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 Emiel FeinsteinSenators push mandatory sexual harassment training for members, staff Bipartisan group of lawmakers aim to reform US sugar program Senate panel to hold hearing on bump stocks MORE (D-Calif.) and Susan CollinsSusan Margaret CollinsBipartisan group of lawmakers aim to reform US sugar program A bipartisan bridge opens between the House and Senate Gaming the odds of any GOP tax bill getting signed into law 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 Sidney McCainGOP rushes to cut ties to Moore GOP strategist: 'There needs to be a repudiation' of Roy Moore by Republicans World leaders reach agreement on trade deal without United States: report MORE (R-Ariz.), for instance, pledged to filibuster an extension.

(Hat tip: SenateUS)