Toll lanes planned for part of the Capital Beltway and Interstate 270 in Maryland would not alleviate traffic congestion in the regular lanes during the evening commute without other improvements to both highways, according to a state study released Friday.

By 2045, the analysis found, motorists would average a 7 mph creep on the Beltway’s inner loop between the George Washington Memorial Parkway and the I-270 spur — the same slog as if the toll lanes were not built. Those in the toll lanes would average 23 mph — faster than the regular lanes but far below the minimum of 45 mph promised by state officials.

The findings appear to contradict state transportation officials’ assertions that adding toll lanes would benefit even those motorists who could not afford — or did not want to pay — the tolls. State officials have said the regular lanes would flow more freely because some vehicles would move into the toll lanes.

The study also appears to undermine the Maryland Department of Transportation’s goal of alleviating highway congestion between job centers in Northern Virginia and the Maryland suburbs. The continued evening slowdowns in the regular lanes would hit Maryland commuters who already head home from Tysons and the Dulles corridor through some of the region’s worst backups.

The congestion would be the result of bottlenecks that would occur where the toll lanes end and merge into regular traffic at the Beltway’s I-270 spur and on I-270 near I-370, the study said.

Among the study’s other findings, vehicles in the regular lanes of northbound I-270 in the evenings would move at an average of 28 mph — about the same as the 29 mph speeds they would encounter without toll lanes absorbing some traffic. Toll lane traffic would move at an average of 37 mph, which is faster than the regular lanes but more slowly than the minimum 45 mph envisioned, the study said.

Terry Owens, a spokesman for the MDOT project, said the traffic analysis assumed no Beltway upgrades east of the I-270 spur. However, he said, state officials have known that, without additional improvements, traffic would grow worse in the non-widened part by 2045, especially at the chokepoint between Connecticut and Georgia avenues.

“We must provide some improvements for traffic relief on that top side location over the next 24 years” Owens said in an email.

Such improvements could come from ramp metering, extending or connecting entrance and exit lanes, and dynamic signs directing motorists to alternate routes, he said. What would be done — and when — would be determined by a separate study with input from local officials and the public, he said.

The study, based on regional computer traffic models, is likely to fuel criticism from toll lane opponents who have said creating the lanes would not be worth harming streams and public parkland or increasing vehicle emissions.

Ben Ross, of the Maryland Transit Opportunities Coalition, said it makes sense that traffic would back up where the toll lanes would merge into the rest of the highway. However, he said, the analysis seemed “fundamentally flawed” in other aspects, such as by showing that peak evening congestion would improve on the inner loop between I-270 and I-95 if the toll lanes were built, even though that section of the Beltway wouldn’t be widened.

“It’s simply not credible,” Ross said.

MDOT decided to end the Beltway lanes at I-270 and postpone expanding the top and eastern sections at the request of local officials and community activists who said it would destroy too many homes and too much environmentally fragile parkland. State maps show that section of the Beltway as “future phases” of the toll lanes plan.

Under the plan, I-270 north of Rockville would be widened after toll lanes opened on the lower section because the federally required environmental study for the northern part to Frederick has lagged.

MDOT had to update its federally required draft environmental impact statement released in July 2020 to account for changes that would stem from its decision to end the Beltway toll lanes at the I-270 spur, rather than continue them to Route 5 in Prince George’s County.

Toll lanes would be more effective at reducing congestion in the peak direction, toward Northern Virginia, during the morning rush, the study found. Vehicles in the regular lanes of the outer loop heading from I-270 and across the American Legion Bridge would travel at an average of 52 mph, up from 33 mph if the lanes weren’t built. Motorists in the toll lanes would average 56 mph.

On southbound I-270, morning speeds in the regular lanes would average 50 mph between I-370 and the Beltway, up slightly from the 46 mph estimated if the toll lanes weren’t built. The southbound I-270 toll lanes would flow at 58 mph, the study said.

Morning traffic headed toward the American Legion Bridge probably would improve more because the toll lanes would connect to Northern Virginia’s more extensive network of tolled express lanes. By then, they would extend from the American Legion Bridge and down the Virginia side of the Beltway to Interstates 95 and 395, as well as on I-66.

Edgar Gonzalez, head of the pro-toll lanes Suburban Maryland Transportation Alliance, said the state could improve the inner loop to alleviate any evening backups from the merging toll lanes.

For example, he said, the state could extend part of the toll lanes’ merge area to move traffic more quickly beyond the crowded I-270 spur. Correcting the northbound I-270 evening bottleneck would require extending the toll lanes to Frederick as quickly as possible, he said.

“The good news is they’ve identified where the problems could be,” said Gonzalez, a former top Montgomery transportation official.

Montgomery County Executive Marc Elrich (D), who has opposed the MDOT plan, said the findings prove the state isn’t doing enough to reduce traffic by expanding mass transit options. The state should do more to divert traffic from the top of the Beltway to the Intercounty Connector (ICC) farther north, he said. I-270 could be improved more quickly and equitably, he said, by adding two non-tolled lanes that would be reversible in the peak direction.

Ending the first segment of northbound toll lanes on I-270 at I-370 would be “nuts,” he said, adding: “Any time you shrink the number of lanes on a road like that, it’s going to be hell.”

The analysis found more positive effects of the toll lanes on the overall highway system and major arterial roads. In the morning rush, the average delay per vehicle systemwide would drop from 12.9 minutes to 10.6 minutes, or 18 percent, the study found. In the evening, the average delay per vehicle would be 9.2 minutes — four minutes less, or a 32 percent drop.

Another potential benefit: Delays specific to local roads would be reduced by 3.5 percent because faster-moving parts of the highways would draw traffic off them, the study found. However, it said, there would be “some localized increases in arterial traffic” on roads near the toll lane interchanges.

MDOT recently selected a private consortium, led by Australian toll road operator Transurban, to develop the toll lanes’ design at its own expense while pursuing a 50-year contract to build the lanes and finance their construction in exchange for keeping most of the toll revenue. That long-term contract would be valued in the billions of dollars, making the 12-mile Maryland project one of the largest public-private partnerships in the country.

The state study, which is required for federal environmental approval, is occurring simultaneously with the private consortium’s design work.

Maryland Gov. Larry Hogan (R) has made the toll lanes plan his signature infrastructure project, saying it would alleviate chronic and worsening traffic congestion and keep the Maryland suburbs economically competitive.

Bridge experts also have determined how to rebuild and widen the American Legion Bridge in a way that would cause less damage to National Park Service land on both sides of the Potomac River below, the report said.

Under the plan, trucks and heavy equipment would reach the bridge construction site only from the north side of the river along the Clara Barton Parkway. They would use a new, temporary bridge across the C&O Canal and a temporary haul road parallel to the C&O Canal towpath, a popular walking and cycling trail.

Doing so, the study said, would protect 7.8 acres of land near the GW Parkway and 5.3 acres of the Chesapeake & Ohio Canal National Historical Park. It also would spare most of Plummers Island, a 120-year-old research site for the Washington Biologists’ Field Club, which has said the 12-acre island is critical to long-term studies of plants, insects and wildlife. Experts for MDOT reduced the effects to the island by 90 percent, to two-tenths of an acre, where a pier piling would be built for the wider bridge, the study said.

The study also confirmed MDOT’s earlier commitment that the Beltway’s widening would spare a historical African American cemetery in Cabin John.

The public may comment on the updated study before the Nov. 15 deadline via the state’s project website or by sending an email to oplanesMLS@mdot.maryland.gov.