A group created to stop construction of a grade-separated interchange at Rio Road and U.S. 29 intensified its campaign Thursday by claiming that traffic volumes are not growing fast enough to justify the $84 million project.

“Peak hour traffic trends are actually going down,” said Dexter Williams, a traffic engineer hired by Smart29 to review previous studies sanctioned by the Virginia Department of Transportation.

One of those studies was the 29 North Corridor Transportation Study produced by the Thomas Jefferson Planning District Commission. Its authors concluded that a grade-separated interchange was necessary at Rio “to allow traffic to operate effectively in the southern half of the corridor.”

That study is the backbone of the transportation component of the Places29 Master Plan, which calls for a series of roads parallel to U.S. 29 as well as several grade-separated interchanges to relieve congestion in Albemarle County’s main growth area.

Williams, a Richmond-based engineering consultant who specializes in traffic and development, said in an interview that the traffic increases predicted in the study did not come true.

“They forecasted an 80 percent increase from 6,500 vehicles an hour entering the intersection [in 2005] to over 12,000 [in 2025],” Williams said. He said actual traffic counts conducted as part of the Route 29 Solutions process are actually down at the location.

Using VDOT’s traffic modeling software, Williams estimated that the Rio Road interchange will only save motorists in 2018 less than a minute of travel time on the 3.3-mile stretch between Hydraulic and Polo Grounds roads.

“It’s very expensive for what you get,” Williams said.

VDOT engineers said they were not prepared to respond to his claims.

However, a member of the Route29 Solutions Project Delivery Advisory Panel said he had a hard time making sense of Williams’ work.

“Their main point seems to be that Route 29 is working just fine as it is,” said Morgan Butler, a senior attorney with the Southern Environmental Law Center. “But the fact remains that the Rio intersection is already in bad shape, and we can’t afford not to fix it before the parallel roads are completed.”

The interchange is part of a $230 million package of improvements recommended this spring by former VDOT Commissioner Philip A. Shucet with input from a series of stakeholders along the greater U.S. 29 corridor. Many of projects were called for in the Places29 Master Plan, which was adopted by the Albemarle County Board of Supervisors in February 2011.

All of the projects were funded by the Commonwealth Transportation Board as alternatives to the now-defunct Western Bypass of U.S. 29. The Federal Highway Administration signaled in February that it would need additional studies of the benefits of the bypass before allowing the 6.2-mile, four-lane highway project to move forward.

A chart VDOT engineers used in 2012 as a part of an environmental assessment of the bypass indicates that motorists traveling through the Rio Road intersection experienced an average delay of 156 seconds per vehicle during afternoon peak periods.

Traffic projections indicated that the delay would increase to 312 seconds per vehicle in 2040 if neither the bypass nor the Rio Road interchange were built.

The Rio Road project is fully funded, and the Commonwealth Transportation Board is set to award a contract in February to a firm to design and build the interchange, a $54 million widening of U.S. 29 and a $51 million extension of Berkmar Drive to Hollymead Town Center.

In a related project, the city of Charlottesville plans in a separate project to build a nearly milelong extension of Hillsdale Drive between Whole Foods and the Senior Center.

Smart29 members are asking for VDOT to delay the interchange until those other projects are built first.

“We believe the parallel roads are the most important part of this package,” said David Mitchell, an engineer with the Great Eastern Management Company. He added he is concerned those projects might have their funding raided if the cost of the interchange increases.

Mitchell said the interchange will hurt businesses in its vicinity during and after construction.

“We think the interchange is detrimental in a lot of ways because of loss of access, loss of visibility as you go through the tunnel and won’t be able to see the businesses,” Mitchell said.

Williams’ information was released the same day the delivery panel met.

At the meeting, Shucet said his job was to help make sure all of the projects are built by the end of October 2017. A new governor will be elected the following month.

The next administration likely will decide the fate of a second grade-separated interchange at U.S. 29 and Hydraulic Road. Officials have allocated $10 million to pay for a study of that potential project, but its eventual construction is far from guaranteed.

That prompted questions from skeptical panelists.

“Why build the grade-separated interchange at Rio if the long-term plan isn’t to do the expressway all the way down 29?” asked John Nunley, an owner of Better Living.

Shucet said he was confident the grade-separated interchange would improve operations at Rio Road, despite Williams’ claims.

“It is not unusual to grade separate an intersection that is congested,” Shucet said.