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 FeinsteinDems get it wrong: 'Originalism' is mainstream, even for liberal judges Human rights leaders warn against confirming Gorsuch Feinstein sees slipping support among California voters: poll MORE (D-Calif.) and Susan CollinsSusan CollinsGOP senators pitch alternatives after House pulls ObamaCare repeal bill Five takeaways from Labor pick’s confirmation hearing ObamaCare repeal faces last obstacle before House vote 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 McCainMcCain: Trump admin must fill State Dept. jobs McCain says he hasn't met with Trump since inauguration Overnight Defense: General warns State Department cuts would hurt military | Bergdahl lawyers appeal Trump motion | Senators demand action after nude photo scandal MORE (R-Ariz.), for instance, pledged to filibuster an extension.

(Hat tip: SenateUS)