The state transportation department plans to block off Morrisville Parkway at a railroad crossing near the two towns’ border, just west of Chapel Hill Road and the under-construction Park West Village shopping center.

The result: a months- or years-long detour of up to 6.7 miles and 14 minutes, straight through some of Cary’s busiest intersections.

The $16 million construction project would thread the four-lane Morrisville Parkway under the railroad, part of a push to replace railroad crossings with safer bridges or “grade separations.” But it’s not easy to rearrange a rail line and a four-lane road, and Cary Mayor Harold Weinbrecht anticipates the improvements will add to the labor pains of a fast-growing area.

“With Park West building out, with Davis Drive and High House (Road) building out, and then you put this obstacle on the Morrisville Parkway – the people that live in that area are going to be really struggling with transportation,” Weinbrecht said. “For the next few years it’s going to really get bad, I think.”

There are two proposed options for the detour: It’s a question of shorter, sharper pain or more drawn-out delays and congestion.

The state could fully block Morrisville Parkway for two years, reducing costs and safety concerns while finishing construction totally within two and a half years. The alternative is to shut off the crossing for six to eight months, then open a temporary crossing through the construction zone for about two years, resulting in a total construction time of three years.

“The longer you close it, the faster the project will be completed,” said Jamille Robbins, a N.C. DOT engineer public involvement officer. “When you maintain traffic in a construction site, it hinders the construction.”

Karl Thor, of the local group Davis and High House, thinks the project will be a hassle for commuters.

“We already have pretty big traffic problems at Cary Parkway and High House Road. Two years of adding to that before we’ve had a chance to get those intersections fixed is just going to add a lot of time to the commute,” said Thor, an advocate for moderated growth.

Despite his concerns, though, Thor sees little chance the plan will change. The state already has held public hearings to discuss the federally funded project, and it plans to hire a builder by next fall.

The DOT also has heard concerns from residents of the Prestonwood community, which surrounds the Morrisville Parkway crossing.

“This should be a substantial improvement in the quality and safety of the crossing, will eliminate the need for whistle blowing and should enhance property values. However, it appears we can expect a lengthy and disruptive construction process,” resident Regis Rulifson wrote on the neighborhood homeowners association’s website.

Though the detour doesn’t run through Prestonwood, Rulifson wrote, some errant drivers may pass through Prestonwood on Crabtree Crossing Parkway and other neighborhood roads. Some Prestonwood residents have suggested limiting access to the neighborhood.

The DOT now is working out the final details of the plan, including the construction schedule and changes to intersections along the detour. The state could rearrange lane markings in the area and may erect a new traffic signal at Crabtree Crossing Parkway and Morrisville Parkway. Under both detour options, the DOT would ensure that Morrisville Parkway businesses could stay open.

Morrisville Councilwoman Liz Johnson suggests keeping the detour in place for more months in exchange for a shorter overall construction time; Cary staff made the same recommendation.

“I know our staff are working with DOT on the detour to try to make it as easy on the public as possible,” Johnson said. “There’s only so many places, so many alternatives. It’s going to be a short-term inconvenience for a permanent solution.”

DOT officials could announce the final details of the plan in the coming weeks or months.