Four years after a scoping study was completed, state planners have begun the second phase in a long process to fix traffic congestion and safety at the Exit 17 Interstate 89 interchange.

Planners from the Vermont Agency of Transportation hosted a public hearing on proposed changes at Chimney Corners earlier this month, summarizing the congestion-easing measures that theoretically won’t be built until 2023.

The plan is to replace the 1960s-era structurally deficient two-lane bridge, adding additional approach and turn lanes and leaving room for bicycle and pedestrian traffic at a cost of more than $30 million, the presentation shows.

The proposal for Exit 17 in Colchester, which primarily serves Milton commuters, is pictured at right with additional turn and approach lanes to ease traffic. (courtesy visualization)

The design considers existing traffic and expected population growth and projects out to 2042 with the nearly-worst conditions, said traffic engineer Mark Suennen of consulting firm VHB.

“Probably on a Friday in July in the afternoon – that’s the kind of condition we’re modeling for,” he said. “You don’t build your church for Christmas and Easter, and you don’t build your Walmart parking lot for Black Friday. We’re not trying to build the highway for that worst hour but nearly the worst hour.”

The project would build new on- and off-ramps for southbound traffic, including a designated right turn lane that would eliminate current conditions: These drivers currently wait at a blinking signal to take a left into oncoming traffic.

Northbound commuters could also have two right- and left-hand turn lanes on the off-ramp—a formalization of the existing “unwritten rule” that drivers hug either the right or left shoulder depending on their travel destination.

“We’re over the theoretical capacity of that intersection. That’s a problem,” Suennen said. “That’s where you see two or three times that you have to wait for a whole cycle of the signal before you can get on through.”

Planners hope the changes will eliminate the two high-crash locations on the bridge. Between 2008 and 2012, there were 48 crashes, 18 with injuries, on the ramps.

Queuing traffic, too, is dangerous, Suennen said. Often, northbound traffic in the p.m. peak hours back up onto the interstate, “a very unsafe condition when you’ve got 60-, 70- 80-mph traffic next to stopped traffic on the shoulder,” he said.

The corridor is the major I-89 access point for Milton, northern Colchester and Grand Isle County, an intersection for the heavily traveled U.S. Routes 2 and 7. VTrans’ data shows the majority of trips start and end in Milton, consistent with the town’s reputation as a bedroom community.

The design would also add six-foot-wide bike lanes, highly desired infrastructure for the road that’s part of the Lake Champlain Bikeway, planners said.

Cyclists coming from the Champlain Islands would cross a southbound onramp via a separated path. Milton resident Peter Lavallee wondered whether this should be re-engineered to make bike travel even safer, possibly with an elevated ramp with a bike tunnel underneath.

Project manager Aaron Guyette of VHB said engineers hadn’t thought of that and agreed “any time you can separate the two, you become safer.”

Milton Statehouse Rep. Chris Mattos (R-Chittenden 10) was among the meeting’s few attendees. He wondered if the engineers could add two right-turn lanes by the Maplefields gas station for southbound commuters.

“That’s a huge backup in the morning,” he said.

Suennen said the two left-turn lanes heading north – which eventually merge to a single lane to head into Milton – would fix that problem.

Mattos’ seatmate, Rep. Don Turner, the Republican minority leader, asked whether the existing bridge will be safe for the next five years. The planners indicated it is and said VTrans would make the call for any emergency repairs should they arise.

Both Lavallee and Mattos asked if the project could be done sooner.

Though Suennen joked that with the “right of amount of money,” progress could be accelerated, Guyette said construction isn’t booked until 2022.

VTrans employee Ken Robie who sat in the audience, said planners have to look at the big picture: Exit 16 in Colchester is due for its “diverging diamond” redesign in 2019 or 2020, the same timeframe Milton commuters will be dealing with the hourglass intersection reconstruction at Route 7, Railroad Street and Middle Road.

Planners emphasized this project is only in the conceptual design phase. Still to come is preliminary and final design before construction can commence.

In the meantime, the cost is only expected to rise: The $30 million price tag is based on 2018 dollars.