Mayor Vincent Gray, right, backed by assorted District officials, makes remarks as he welcomes the second in a fleet of three electric trolley cars for H Street earlier this month. (Bill O'Leary/The Washington Post)

When the D.C. streetcars start carrying passengers, don’t look for them to be an immediate hit as people-movers.

At first, they will operate more like a Disneyland ride than a transit system. And that’s okay, as long as this initial service lays the foundation for the system.

A letter responding to my report on plans for the H Street/Benning Road line raises some related issues about the upcoming service.

Dear Dr. Gridlock:

You quoted 156 passengers per car, which is probably correct for a crush load for design strength but no way fit for passenger service. The car should be expected to carry only 88 passengers, just three more than an articulated bus. However, they will not carry passengers for the same cost.

In 2011, the Federal Transit Administration reported that light rail, which includes streetcars, cost 70 cents per passenger mile year around, while buses’ cost in big cities was 90 cents per passenger mile.

Phoenix put in a streetcar line 20 miles long in 2008 on its busiest streets. It has been a great success. Costs are less than half the bus service costs per passenger mile, but they do not run buses over the same route. Before they restored streetcars, Phoenix was a transit-avoiding city with a low rate of bus use, but restoring streetcars has brought the riders out in droves.

But I do not see how an H Street car can make out unless it continues west on K Street to the Key Bridge. And it just cannot work well with both streetcars and Metrobus X2 on H Street.

— Ed Tennyson, Vienna

Tennyson, a consulting transportation engineer and former deputy secretary of transportation for Pennsylvania, focused on practical operating issues.

First, I agree that we’re unlikely to see 156 passengers aboard one of these cars — unless it’s the inaugural run that will be crammed with city officials and civic leaders the day service starts.

But Tennyson’s main case is about making the streetcar fit into its environment. Right now, there’s not a huge unmet need to move people between Union Station and Oklahoma Avenue.

Metrobus X2 links the McPherson Square and Gallery Place Metro stations, Union Station and the Minnesota Avenue Metro station. The H Street/Benning Road corridor is just a segment of its route. The X9 MetroExtra, a limited-stop service, links the Capitol Heights Metro station with Metro Center via the H Street/Benning Road corridor.

So why does this puny streetcar thing make any sense?

If the streetcar line were allowed to exist in isolation, it would be no more than a two-mile toy. But the Metrobus routes can be adjusted as necessary. The District, as a partner in the transit authority, has a lot to say about routing within the District.

As for the streetcars’ destinations, the District has announced a very ambitious long-term goal for a 37-mile citywide network of lines. A proposed Benning Road extension would cross the Anacostia River to connect with Metrorail. The District also has proposed an extension west from Union Station to the Georgetown waterfront.

But the streetcar project isn’t just about moving people. It’s also about neighborhood buzz and identity.

Mayor Vincent C. Gray addressed this Wednesday as he stood in front of a streetcar delivered to an Anacostia yard for testing.

Asked why people would decide to take the streetcar, he said: “Certainly in the beginning, there will be the novelty of it.” This is exactly right, and it’s important.

Gray went on to say the streetcars will help define neighborhoods. There’s “a kind of engagement” coming between the community and its new transit service, the mayor said. This will be more difficult to quantify than passenger counts, but it is significant nonetheless.

Dr. Gridlock also appears Thursday in Local Living. Comments and questions are welcome and may be used in a column, along with the writer’s name and home community. Write Dr. Gridlock at The Washington Post, 1150 15th St. NW, Washington, D.C. 20071 or e-mail