As action picks up in the House and Senate on differing versions of a multiyear surface transportation bill, House Republicans have sparked a major fight by proposing to cut mass transit's 30-year-long link to Highway Trust Fund financing.

After months of false starts, delays and small advances, congressional committees have stepped up the pace on the highway-transit bill. With more than $50 billion a year in construction aid at stake, the bill is the industry's top legislative priority.