster and more reliable bus service in the heart of Washington’s commercial district.

“We already know that dedicated bus lanes work,” Bowser said Friday standing in front of I Street NW at Franklin Square, where crews were wrapping up the red painting of the road’s right lane. “Our hope is to make buses move more quickly and attract more riders.”

The I Street bus lane starts at 13th Street NW and ends at Pennsylvania Avenue NW; the H Street lane stretches from Pennsylvania Avenue NW to 14th Street NW.

The additions will add about 1.4 miles of bus lanes downtown, the most significant segment of transit lanes in the city. The only other bus lane is on a four-block stretch, one-third of a mile of Georgia Avenue NW near Howard University.

The new lanes, part of a pilot program, will be in effect from 7 a.m. to 9:30 a.m. and 4 to 6:30 p.m. Monday through Sept. 27, and will carry more than a dozen bus routes serving the downtown core. Bicycles, charter and school buses, as well as marked taxis will be allowed to use the lanes, officials said. Other vehicles will be allowed in the lanes to make a right turn.

Their success, officials and advocates say, will be contingent upon one thing: “enforcement,” Metro General Manager Paul J. Wiedefeld said. “That is the key.”

A recent experiment with a bus lane proved that without enforcement, it’s impossible to keep the traffic out. Little enforcement on a “pop-up” bus lane on Rhode Island Avenue last year did not really discourage cars from using it, and buses encountered cars and other vehicles parked in the lane.

This time, officials say, the enforcement will be from Day 1. Tow trucks will be towing any vehicles parked on the lanes during the peak hours, and police and traffic enforcement officers will be ticketing violators. The fine for driving or parking in the bus lane is expected to be $200.

Officials said the red paint will clearly mark the bus lanes, and new signs going up over the weekend will ensure commuters know the rules.

“We plan to be fully operational on Monday, and we will be enforcing, and that includes ticketing and towing,” Bowser said.

Though it may take a period of adjustment for drivers downtown, officials say enforcement will be constant to get drivers to know and respect the rules. But some acknowledge it may be a difficult task in some parts of the route, where right-turn traffic is prevalent. Cars will be allowed to enter the lane to make right turns, which would result in regular traffic blocking the lane in some of the busiest bus hubs, such as at 15th and I streets and 17th and I streets NW.

Wiedefeld said he is confident of the city’s “strong commitment” to keep drivers out of the bus lanes and ensure a much smoother ride for bus commuters.

The new lanes are a win for riders who can get stuck in buses traveling as slow as 3 mph in downtown and for Metro and transit advocates who have long sought an expansion of a bus system that uses dedicated transit lanes to more quickly and efficiently transport people. The District is the only big city on the East Coast that lacks a network of bus lanes. Baltimore, New York, Boston and Philadelphia have them.

“Everyone knows the traffic issues we have in the District and in the region. We have to think of bus as an option to get people out of their cars, but to do that we have to provide some speed difference,” Wiedefeld said. “Buses are averaging, in some stretches 3 mph, the same speed as walking. So you got to get that at a higher level. That is what this does.”

Bowser and other city officials say more lanes are coming. A decade-old plan for dedicated bus lanes along 16th Street NW is on track for implementation next year. And, the city is allocating $122 million to redesign K Street NW to add about two miles of bus lanes by 2025.

Support for more transit lanes on area roads appears to be on the rise. A recent Washington Post-Schar School poll found majority support for transforming a general travel lane on busy streets into a dedicated bus lane during the rush-hour commutes. Fifty-six percent of D.C.-area residents say they support bus-only lanes, vs. 39 percent who oppose such a switch.

Support for bus-only lanes during rush hour is highest in the District at 66 percent, but more than half of residents in the Maryland (55 percent) and Virginia (54 percent) suburbs also support the idea. Opinion is more evenly split among those who commute by car: Fifty percent support it, and 46 percent oppose it. Among those who commute using public transportation, however, 71 percent support the idea.

Although the lanes launch as a summer pilot program, District officials say they anticipate they could become permanent.