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The carnage started by the State Fairgrounds in Falcon Heights with a head-on crash early Tuesday. Then came a morning rush-hour rollover on the Mendota Bridge that snarled traffic for a couple of hours. That was followed by a crash in which a semitrailer truck hit a pedestrian, causing a 90-minute shutdown of a downtown Minneapolis freeway.

In fewer than eight hours: three crashes, four deaths.

“That’s unusual,” said Lt. Tiffani Nielson of the State Patrol. “Over a long weekend, we might have four to five and we’d consider that high.”

On average, the state records about only one fatal crash a day.

The deaths on Tuesday pushed the number of people who have died on Minnesota roads this year to 127, the same number of people who had died as of this time last year.

And that comes just ahead of the Memorial Day weekend (which is five days later this year than it was in 2015), which is not only the unofficial kickoff to summer, but the beginning of a four-month period when traffic fatalities and serious injuries tend to spike.

“Summer is more dangerous than winter,” Nielson said. “People drive faster when weather is good. People might be feeling good or have plans to enjoy the weather, and speed goes up.”

Deborah A.P. Hersman, president and CEO of the National Safety Council, said drivers can’t take safety for granted in the carefree summer months. “Driving is one of the riskiest things we do every day,” she said.

The first of Tuesday’s deadly wrecks occurred at 3 a.m. when a car driven by David Patrick Hall, 55, of St. Paul, crossed the centerline on Snelling Avenue near the fairgrounds and collided head-on with one driven by Por Vang, 57, of St. Paul, that was heading in the opposite direction, killing himself and Vang. Snelling was closed for three hours.

It’s not clear if speed was a factor in a rollover crash that occurred about 7:23 a.m. in the eastbound lanes on Mendota Bridge. Angelica Serrata, 24, of St. Paul, was at the wheel when her vehicle caught the right-side bridge wall, flipped over and landed on its roof in the left lane, the State Patrol said.

A man who stopped to help said the Toyota Corolla rolled five or six times before it came to rest. A man who was riding in the car was able to climb out of the driver’s-side window, the witness said. Serrata died at the scene. She was strapped in with her seat belt, the patrol said.

Eastbound traffic on the Mendota Bridge was diverted to Hwy. 5/W. 7th Street for a few hours until the crash site was cleared.

Later Tuesday, a 55-year-old man from Minneapolis tried to cross Interstate 94 just north of the Lowry Hill Tunnel. He was hit by a box truck around 10:45 a.m. in the eastbound lanes. It was unclear why the man, who was wearing earbuds, was trying to cross I-94.

Crash reconstruction teams will look at speed and other factors to determine why the crashes happened. They’ll use skid marks, data from black boxes and witness accounts to come up with a cause. In the Mendota Bridge crash, for example, the driver lost control, but why she lost control is part of the investigation.

Officials say speeding and alcohol are the main reasons crashes spike in summer. An improving economy and lower gas prices that have people out driving more also are factors.

Tim Harlow • 612-673-7768