Rep. Jeff Flake (Arizona) has introduced the Resist Offsetting with Additional Debt (ROAD) Act (H.R. 6472). The bill would eliminate funding where there are unobligated balances for earmark projects under SAFETEA-LU, the present transportation funding law. The bill would also prohibit transfers from the General Fund of the Treasury to the Highway Trust Fund.
Shortfalls in the Highway Trust Fund are projected to occur within the next few years. You can find more about this here.