An uproar over the never-ending roar of traffic on C-470 could put the start this summer of a long-planned expansion of the heavily used highway through Denver’s southern suburbs in jeopardy.

A group of organized neighbors from Highlands Ranch this month filed a lawsuit in federal court against officials with the Federal Highway Administration and the Colorado Department of Transportation for what it says was a “fatally flawed” study of potential noise impacts from the $269 million road-widening project.

The group, the Highlands Ranch Neighborhood Coalition, is asking a judge to stop CDOT from “conducting any further work” on the 12½-mile expansion until it conducts proper noise tests.

The group, which represents around 88 households on the south side of C-470 between University Boulevard and Quebec Street, has long pushed for the installation of sound walls along that stretch.

“For the long-term health, welfare and livability of these neighborhoods, it’s necessary for CDOT to do these noise tests according to their own guidelines,” said Carter Sales, president of the Highlands Ranch Neighborhood Coalition.

Those guidelines, Sales said, require 10 to 20 testing locations. CDOT, he said, used only two.

“I can only conclude they don’t want to know what those results will be,” he said.

But Amy Ford, spokeswoman for CDOT, said the agency’s guidelines require CDOT to do as many measurements as it can to validate its noise model. That is what the agency did last fall, she said.

“And it showed that the noise walls were not necessary, nor would they be effective,” she said. “The process we followed was comprehensive.”

CDOT’s C-470 expansion project calls for adding a pair of tolled express lanes to the westbound side of the highway between Interstate 25 and Colorado Boulevard, a single westbound toll lane from Colorado Boulevard to Wadsworth Boulevard, and a single tolled lane eastbound from Wadsworth Boulevard to I-25.

Two lanes would remain free of charge in each direction. The project is expected to wrap up in spring 2019.