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 FeinsteinOvernight Regulation: Trump repeals 'blacklisting' rule Dems delay Senate panel vote on Supreme Court nominee Dems get it wrong: 'Originalism' is mainstream, even for liberal judges MORE (D-Calif.) and Susan CollinsSusan CollinsSenate braces for fallout over Supreme Court fight Overnight Finance: WH wants to slash billions | Border wall funding likely on hold | Wells Fargo to pay 0M over unauthorized accounts | Dems debate revamping consumer board Lawmakers call for pilot program to test for energy sector vulnerabilities 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 responds to North Korean criticism to calling Kim Jong-un 'crazy fat kid' Overnight Finance: Dems seek probe of acting SEC chief | Defense hawks say they won't back short-term funding | Senate seen as start point for Trump infrastructure plan | Dems want more money for IRS Overnight Defense: Pentagon considers more troops for Afghanistan | McCain, Graham won't back short-term funding | GOP defends Trump rules of engagement MORE (R-Ariz.), for instance, pledged to filibuster an extension.

(Hat tip: SenateUS)