Congestion levels on metro-area highways and freeways rose a scant 0.3 percent over the past year as additional travel lanes helped mitigate rush-hour traffic snarls, but the relief might be short-lived.

Drivers encountered congested roads 23.7 percent of the time between 5 and 10 a.m. and 2 and 7 p.m. weekdays last year, a number similar to levels seen in 2015. But the forecast calls for freeways and highways to be clogged as much as 30 percent of the time during rush hour by 2028, according to the Minnesota Department of Transportation 2016 Metropolitan Freeway System Congestion Report released Wednesday.

"We can't build our way out of congestion," said Brian Kary, MnDOT's Director of Traffic Operations. "In the short term, we've seen some improvement on some key corridors, but as we build more general lanes they will become congested. We will see an upward climb of congestion."

MnDOT defines congestion as when speeds are below 45 miles per hour, regardless of the posted speed limit.

Congestion levels measured in October 2016 were compared with those in October 2015. For its annual congestion reports, MnDOT uses October, since the month reflects regular patterns of traffic, when school is back in session, most summer road construction is completed and weather conditions are generally favorable, Kary said.

Last summer MnDOT opened additional lanes on Interstate 494 through Plymouth and Maple Grove and finished a reconstruction project on Hwy. 100 through St. Louis Park. MnDOT also opened a MnPass lane on I-35E between downtown St. Paul and White Bear Lake.

Even with additions to the system, bottlenecks were most likely to form in the mornings on eastbound I-94 and southbound I-494 in the northwest metro, where traffic flow was below 45 mph for more than three hours a day. Other choke points included eastbound I-94 at the Lowry Hill Tunnel, northbound I-35W from Burnsville to Bloomington and both directions of the Crosstown Hwy. 62 between I-35W and west of Hwy. 100.

Congestion was more prevalent in the morning, when 202 miles of roads were congested for at least one hour or more. In the evening, the number of miles that saw congestion of one hour or more fell from 167 miles to 157 miles, but drivers stuck in traffic were caught for longer periods of time, the report said.

A few of the worst afternoon bottlenecks included I-494 through Bloomington, southbound I-35W from downtown to the Crosstown and northbound I-35W from Roseville to I-694 in Arden Hills and northbound Hwy. 169 through New Hope.

The Met Council estimates that the metro area could add as many as 800,000 residents by 2040. Kary said even a 5 percent increase in vehicle traffic can result in a substantial congestion growth, while similarly a 5 percent drop in vehicular traffic could keep drivers moving.

Going forward, he said, MnDOT will be looking at more projects that encourage people to take transit or carpool rather than adding more lane capacity.