Simulation shows a single light-rail car operating on Downing Street within the traffic lanes as part of the proposed Central Corridor Extension.

The smallest FasTracks corridor is less than a mile long, but it makes the connection between the RTD’s original light rail line and the proposed commuter rail corridor to Denver International Airport.

The Central Corridor Extension would run for nine-tenths of a mile up Downing Street from the original station at 30th Avenue to a new joint station with the East Corridor trains along Blake Street at 38th Street, where transfers could be made to the airport train.

The details are in an environmental evaluation on the estimated $67.3 million project that RTD released last month. You can read the entire document here. The transit agency is accepting public comments on it until Monday. You can fill out an online comment form here.

Single light-rail cars would run up and down Downing in traffic lanes with automobiles, like a streetcar system, unlike the layout of the rest of the downtown light rail tracks, which have an exclusive lane along California, Stout and Welton streets.

That means the Central Corridor Extension can be built without requiring any new right-of-way or property acquisition. It requires elimination of about 40 percent of the curbside parking along Downing, but that is less of an impact than giving the light rail its own lane.

Aerial photo shows the configuration of Downing Street from the existing 30th Avenue station northward, with light rail tracks embedded in the traffic lanes.

The proposal also includes two new stations, at 33rd and 35th streets, along with the new end-of line station at Blake.

Trains would operate on the same 15-minute schedule they now have, but RTD proposes to reconfigure the route. Instead of serving Five Points with the original D Line light rail, the Central Corridor Extension run on a loop every 15 minutes from the Blake station, down Downing, through Five Points on Welton and then through downtown on the loop along 19th, Stout, 14th and California streets.

A liight rail train waits at the Downing Station before starting a southbound trip.

The Central Corridor Extension has gone through several proposed alignments and alternatives, along with delays while RTD completed the environmental study on the East Corridor. At one time, RTD considered making the Welton line part of a streetcar loop that would have connected the new Blake station with Civic Center Station at Broadway and Colfax Avenue.

It also considered using low-floor streetcars – different vehicles from the light rail cars – on the line.

But cost considerations led the FasTracks team to propose using single light rail cars, which RTD already owns, for the new service.

Because the Central Corridor Extension is locally funded and doesn’t rely on federal grants, RTD was under no obligation to do a study. But the board several years ago decided to subject all of the 10 FasTracks corridors to similar levels of environmental study and efforts to mitigate impacts.

Map shows the proposed Central Corridor Extension north from 30th Avenue to Blake, and running through the existing downtown loop to 14th Street.