Four people including a child were taken to a hospital Saturday after a concourse train at Denver International Airport malfunctioned, jolting passengers when the train abruptly accelerated and then decelerated as it approached a platform in the main terminal.

Airport spokesman Heath Montgomery said the train was carrying about 45 passengers when the accident happened about 2 a.m. Montgomery said 27 passengers were checked out by medics and refused treatment and the others were not injured.

Dan Weaver, a spokesman for University of Colorado Hospital, said he could not provide conditions on the passengers or the extent of their injuries.

Montgomery said the train was coming around a corner when a sensor malfunctioned, causing the train to accelerate. He said another sensor caught the problem and immediately slowed the train down.

"My understanding is that most of the passengers were standing on the train when it jolted, and they were not expecting it," Heath said.

The airport is expecting about 1.1 million passengers this week because of spring break, but he said traffic was slow because there were few overnight flights.

"It could have been worse if it was in the middle of the day," Montgomery said.

He said one track switch was slightly damaged, but it did not affect passenger safety and the four cars involved were replaced. The shuttle trains were back in service later Saturday.

He said the trains are run by a contractor, which was notified and fixed the software problem.

"They are confident in the safety of the system, otherwise we wouldn't operate it," Montgomery said.