D.C. OFFICIALS are soon expected to announce the start of the city’s first streetcar line in half a century. But even those who count themselves as enthusiasts of the project are finding it hard not to feel some trepidation: They worry that the planning and execution of the first trolley line has been so muddled that it will doom plans for additional lines. Smart transit is in everyone’s interest, but it’s critical that the incoming mayoral administration of Muriel Bowser (D) bring focus and rationality to the project before proceeding with any expansion. Not all mass transit is smart.

Testing is underway on the 2.2-mile line on H Street and Benning Road in Northeast and, as The Post’s Michael Laris recently chronicled, it has had a shaky beginning. Among the problems: minor streetcar-related accidents; problems in establishing rules of the road with other vehicles; and complaints from bus operators and bus commuters of being stuck behind the slower-moving trolleys. The endeavor has been dubbed “the worst transit project in America” by Vox, which noted that the city is spending lots of money on a line that not only overlaps popular and well-used Metrobus lines but also impedes travel on those lines.

No doubt some bugs will be worked out in the start up. But there are drawbacks inherent in the design of the line — notably, the placement of tracks and the failure to connect the line with other transit at Union Station — that threaten to undermine its success. “Ill-planned, ill-thought-out, ill-engineered, ill-everything” was an assessment offered by D.C. Council member Marion Barry (D-Ward 8), with which few disagree.

The District must not repeat these mistakes as it contemplates expansions. Outgoing mayor Vincent C. Gray (D) recently announced the shortlist of three potential teams to oversee the next two lines, planned for east-west between Benning Road and Georgetown and across the Anacostia. Mr. Gray had wanted to be able to proceed with contracts that would encompass all 22 miles of the first stage of the planned network, but the council cut back funding. That there has been an erosion of political will to undertake this project is not surprising, given the project’s checkered past and the questions that remain about what would be a billion-dollar-plus investment. These include whether dedicated bus lanes are a smarter and more nimble form of transportation and whether the District should take on a money-losing operation, given the investments that will be needed in the Metro system.

Mayor-elect Bowser said during the campaign that she would reevaluate the entire project. Streetcars have advantages in connecting neighborhoods and helping foster economic development, and there is no denying their charm. But it is important that there be a clear-eyed assessment of efficacy and economic viability.