After two shootings on Interstate 43 in less than a week, Acting Milwaukee County Sheriff Richard Schmidt on Saturday announced he was posting “high-visibility, saturation patrols” in the area.

“Our freeway system is not for outlaw behavior!” Schmidt said in a news release offering the first public accounts of the incidents.

On Friday, a man was shot in the southbound lanes of I-43 between W. Hampton Ave. and W. Capitol Drive at the height of rush-hour traffic, around 4:50 p.m. He was taken to a hospital and is expected to survive.

Police said they were searching for a known suspect. The shooting forced the closure of the southbound highway, causing traffic backups that stretched nearly five miles.

On Monday, a shooting incident caused a crash and shutdown of northbound I-43 near Walnut St. for about four hours.

RELATED:Vehicle struck by bullet during freeway shooting on Milwaukee's I-43

Investigators recovered 19 shell casings from the scene, but no one was reported injured, the Sheriff's Office said.

Witness descriptions of the vehicles involved did not provide specific models, but one was thought to be a red or maroon SUV, and the other a dark-red sedan.

Schmidt described the recent incidents as "thuggish shootings."

“It’s an open investigation, and I’m not going to guess that road rage is the cause in either case until detectives provide details,” Sheriff’s Office spokeswoman Fran McLaughlin said in an email.

But whether the incidents involved criminals shooting for unknown reasons or they were acts of road rage, they’re among many examples of dangerous behavior involving firearms on roads.

Nationwide, the nonprofit group The Trace reported that road-rage altercations involving guns more than doubled from 241 recorded in 2014 to 623 in 2016.

And the two shootings on I-43 weren’t the first for that stretch of highway.

In December 2015, a gunfight erupted through the Marquette Interchange that injured one motorist and damaged several vehicles pierced with numerous bullets.

RELATED:Split verdicts in I-43 freeway shooting, homicide

Motorists who witnessed the shootout told police they saw shots fired from one car at another as both vehicles traveled at a high rate of speed.

In 2013, a shootout occurred on the highway involving a pair of men with concealed-carry weapon permits.

RELATED:2013 freeway shootout case dropped

And in 2014, a crash involving two vehicles near Dean Road escalated when a person in one of the vehicles fired several shots at another vehicle from a short distance.

Not on the highway, in September a road-rage incident turned into an armed robbery on S. 27th St. and W. Layton Ave. after a man whose vehicle was cut off in traffic robbed the other driver at gunpoint.

A Sept. 7 shooting incident, involving two cars, wounded a 30-year-old man washing windows at the Milwaukee Journal Sentinel office building downtown.

RELATED:Man shot washing windows at Milwaukee Journal Sentinel downtown office

Nationwide, at least 38 people have died in a road-rage incident so far this year, including a 2-year-old girl in Memphis, Tenn., who was shot in June, according to The Trace.

“The pace shows no signs of letting up. In the first six months of 2017, there were at least 325 incidents, our analysis of incidents tracked by the nonprofit Gun Violence Archive found — nearly two each day,” The Trace says.

Critics of The Trace say it’s funded by anti-gun advocate Michael Bloomberg, former mayor of New York.

But backers of the right-to-carry a firearm for self-defense also argue that guns, roads and heated tempers are bad chemistry.

“Road rage only happens when there are two aggressive people,” said Tim Schmidt, founder of Delta Defense and the U.S. Concealed Carry Association, based in West Bend.

In any type of altercation, the only time you have the right to use a gun is when “you are in fear of grave bodily harm and are in imminent danger,” Schmidt said.

“Almost by definition, if you are in a vehicle, you have the ability to escape” without pulling a weapon, he added.

A 2006 study of aggressive drivers, by the Harvard Injury Control Research Center, found that drivers with a firearm in their vehicle may be more likely to engage in aggressive driving than those who didn’t have a gun.

Mary Vriniotis, a Harvard researcher who worked on the study, said drivers who felt slighted or endangered may feel the need to react quickly, which can cause a conflict to quickly escalate out of control if someone has a gun in the vehicle.

“If it were true that an armed society is a polite society, then you would expect that nobody would be perpetrating an aggressive behavior if they had a firearm on them, and that they would be assuming that everyone else may have a firearm,” Vriniotis said in a Journal Sentinel interview Saturday.

“Firearms used in road-rage incidents sort of questions the notion that everyone walking around with a gun is somehow more calm or less aggressive than people who don’t have guns with them,” she said.

In Wisconsin, you can carry a loaded firearm in your vehicle if you have a concealed-carry permit.

But that privilege bears heavy responsibility, according to Schmidt.

“When you make the decision to go armed and to live that responsibly-armed lifestyle, you take on additional responsibilities as a defensive driver,” Schmidt said.

“Even if somebody cuts you off in traffic or slams on their brakes and you feel they did it on purpose, if you are carrying a gun you have that additional responsibility to just stand down. Take the high road and let it go.”

Jesse Garza of the Journal Sentinel contributed to this report.