Rush hour traffic is backed up along Interstate 66 in this view from the Vienna Metro Station in Virginia. (Nikki Kahn/The Washington Post)

Despite enthusiasm in Northern Virginia for the state’s landmark Metro funding bill, the plan threatens to exact a higher-than-expected cost in delaying or killing several road projects that would relieve some of the region’s most severe traffic headaches.

The legislation approved by the General Assembly this month would take more than $100 million a year from funds used in the chronically gridlocked suburbs to widen roads, improve intersections and otherwise battle congestion.

The Northern Virginia Transportation Authority (NVTA), the primary agency responsible for planning, prioritizing and paying for such projects, estimates it would lose more than a quarter of its annual revenue in money that the bill diverts to Metro.

Major projects that could be slowed include widening Route 1 in Fairfax County, improving Route 28 in Prince William and Fairfax counties, and widening Route 15 and extending Northstar Boulevard in Loudoun County.

“It’s a lot of money [lost] when you add it up,” said state Sen. Scott A. Surovell (D-Fairfax), whose district includes much of Route 1 from the Potomac River to Stafford County. He estimates that, over 10 years, the cost would be four major road widenings.

In hope of limiting the damage, local officials and lawmakers are pressing Gov. Ralph Northam (D) to propose amendments to the legislation to tap different sources for the money for Metro.

“I’d like to have the governor restore about $43 million” of the total lost under the bill, Fairfax Board of Supervisors Chairman Sharon Bulova (D-At Large) said.

Northam has pledged to try, but he doesn’t have any obvious options.

Republicans in the House of Delegates would seek to block new tax increases. They already killed two out of three tax hikes the state Senate had proposed to pay for Metro.

Northam also could propose to use statewide funds to pay for Metro, but he would face resistance from legislators outside Northern Virginia.

“You’re going to run into a problem from Democrats and Republicans around the state if you do that,” said Del. Timothy D. Hugo (R-Fairfax), who sponsored the House version of the Metro bill. “The best way to get this done is to look for sources in Northern Virginia and to do it without raising taxes.”

Both Northam and Northern Virginian leaders said they would stick to the state’s $154 million commitment to Metro rather than risk sabotaging a regionwide deal. The legislation provides for Virginia to give Metro that amount each year in new, permanent funding on condition that the District and Maryland contribute somewhat larger sums for a total of $500 million.

District leaders pledged last week to give their share of $178 million annually, to be funded in part by an increase in the sales tax and other levies. The Maryland General Assembly will weigh proposals in coming weeks to meet its obligation of $167 million under the plan.

If approved, the regional accord would give Metro dedicated funding for the first time in its history; it is alone among the nation’s major transit systems without a dedicated stream of revenue. The agency has said it needs the money for new equipment and repairs to ensure safety and reliability after decades of neglect and underinvestment.

Despite supporting the bill, Northern Virginian officials hope to lighten the region’s burden, which was higher than anticipated. They had been bracing to give up about $60 million a year from various revenue sources used mostly for roads. Late changes in the legislation widened that by more than $40 million.

That happened primarily because House Republicans blocked tax increases on hotel stays and real estate transactions in Northern Virginia that would have been earmarked for Metro. As an alternative, the final bill diverted from the NVTA to Metro an existing stream of revenue from the real estate levy, known as the grantor’s tax.

“At the very last minute, we learned there had been a change of plans and they were taking away . . . the grantor’s tax,” said Martin E. Nohe, chairman of the NVTA and a Prince William supervisor (R-Coles).

The loss of revenue reduces the authority’s ability to borrow. Nohe said it is too soon to say which projects would be affected, or how, but the results would be significant.

“We already have requests totaling $1 billion more than we were anticipating before the cuts coming from the Metro bill,” Nohe said. “Reduced funds likely mean both slowing down some of our larger projects and funding far fewer of the smaller ones.”

The sole tax increase kept in the final Metro package will increase the cost of wholesale gasoline in Northern Virginia and the Hampton Roads region.

Surovell blamed the loss of road funds on what he called an outdated, anti-tax ideology among some Republicans.

“Our region is being held hostage by this philosophy,” he said.

Sky-high tolls were the only alternative to fix the roads, Surovell said. “If you don’t like $46 tolls on I-66 and $30 tolls on the Beltway, then we have to raise taxes. It’s simple math,” he said referring to the 495 and 66 Express Lanes.

Surovell and some other Northern Virginia legislators voted for the Metro package only after their leaders assured them that Northam would propose amendments to lessen the impact.

One of those was Del. Danica Roem (D-Prince William), a first-term legislator who campaigned heavily on a platform of seeking improvements for Route 28.

Among other effects, the Metro bill would reduce funds available for upgrading the intersection of Route 28 and New Braddock Road in Fairfax by replacing it with a diamond interchange. The $44.7 million undertaking is currently unfunded.

Fixing that interchange “would be a huge deal for my constituents, because they get stuck at that light every day,” Roem said.

Bulova said “the significant hole punched in NVTA revenue” means the intersection project “could very well be delayed, along with a number of other worthy and needed projects.”

Northam has until April 9 to propose changes in the Metro measure.

Said Nohe, “If the governor can find a way to restore the grantor’s tax [revenue] . . . we’re going to dance in the streets on roads that we’ve widened.”