UPDATED | November 10, 2015 5:30 PM

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DALLAS (CBSDFW.COM) – A North Texas man died as he and another man tried to prevent an accident on a Dallas freeway Tuesday morning.

The Dallas County Sheriff’s Office identified the man killed as Brenton K. Smith, 24, of Krum.

Deputies say Smith’s Dodge Ram pickup experienced a mechanical problem, causing him to lose control. The driver hit the median on I-35 South, near the exit for Inwood Road. The vehicle then came to a stop in the center lane.

It was 5 a.m. and dark outside. Marcus Dennis, an off-duty security guard, happened to be driving by when he saw the crash. Dennis pulled over to try to help Smith. “He was more concerned about trying to get his truck out of the road, before something like that happened.”

Dennis says an 18-wheeler appeared to not see them, and came very close to hitting the two. At the last second, the big-rig swerved. Right behind it was a DART bus.

The bus side-swiped the pickup and struck Smith, just as Dennis jumped out of the way.

“The DART bus driver could not have slowed down. There was nothing he could do to prevent the situation. If the truck ahead of him had tried to slow down like I was signaling for him to do, this would have been a different outcome,” said Dennis.

A DART spokesperson says the bus driver had been with DART since 1989. The bus was empty as the driver had just left the depot to begin his morning route.

“He was really distraught and hurt about the situation,” said Dennis.

Deputies say the driver of the 18 wheeler did not stop. Authorities do not expect to file any charges.

Smith was a US Army veteran. He was also married, living in Denton County with his wife.

The Army Times reported that Smith was promoted to Staff Sergeant in April of 2013. According to the Denton Record Chronicle, he graduated from Lake Dallas High School in 2009.

Dennis says knowing the military serviceman died, the day before Veterans Day, made him sad. “I would like for his family to know that he was more worried for others than himself.”