A long-imagined tunnel under Broadway in Littleton is about to become reality.

Littleton officials announced the busy road must undergo a critical infrastructure project, according to a news release, opening up an opportunity for the city to build its long-desired pedestrian underpass below Broadway.

Littleton engineers estimated the cost at up to $9 million, but emphasized it will improve mobility within the south metro Denver municipality — for motorists, pedestrians and cyclists.

Starting in April, traffic along a section of Broadway, just north of Jamison Avenue, will become one lane only in both directions until at least the fall. This is due to the need to replace a culvert line with a durable concrete pipe, allowing water to flow better under the road, according to city officials.

“While digging into a thoroughfare as heavily traveled as Broadway is rare, it also provides an opportunity to tackle a long-desired project: adding a pedestrian underpass beneath Broadway,” Littleton officials said in the release.

The underpass will connect the east and west sections of the Lee Gulch Trail. This offers pedestrians on the east side of Broadway a safer route to the High Line Canal Trail on the road’s west side.

“A pedestrian underpass at this location has been identified for decades as a goal in numerous local planning efforts, including the public-led Broadway Corridor Study and the Littleton Linkages Trail Study, but was generally considered a longshot due to the challenges of major work beneath Broadway,” city officials said.

As is, pedestrians and bicyclists must travel an extra 800 feet and cross the busy Broadway/Jamison Avenue intersection “risking conflicts with vehicles,” officials said.

“At the moment, it’s a particularly tricky trail crossing,” a Littleton spokesperson said of the pedestrian underpass. “It’s been mentioned in various master planning efforts going back at least several years.”

In 2024, city engineers noticed the culvert beneath Broadway north of Jamison Avenue was deteriorating. The Mile High Flood District temporarily stabilized the culvert, but ultimately determined it needs a full replacement “to ensure long-term safety and stability,” according to the release.

Fully replacing the culvert requires digging a 30-foot trench in the road, removing damaged material and replacing it with a concrete pipe.

The work is scheduled to begin in April and end in early fall, while the pedestrian underpass may take until 2026, according to a city spokesperson.

Money for the project comes from South Suburban Parks and Recreation, Arapahoe County Open Space and the Mile High Flood District.

“The City of Littleton is working with local partners to identify funding to complete the underpass project alongside the culvert replacement,” officials said.