There are 41 of the new train cars that will run between the main terminal, Concourse A, Concourse B and Concourse C. The new trains move about 850 more passengers each hour than the old ones, and have a 30% improvement in energy consumption, according to the airport.

A spokesperson for DIA told FOX31 in an email that the airport's "automated people movers have a greater than 99.85% availability rate." But what if they stopped working? Would flights be canceled? Is there an alternate option for passengers to walk between concourses in such a case?

Before Monday, passengers with flights in the A gates would have been able to use the A Bridge to get from the terminal to Concourse A, however, the security checkpoint at the A Bridge was permanently closed this week.

So, for the time being, all departing passengers will need to use the train to get between the main terminal and Concourse A. The bridge will be open to all screened passengers after the new East Security Checkpoint opens in 2025.

Otherwise, there is no other bridge or tunnel for pedestrians to get to the other concourses at the airport.

Sometimes there are interruptions in the train service at the airport. According to a DIA spokesperson, the airport works to restore service as quickly as possible and said in most cases, "the system has contingencies that allow operations to continue during troubleshooting."

The spokesperson said that though it's rare for an interruption to occur, there is a plan in case something happens.

"In the rare event of an extended interruption, we have contingency plans in place to bus travelers to/ from our concourses," the DIA spokesperson wrote in an email.

The airport has done this before. In February, the airport paused overnight train service to test the electrical system and make sure the new train cars would work. When that happened, passengers were guided by employees and signs to buses that took passengers between concourses. They also used busses in place of the trains in January when trains were delayed.

There have also been rumors of potential plans to build pedestrian bridges between concourses at the airport. Earlier this year, an artist's rendering was released, showing how a bridge could connect the concourses. No plans were ever made official.

The spokesperson told FOX31 that the airport is " currently exploring redundant options to connect Concourse A to Concourses B and C. We do not have a time estimate on when a decision will be made on a preferred option."