Expansion of I-93 to six lanes could move buildings in Concord

Monitor staff
Published: 12/12/2016 7:50:30 PM

Concord’s ugliest public face – the stretch of downtown facing Interstate 93 – might get a makeover soon as part of a long-planned expansion of the interstate highway to six lanes through the city.

Widening I-93 and improving the confusing traffic flow around exits 14 and 15 could involve a number of changes to the portion of Concord near the highway, according to options being considered by the state Department of Transportation. Depending on how the highway is reconfigured, possibilities include removing parts of the Capitol Shopping Center – particularly the back of Burlington Coat Factory; removing buildings around the Ralph Pill Marketplace; shifting the Pan Am Railways line; moving the Unitil electric substation alongside Loudon Road; or altering parts of Stickney Avenue.

These would be needed to make room for a wider highway and various approach ramps within a “pinch point” created by the proximity of the Merrimack River to city developments, said Gene McCarthy of the engineering firm McFarland Johnson. He has been working for more than a decade on proposals to expand the roughly 4 miles of highway between its intersection with I-89 at Exit 12 and I-393 at Exit 15.

“These all have different levels of impact,” McCarthy said Monday as he presented a slew of possibilities in an hourlong presentation to the Greater Concord Chamber of Commerce.

The presentation is part of a series of programs the state is running to help it rule out some options to a single plan that would be presented at public hearings before the end of the upcoming summer.

“We want to know what exactly do you like, what don’t you like? Is something missing?” he said of the options. The state hopes to have narrowed down choices by the end of the coming summer and put them forward for public hearings, so it “can move forward with the process.”

Under the schedule for work in the state’s 10-year highway plan, actual construction wouldn’t begin until 2024 at the earliest, preceded by years of engineering and obtaining rights of way.

The entire project is likely to cost in the range of $200 million. A total of $61.4 million is included in the 10-year plan through 2028, about $46.5 million of which is for actual construction starting in 2024.

Interstate I-93 was expanded to six lanes south of Concord many decades ago, and as McCarthy explained it, in the early 2000s, work plans began to continue the widening north. Originally, the idea was to go beyond six lanes, but traffic counts and expected growth slowed after the Great Recession and adding a single lane in each direction is now seen as suitable.

The total expansion is likely to include some associated work outside the highway, such as revamping Exit 1 on I-89 that connects with Logging Hill Road in Bow.

As McCarthy explained it, much of the cost and effort involved with expanding the highway occurs because this stretch of road has too many exits that are too close together, causing what traffic engineers call “deficient weave,” the syndrome when cars are trying to merge onto or off of a highway when they don’t have enough room.

“This where the challenge of (the) project is. From 89 all the way to 393, there’s about 5 miles total of roadway and we have seven full access interchanges. That’s quite a few ... certainly beyond what is recommended.” he said.

Among the issues that the project will have to face are replacing the bridge that carries I-393 over I-93 – which is high on the state’s tally of “red-listed” bridges because of the amount of traffic involved as much as the condition of the bridge – and coping with the line of commuters that back up from Loudon Road onto I-93 during rush hour. That problem might be fixable in the short term by replacing a stop sign at Loudon Road with a stop light.

The project’s big problem, however, is the confusing proximity of exits 14 and 15, compounded by the “pinch point” between the river and Burlington Coat Factory.

“This is where things get interesting. There’s a lot going on there,” McCarthy said. His discussion about possibilities included such geometries as a “diverging diamond intersection,” and a “clover stack,” which is like a partial cloverleaf with fly-over lanes and is “not something you see in this part of the country very often.

Details of all the options can be seen here.

(David Brooks can be reached at 369-3313 or dbrooks@cmonitor.com or on Twitter @GraniteGeek)

David Brooks bio photo

David Brooks is a reporter and the writer of the sci/tech column Granite Geek and blog granitegeek.org, as well as moderator of the monthly Science Cafe Concord events. After obtaining a bachelor’s degree in mathematics he became a newspaperman, working in Virginia and Tennessee before spending 28 years at the Nashua Telegraph . He joined the Monitor in 2015.

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