Toll rates on the Dulles Toll Road will likely continue to rise over the next three years.

In September, the Metropolitan Washington Airports Authority will hold public comment meetings about the proposed toll rate increases.

Aiming to get to a rate of $4.50 per trip by 2015, the proposal would raise per-trip costs by 50 cents next year, to $2.75 per trip, and by 75 cents per year in 2014 and 2015.

According to airports authority staff, this level of tolling is needed to pay off the bonds issued to fund the first phase of the Silver Line, which will extend Metrorail service to Tysons Corner and Reston by the end of 2013. Bonds backed by toll revenues will also be a prime source of funding for the project’s second phase, extending rail to Dulles Airport and into Loudoun County.

“This board will enjoy this particular exercise for many years to come,” said MWAA Board member Frank Connor, referring to the toll-setting process.

Based on an analysis by CDM Smith, the airports authority is projecting that the number of drivers using the Dulles Toll Road will decline as the toll rates climb. The CDM Smith study, commissioned by MWAA, projects a 3 percent decline in toll road transactions in 2013 and 2014, and an 8 percent decline in 2015.

Drivers are more likely to forego the toll road during off-peak hours, said MWAA Chief Financial Officer Andy Rountree. The diverted traffic “will balance among many available alternative routes,” according to a presentation Rountree gave to the board Wednesday morning.

The proposed toll schedule that will be presented at public meetings this fall also includes slightly higher toll rates for trucks with more than two axles, a standard tolling industry practice.

At the request of board member Todd Stottlemyer, the authority staff will advertise truck tolls that are even higher than those staff proposed, due to the additional wear and tear on the roadway from large vehicles. Currently, the highest proposed truck toll for 2013 is $2 more than the rate for passenger vehicles —$4.75 per trip.

The MWAA Board is expected to set the new toll rates in mid-November.

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