CASTLE ROCK — An 11-year veteran of the Colorado State Patrol was struck by a tractor-trailer and killed Friday afternoon on Interstate 25 just outside of Castle Rock, becoming the third state trooper to be fatally hit by a vehicle in the line of duty in the past 18 months.

Trooper Cody Donahue was outside of his patrol car and investigating an unrelated crash in the interstate’s northbound lanes near Tomah Road when the tractor-trailer slammed into him.

Authorities say they have detained the truck’s driver, who will likely be arrested and charged. The driver’s name and other identifying information have not been released.

“This is an incredibly sad day, one that we are seeing way too frequently,” Division Chief Steve Johnson, of the Douglas County sheriff’s office, said during a news conference. “When you see these troopers and you see these law enforcement officers just trying to do their job, just please move over.”

UPDATE: @CSP_News confirms state trooper was killed in collision with truck. Highway closed indefinitely. #COTraf pic.twitter.com/LzLbTbYlGL — CBSDenver (@CBSDenver) November 25, 2016

Johnson said there are “children that no longer have a father; a wife that no longer has a husband.”

The northbound lanes of Interstate 25 were closed in the area while the Douglas County sheriff’s office investigated the crash.

Officials said the tractor-trailer that hit Donahue belonged to a commercial food service company. Detectives will review cameras aboard the truck as well as from Donahue’s patrol vehicle as part of their criminal probe of the crash.

Television news helicopter images from the scene showed a U.S. Food truck not far from the crash scene and what appeared to be several yellow evidence markers lining the roadway’s shoulder near a parked State Patrol Dodge Charger.

Maj. Steve Garcia, of the State Patrol, said Donahue — who was assigned to the agency’s nearby Castle Rock office — had elementary school-aged children and a wife.

“Cody was a really good kid and he had two beautiful children. … He’ll be really missed,” an emotional Garcia told reporters.

Garcia also called Donahue a reliable team player and asked for the community’s support and prayers.

“We don’t call them accidents for a reason. This was a crash,” said Trooper Josh Lewis, a State Patrol spokesman. “And crashes, especially like this, can absolutely be avoided.”

The collision happened just after 2 p.m. a few miles south of the Plum Creek Golf Course.

A sheriff’s office dispatcher sent deputies to the scene after reading a citizen report about the aftermath of the collision over the law enforcement radio. “An officer was laying in the lanes of traffic,” the dispatcher said, according to recordings captured on Broadcastify.com.

A few minutes later, someone said over the radio: “All units on the officer down: Coroner is being requested.”

The Colorado Department of Transportation sent out a tweet at about 2:30 p.m. saying the interstate was closed at Tomah Road because of police activity. All northbound lanes were closed at Tomah Road, north of Monument, through Plum Creek Parkway.

CDOT photos from the scene showed major delays in the area and motorists being routed off the interstate.

Tow truck is hauling away a banged up patrol car. Trooper was hit & killed by a passing vehicle. pic.twitter.com/adE0dDZJrq — Liz Gelardi (@LizGelardi) November 25, 2016

The trooper’s death is the third in the State Patrol since May 2015.

“It has been a very difficult couple of years,” Lewis said.

Trooper Taylor Thyfault was struck and killed by a fleeing suspect’s vehicle in Longmont on May 23, 2015. In September, Christopher Gebers was convicted of first-degree murder and attempted murder in the collision. The guilty finding carries an automatic sentence of life in prison.

Thyfault was a cadet at the time of the crash, and was posthumously promoted to the rank of trooper.

On Nov. 15, 2015, Trooper Jaimie Jursevics was struck and killed — near where Donahue was hit — by 52-year-old Eric Henderson as he drunkenly drove southbound down I-25 near Castle Rock while heading home from a Denver Broncos game. He was sentenced in June to eight years in prison for the crash after pleading guilty to vehicular homicide while driving under the influence and tampering with physical evidence, both felonies.

Jursevics, 33, who joined the Colorado State Patrol in January 2011 and began working at the agency’s Castle Rock office in 2014, is survived by her husband and daughter, Morgan, who was 8 months old when her mother died.

Donahue is the 27th trooper to die in the line of duty for the Colorado State Patrol since the agency’s inception in 1935.

An official GoFundMe page has been set up by a family member and is accepting donations. This is the only legitimate account online that has been established for the Donahue family, the patrol said Friday night. Donations for Donahue’s family also may be made to the Colorado State Patrol Family Foundation, marked for the Donahue family.