ABUS RIDE DOWN Columbia Pike in Arlington takes passengers past a shiny high-rise apartment complex one minute and a combined laundromat/used-car lot the next. Tiny ethnic restaurants and bakeries abut a brand-new supermarket with huge glass windows. The road and its surrounding neighborhood are a patchwork of the upscale, down-market and diverse. Now, Arlington and Fairfax counties aim to revitalize the area by introducing a new mode of transportation: the streetcar.

Like both county boards, we think that streetcars could prove valuable. The question is whether they are immediately affordable.

The streetcar initiative has been in the works about 10 years. Arlington and Fairfax are in the final stages of planning a 4.7-mile streetcar line that would extend from Pentagon City to the Skyline area of Fairfax. Passengers would wait at a station stop, check a real-time schedule and hop on one of 10 to 14 streetcars running on inlaid rails with other traffic in the rightmost lanes of Columbia Pike.

County officials say that streetcars could ease traffic congestion. For one thing, they carry more passengers than buses. And surveys show that people are more likely to give up commuting by car for fixed-rail systems than for buses. If people do choose rail, that means better air quality, since streetcars run on electricity. A cleaner and quieter atmosphere would make Columbia Pike more walkable, more pleasant and possibly more attractive to new businesses.

The trouble is the cost. Arlington and Fairfax hope to finance the project through a combination of local dollars and federal funds from the New Starts/Small Starts program. They’re confident that streetcars will more than pay for themselves over time by spurring new investment in commercial property along the pike.

Nonetheless, the streetcar system shouldn’t be at the top of the counties’ wish lists, especially given their tight budgets. Buses are doing the job of carrying commuters down the pike, and the system could be expanded if demand increases. Because streetcars won’t have exclusive lanes, they might not reduce traffic congestion as much as the counties hope.

The streetcar project’s price tag would exceed $140 million. Because the debt-ridden federal government has made cuts to the New Starts/Small Starts program, the bulk of the cost can be expected to fall on Arlington and Fairfax taxpayers. And the counties’ money might be better spent elsewhere. For example, by 2016, most of Arlington’s public schools will be overenrolled. Perhaps funds should be used to build schools rather than a line of streetcars.

The streetcar initiative looks to the future. It could be the first step toward a revitalized Columbia Pike. But it is one of those good ideas that may need to wait.