Earmarks have always been great for car-lovers. I'll bet Don Young (R-AK), former chair of the House Transportation Committee and author of the infamous "Bridge to Nowhere," could go on for hours detailing the ways his career on the Hill has been spent advancing the interests of drivers in Alaska.
More importantly, earmarks are a great way to get money away from other things and direct them to cars and roads instead. Case in point: High-speed rail. From the Legislative Fiscal Bureau:
[S]ince the funds were provided by an act of Congress for passenger rail projects, the U.S. Department of Transportation does not have the authority to permit the state to use the grant funds for a purpose unrelated to passenger rail.
To prevent the administrative reallocation of funds and to allow Wisconsin to use the funds for a non-rail purpose, the relevant law would have to be changed to earmark the rail grant funds to the state for an alternative, specified purpose.
The only thing consistent about politics is its inconsistency. Nowhere is that better demonstrated than within the GOP's rhetoric on the federal budget.
This discussion isn't particularly relevant since the Democrats still hold the Senate, and any $800 million earmark would likely be vetoed by the president. But it nevertheless highlights how earmarks empower the legislative branch and take power away from administrators in the executive branch, who small government types proclaim to detest.