Two senators wrote Transportion Secretary Ray LaHood asking for an evaluation of the the "cash for clunkers" program before the Senate takes up a vote to extend the program's funding this week.

Sens. Dianne FeinsteinDianne FeinsteinGraham gets frustrated in public ‘unmasking’ debate Dem senators urged Obama to take action on Russia before election Senate panel questions Lynch on alleged FBI interference MORE (D-Calif.) and Susan CollinsSusan CollinsOvernight Finance: GOP divided over welfare cuts in budget | Lawmaker loses M on pharma stock he pitched | Yellen says another financial crisis unlikely in our lifetimes Overnight Tech: EU hits Google with record fine | Amazon gears up for lobbying battle | Facebook hits 2 billion users | New ransomware spreads across globe Overnight Regulation: EPA moves to repeal Obama water rule | Labor chief to review overtime rule | Record fine for Google MORE (R-Maine), two principal authors of the initial bill, asked LaHood for key statistics on the number of cars purchased under the program, and the extent of the environmental impact expected to be gained by the program.

"We believe that Congress needs this information immediately in order to evaluate the program's effectiveness in attaining its two goals of stimulating automobile sales and reducing oil consumption," the senators wrote. "Without strong data on the effectiveness of the program, it will be more difficult for Congress to evaluate and improve the current program."

The extension of the program may face a bit more of an uphill climb in the Senate compared to the House, which easily passed the fast-tracked bill. Sen. John McCainJohn McCainLawmakers wary of Trump escalation in Syria Senators urge Trump to do right thing with arms sales to Taiwan Changing America: America’s growing education divide MORE (R-Ariz.), for instance, pledged to filibuster an extension.

(Hat tip: SenateUS)