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A viewer emailed the Verify team to ask why the Denver Regional Transportation District could launch the R line connecting Aurora to the rest of RTD’s rail system, but the G line, which goes through Arvada and Wheat Ridge, is on an indefinite hold.


The simple answer is the R line is a light rail train that uses different technology and is overseen by a different federal agency than the G line, which is a commuter train.

Light rail trains are, like their name implies, lighter than traditional commuter trains, RTD spokesman Scott Reed said.

They’re used in downtown areas that have frequent stops. The trains can accelerate and decelerate faster than a commuter train, but the drawback is they can’t go as fast.

Light rails trains top out at 55 miles per hour while commuter trains can get up to 79 miles per hour.

The technology that controls the speed of light rail trains has been around for many years, Reed said. That means the Federal Transit Administration doesn’t require specialized testing before a train line can launch.

In contrast, the G line is a commuter train and overseen by the Federal Railroad Administration.

The FRA told Denver it had to use this new technology called positive train control when it asked to build the A and G lines.

“It is a safety mechanism that is designed to make sure trains only travel at the appropriate speeds,” Reed said. “If they exceed or fall below a set range, the train will be slowly stopped automatically.”

The problem is that the new technology isn’t working the way it should at vehicle crossings.

RTD is working to fix it on the A line, but the FRA says it can’t open the G line until it sees progress made on fixing the technology.


While both trains fall under the umbrella of RTD, they’re different types of trains that use different technology and are overseen by different federal agencies.