PHOENIX >> A wrong-way collision on a Phoenix freeway killed two university students and a young adult today in the latest in a string of head-on wrecks on Arizona highways.

A 22-year-old man driving a car with Colorado license plates on the wrong side of the freeway slammed into a vehicle carrying two women, ages 19 and 20, at about 2 a.m., said Arizona Department of Public Safety spokesman Raul Garcia.

Authorities have been seeing a spate of wrong-way wrecks on Phoenix freeways in recent years, with drug and alcohol use typically the main culprit. Authorities have responded to seven wrong-way wrecks with injuries or deaths statewide so far this year, compared to nine for all of last year, said Trooper Kameron Lee, another Arizona DPS spokesman.

State officials are trying to find ways to prevent the crashes, most of which happen on the web of freeways that weave through the Phoenix metro area.

Garcia said the identities of those killed in the wreck weren’t immediately available. But Grand Canyon University spokesman Bob Romantic said two of those killed were students at the private Christian university and that they were in separate vehicles involved in the crash on Interstate 17.

Romantic said the university, out of respect for the privacy of the families, would not be releasing information about the students. The car carrying the two women, believed to be sisters, had North Carolina license plates.

Arizona troopers were working with Colorado and North Carolina authorities to notify relatives, Garcia said.

It’s not immediately known whether the wrong-way driver was under the influence of drugs or alcohol, and that will be determined by toxicology tests conducted by the Maricopa County Medical Examiner’s Office, Garcia said.

In an effort to keep drivers on the right side of the freeway, the Arizona Department of Transportation has installed hundreds of larger and lower “wrong way” and “do not enter” signs on more than 100 freeway ramps.

The agency plans later this year to install a pilot detection and warning system on Interstate 17 and ramps, agency spokesman Steve Elliott said.

The system will send alerts to law enforcement and transportation department traffic operators, post warnings on overheard message boards, provide location updates on wrong-way drivers and trigger flashing warning signs at exit ramps to try “to get the wrong-way driver to self-correct,” ADOT said in a statement.

“Ultimately, engineering, along with enforcement, can be only one part of the response to wrong-way driving because this is first and foremost a driver behavior issue,” the statement said.

ADOT began planning the pilot project in late 2015 following a rash of wrong-way crashes, including ones that killed an off-duty Mesa police officer and a young Mesa couple.

The Department of Public Safety regards wrong-way driving primarily as a societal problem, Garcia said.

“We want the public to take responsibility” to not get behind the wheel if impaired and to keep others from driving if they’re impaired, he said. Alternatively, “if they can’t take those keys away, dial 911 so we can take those keys away.”

He also said drivers should stay alert, avoid distractions and plan how they would respond in a split second to a hazard such as an oncoming wrong-way vehicle.