Drivers on the Dulles Toll Road may end up paying much less for the Dulles Metrorail project than officials had been predicting thanks to a new funding agreement under which the state and federal governments would make substantial contributions. Tolls are now forecast to climb to $8 for a round trip by 2019, a far cry from the $21.50 round-trip price tag that the Metropolitan Washington Airports Authority predicted would be needed if it didn’t get federal financing.

But officials warned that it’s difficult to accurately predict tolls 10 years out. The current projections are from a 2009 study and a new study will have to be done, officials said.