In a southbound view, commuters on the Md. Route 175 eastbound interchange barely move, waiting to exit onto northbound I-95, whose traffic crawls toward Md. Route 100. (Karl Merton Ferron, Baltimore Sun / May 1, 2013)

INRIX and the state measure route dependability. Eleven segments of the Beltway, Interstate 695, are in the top 30 statewide for being unreliable in the morning. The number drops to six during the evening commute.

"If the congestion is bad on a good day, God forbid you add rain or snow to the picture. You can double your commute," said Ragina Averella, a spokeswoman for AAA Mid-Atlantic. She added, "For the daily commuter, the reality is if your options are limited and you have to use 695 or 95, plan with the idea that you're going to get stuck in traffic."

The responsibility for finding solutions is shared. Seven of the 10 bottlenecks on the list — including No. 1 — are administered by the State Highway Administration, which maintains roads that carry 70 percent of Maryland's traffic. Two bottlenecks are the responsibility of the Maryland Transportation Authority, an agency that raises its own construction money through tolls at bridges and tunnels. The third controlling entity — by act of Congress — is the National Park Service, which owns 19 miles of the Baltimore-Washington Parkway from Route 175 to Washington.

Before the promise of new gas tax revenue, the SHA was forced to concentrate on preserving bridges and roads to prevent further deterioration, safety issues and short-term fixes to nagging problems, said Administrator Melinda Peters.

Last November, the agency asked the Baltimore Regional Transportation Board to add $6.4 million in federal funds so that it could begin planning "low-cost improvements" to alleviate 14 choke points on the Beltway. The upgrades center on widening the road where possible and adding transition lanes at interchanges.

The SHA spent $18.3 million to replace the eight-lane bridge carrying the Beltway over Liberty Road. This fall, it is expected to complete a three-year, $13.7 million project to replace the Frederick Road Bridge with a wider, higher overpass that also will accommodate future Beltway widening.

An infusion of transportation funding will allow engineers to begin looking at other projects, said Doug Simmons, the agency's deputy administrator for engineering and planning.

For example, by modifying the cloverleaf interchange at Harford Road, Inner Loop traffic entering and exiting the Beltway would no longer have to perform a dangerous weave and merge, Simmons said. That project could begin as early as next spring.

"We think that would make a significant difference, at a cost of $3 million to $4 million, by reducing crash rates and improving traffic flow," Simmons said.

A blueprint of sorts exists. Last year TRIP, a nonprofit organization sponsored by the construction industry, insurance companies and unions, said widening the Beltway and replacing a number of bridges at a cost of $1.2 billion was the third most important infrastructure improvement that could be made in the Baltimore-Washington region.

It also called on Maryland officials to improve access to BWI Marshall Airport by spending $220 million to widen three miles of Route 295 between Route 100 and Interstate 195 and build a new interchange at Hanover Road.

As for the No. 1 bottleneck, the future promises more cars and few solutions.

Between now and 2040, transportation planners project the number of north-south trips between Baltimore and Washington will increase 34 percent. Options to widen the parkway start at $463.5 million.

The state can make all the parkway improvements it can afford from Route 175 north. But the other section — south of Route 175 — is owned by the National Park Service, which has long opposed widening the tree-lined roadway beyond its four lanes.

And it might not matter. A 2011 study by state and federal agencies came to three conclusions: Widened sections would attract more traffic; widened sections would not necessarily be less congested than current conditions; and congestion on a widened parkway in 2040 would be similar to today's conditions.

Allen, who transferred to the region last fall from Naples, Italy, said he has found comfort in listening to National Public Radio and a classic rock station as he endures his commute. And he has words of comfort for his fellow parkway sufferers: "I can assure the people of Baltimore that the traffic is much worse in Naples."