Correction: An earlier version of this article incorrectly described a funding breakdown for the Dulles rail project as applying only to Phase 2 of the project. The estimates in the article — 54 percent from road users, 16 percent from federal grants, 4.9 percent from Virginia, 4.1 percent from the airports authority, and the rest from Loudoun and Fairfax counties — apply to the entire project. This version has been corrected.

Users of the Dulles Toll Road will see an increase in rates starting Jan. 1, money that is pledged to go in part to maintain the roadway and in part to fund the new Metrorail line that will extend eventually to Dulles International Airport and Loudoun County.

Rates at the main plaza will go up 25 cents next year. There is no change to the rates at the ramps.

On Tuesday evening, about three dozen people went to a Reston high school to ask questions of staff members of the Metropolitan Washington Airports Authority, which oversees Dulles and Reagan National airports and the construction of the Dulles rail line.

At two dozen informational displays, authority staff members answered questions about improvements — including more overhead lighting, new guardrails and repaired toll booths — that have been made to the toll road. They also were asked about the increased toll rates and how the second phase of the Dulles rail line will be funded.

Some toll road users and watchdog groups are concerned that even higher rates will be imposed eventually — perhaps as much as $17 per round trip — to help pay for the 23-mile, $6 billion Dulles Metrorail line, known as the Silver Line.

Bert Hackney, 42, who lives in Vienna, had one big question about the second phase of the Dulles rail project: “When is it going to start?”

Answer: Construction on Phase 2 is likely to start in 2013.

He also wanted to know which of the six stations on the second phase of the project will have parking. The answer: Four will have parking; only the Reston Parkway and Dulles Airport stations will not.

Jack Boese, a retired lawyer who lives in Reston, said he is concerned that as toll rates rise, fewer people will take the road and more will clog other roads such as routes 50 and 7.

“They’re going to end up raising the toll rates to the point where the well-off business commuter whose time is really money will be the only one using the toll road and anyone with an option won’t,” Boese said. “Route 7 and Route 50 are going to become parking lots.”

The toll increases were agreed to years ago.

In 2009, the airports authority decided to raise toll rates in three stages. The first increase was in 2010, and another took effect this year. The 2012 increase will be the third.

Construction of the first phase of the Dulles project, which runs through Tysons Corner to Reston, is underway and is expected to be completed late next year.

Until recently, it was not clear how the second phase of the Dulles rail project, from Wiehle Avenue to Dulles Airport and Loudoun County, would be paid for. Last month, U.S. Transportation Secretary Ray LaHood helped broker a deal on financing the estimated $2.8 billion Phase 2 project.

Nearly 54 percent of the cost of the entire project is expected to come from Dulles Toll Road users. An additional 16 percent is to come from federal grants, 4.9 percent from Virginia, 4.1 percent from the airports authority, and the rest from Loudoun and Fairfax counties.

The counties have said they are trying to pursue public-private partnerships to help pay for stations and parking garages.

Phase 2 of the rail project became embroiled in controversy over whether to place the station at Dulles Airport aboveground or underground. Eventually, the authority’s board agreed that the station would go aboveground, the less costly option.