It begins with an accident that leads to gridlock and inevitably ends with annoyed motorists with frayed nerves recalibrating their GPS in an attempt to find an alternative route.

With an average of 60,000 to 80,000 vehicles a day zipping along Interstate 95 in New London County, even a single lane closure can have massive implications for the municipality serving as the depository for detoured highway traffic.

State police, the state Department of Transportation and local authorities say they are ready with a multi-layered response system is in place to limit the traffic tie-ups and disburse traffic.

The plans, however, do not always guarantee success.

Case in point is a relatively minor incident last Tuesday in which a boat being hauled on a trailer northbound flopped off onto the guide wires of the northbound shoulder of the highway. It was 2:20 p.m. when the incident was first reported to state police in Montville.

The accident led to more than three hours of traffic congestion both on the highway and off, where commuters inundated roads closest to the exits - Routes 12, 1 and 184. Routes 12 and 1 typically handle more than 22,000 vehicles in a day while Route 184 averages about 13,500, according to the DOT.

State police were on the highway calling in a wrecker and crane for the boat while local police posted themselves at major intersections in an attempt to move traffic to the next highway on-ramp in Mystic.

Groton Mayor Heather Bond Somers was on her way to a Town Council meeting that night and exited the highway to run straight into the mess of Route 184. She sat while motorists passed on the right into the shoulder or on lawns to get ahead, "by two car lengths."

"A lot of people clearly had road rage," Somers said.

Somers said she was stuck for 45 minutes before abandoning her original plan to get to Flanders Road and instead headed back to Route 1 to get to the Town Hall Annex.

Groton Police Lt. John Varone said there have been enough accidents on the highway through the years for Chief Michael Crowley to put in place a very clear plan that involves collaboration with state police and any emergency officials from surrounding towns should the need arise. He expects at least one major incident a year.

"The plan is to minimize the number of officers needed to control the intersections and maximize the amount of signage for those who don't know their way around. There's no way around a slow down," Varone said.

Police go out to key locations and override traffic signals, controlling some manually while setting others to flash. All the while, Varone said, police must retain enough control to be able to clear a path for emergency responders.

"It's hugely complicated," Varone said. "It was taking 30 minutes to an hour and a half to travel a stretch that would normally take 10 minutes. You're taking at least two lanes off a limited access highway and putting them on secondary roads. They can only handle so much."

The incident commander at the scene of a highway accident must make the initial judgment call on the length of time it will take and what resources to call in.

State and local authorities follow the 52-page "Unified Response Manual for Highway Incidents in the State of Connecticut." It is essentially a step-by-step guide compiled by the state's Transportation Strategy Board's Statewide Incident Management Task Force that places an incident into a category and calls for responses based on the urgency.

For instance, a Level 3.1 hazardous materials incident would, according to the manual involve an injury, response by fire and rescue personnel and involve two or more lane obstructions, a hazardous spill larger than 25 gallons that requires excavation equipment. The manual says budget two to 6 hours .

The information culled at the scene size-up is disbursed to local authorities and the state Department of Transportation, whose spokesman Kevin Nursick said their priority, along with providing any help they can at the scene, is informing drivers about delays.

Nursick said the DOT incident management is "not a cure, but a treatment for the disease, which is the incident itself - the crash or breakdown."

The real answer would be to have people stop driving erratically, the cause of the majority of incidents. The Manchester man hauling the boat in Tuesday's accident was issued a citation for traveling too fast for conditions. Police said he had slowed for traffic and lost control of his pick-up, causing the boat to roll off.

While the DOT cannot physically stop an accident, Nursick said the next best thing is to keep people informed.

"From the DOT's perspective, we aim to provide travelers with real time traffic information and real time incident notification so they can be aware of the congestion and chose alternate routes."

The network of data collection includes more than 300 traffic cameras around the state, message signs, radar to monitor speeds, two highway traffic control centers manned 24-7 and traffic alerts sent via email and to twitter feeds.

State Police Spokesman Lt. J. Paul Vance said troopers are keenly aware of the problems caused by prolonged closures but "the first and most important thing is caring for the injured. That's the priority."

Some of the other problems contributing to delays are beyond their control - guard rails that need to be repaired, spilled fuel that needs to be cleaned or measurements that need to be taken by the accident reconstruction team.

The fatal crash involving a tanker truck and five other vehicles in 2007 on I-95 in East Lyme was the worst in recent memory. Three people were killed, the highway was closed for an extended period of time and it called on one of the largest emergency responses in recent history with nearly two dozen agencies.

Vance said major accidents are a little more complicated then "getting the broom out and being done with it."

"That in a nutshell is what takes so long," Vance said.

g.smith@theday.com