An airports authority official sought Wednesday to discredit allegations by a former board member that the authority was relying too heavily on fees from Dulles Toll Road users to fund the $6 billion Silver Line.

Bob Brown, a former chairman of the Metropolitan Washington Airports Authority's finance committee, claimed in a letter earlier this month that the financing plan for the Dulles Rail project was "fundamentally flawed."

"The steady climb in toll rates ... will now accelerate. The rate-making will lay bare the truth about the plan of finance, and the burden it places on Virginia motorists," Brown wrote.

But Conner said Wednesday that Brown's letter was unauthorized and did not reflect the views of the airports authority.

"Those are pretty damning allegations and pretty surprising given the author of the letter was intimately involved in developing the financing plan," Conner said.

Conner said a bond investor called him Tuesday, worried about Brown's letter.

Conner disavowed Brown's claims, though he said Wednesday that he had his own concerns about increasing the tolls to pay for the rail project.

"We really are in good faith looking at all alternatives," he said.

Also on Wednesday, the airports authority revealed that five firms are in the running to build the second phase of the Silver Line, taking it from Reston, past Dulles International Airport and into Loudoun County. The contract is worth between $1.4 billion and $1.6 billion and will likely be awarded in May 2013, with construction starting in July 2013, officials said. Officials estimate the line will be complete in 2018.

The five teams vying for the contract are made up of the following companies:

1) Bechtel Infrastructure Corporation

2) Clark Construction Group LLC; Kiewit Infrastructure South Co.

3) Archer Western Contractors LLC; PCL Civil Constructors Inc.; Corman Construction, Inc.

4) Skanska USA Civil Southeast; Granite Construction Company; G.A. & F.C. Wagman, Inc.; Trumbull Corporation; Facchina Construction Company, Inc.

5) Fluor Enterprises, Inc.; Tutor Perini Corporation; Stacy and Witbeck, Inc.