Enhanced buses along the proposed Purple Line in Maryland’s D.C. suburbs would cost less, offer similar services and fight global warming better than light-rail cars, according to an analysis released today by the World Resources Institute (WRI).

“The effort to create any kind of sustainable transit solution in the D.C. area is commendable, but it should be done the right way,” said Greg Fuhs, lead author of the WRI analysis. “We aren’t opposed to light rail in general, but we just don’t think it’s the best option for this particular project.”

The Purple Line is a proposed 16-mile, east-west transit corridor running parallel to the Capital Beltway in Maryland, and is intended to ease congestion and improve area mass-transit options. The two primary modes under consideration are light rail transit (LRT), featuring electric streetcars on rails, or bus rapid transit (BRT), which features designated lanes and other enhancements to make trips faster and more comfortable for riders than conventional buses.

WRI submitted its analysis to the Maryland Transit Administration (MTA) this week. It compares BRT and LRT in the “medium investment” range, and confirms that BRT would be more cost-effective and lower-risk. In addition, WRI’s analysis confirms that BRT is the only option that would work locally to fight global warming, with a medium-investment system cutting carbon dioxide emissions by almost 9,000 metric tons per year, equivalent to taking about 1,600 cars off the road.

Unlike a conventional bus system, BRT would provide high-capacity express buses with multiple doorways and pre-paid ticketing, as well as frequent pick-ups from permanent bus stations with elevated platforms similar to a rail station.

MTA estimates that medium investment BRT would require $580 million in capital investment and $17 million in yearly operational costs. In comparison, an equivalent LRT system would cost more than double, requiring $1.2 billion in capital and an annual $25 million for operations. But WRI’s analysis found that MTA’s cost and ridership estimates are likely to be off target.

“Our analysis shows a 79 percent chance that medium investment light rail will exceed $1.5 billion. On the other hand, the probability of reaching such high costs for BRT is negligible,” said Dario Hidalgo, WRI’s senior transport engineer. “Ridership is also likely to be smaller than projected for all the options, but the impact on cost effectiveness is much smaller for BRT than LRT.”

MTA officials are expected to make a final decision on the choice between BRT and LRT in March or April, after reviewing public comments.