A RISING CHORUS is warning of crippling price increases on the Dulles Toll Road to finance construction of Metro’s Silver Line extension to Dulles International Airport and Loudoun County. Concerns about toll rates and the Silver Line’s prospects are legitimate. Scare tactics are not.

Under a deal struck with Virginia five years ago, the Metropolitan Washington Airports Authority, which oversees Dulles and Reagan National airports was put in charge of building the Silver Line and given control of the toll road in the bargain. The idea was that toll road proceeds would cover more than half the cost of the rail line, now pegged at $5.6 billion, with the remainder coming from the state, the feds, Fairfax and Loudoun counties, and the airports authority itself.

The authority also got the power to set toll rates, thereby ensuring a revenue stream to maintain the road and build the extension. Predictably, rates have risen — in fact, they’ve nearly doubled since 2009 — and will rise more.

That has made the airports authority the target of opponents of the Silver Line extension, mainly Republicans. With plain intent to frighten commuters, critics have warned that round-trip rates, currently $5.50 for a full-length trip on the 13-mile toll road, are projected to rise to $33.

Well, yes, maybe — by 2043, and only if you don’t bother adjusting for inflation.

Rates will rise, and some commuters will be priced off the road. But local leaders have taken steps to mitigate those increases and can take more. At the same time, they will need to continue making the case for the 23-mile Silver Line — a key to Northern Virginia’s future prosperity — even as it nears the halfway point in construction.

A consultant to the airports authority, CDM Smith, projects round-trip toll rates will rise next year by $1, which would cost a daily commuter $250 for the year. That’s a sharp increase, though less than it would be without the $150 million contribution that Virginia Gov. Robert F. McDonnell (R) has pledged to the project this year.

By 2023, CDM Smith has said, round-trip prices could rise to an inflation-adjusted $12.64, more than double today’s rate. That’s expensive, but compared to what? Toll road users now pay less than half the per-mile rate paid by most commuters on the Dulles Greenway and a third less than those on Maryland’s new Intercounty Connector.

The airports authority deserves scrutiny and must maintain transparency. So far, it appears to be doing that. In response to a report by a local citizens association questioning CDM Smith’s numbers, the authority is planning a meeting with the association.

At the same time, the authority must seek other revenue to ease the impact on toll road commuters. It should consider imposing a meals tax on food at the airport, as other airports have done, and fees on airport rental cars. It’s also worth examining a toll on the Dulles Access Road.

Open lines of communication coupled with aggressive efforts to diversify the revenue sources for the Silver Line won’t eliminate the pain of toll rate increases, but they will minimize the flak that could threaten a project that’s critically important to the region.