It is the main thoroughfare of the Eastern Seaboard. Constructed in the 1950s, I-95 is one of the nation’s oldest interstates and, at nearly 2,000 miles, one of the longest running north to south.

Truck drivers use it around the clock to carry goods between Florida and Maine. Commuters crowd it morning and night. Local businesses rely on it to funnel customers to them. And in the summer, vacationers fill its southeastern Connecticut lanes on their way to Long Island Sound beaches, Cape Cod and northern New England.

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As anyone who uses it knows, the highway is often crowded to the point of congestion. It widens to three or more lanes in places and narrows back down to two. Accidents, breakdowns and construction can bring miles of traffic to a halt and spill it over onto local roads.

When an accident does occur, which happens on average about 17 times a day on the 112-mile stretch in Connecticut, state police and local emergency responders face challenges reaching the scene, getting any injured people out and rerouting traffic.

Using state and federal data pertaining to highway usage, accidents and safety, The Day has examined I-95’s problems and challenges. Chief among the sources used is the Connecticut Crash Data Repository, 19 years of state Department of Transportation accident data incorporating state police accident reports.

The repository, assembled by the Connecticut Transportation Safety Research Center at the University of Connecticut, shows when and where crashes have occurred on the state’s roadways and records contributing factors such as road and weather conditions and driver behavior.

Reporting by Day staff members illustrates the impact of what the data says about the dangers and frustrations of driving on I-95, including:

Congestion: Widths changing from two to three and briefly to four lanes result in lane-changing as drivers spread out and then have to merge back. Fifty percent of the Connecticut stretch is a two-lane roadway in each direction. About 5 percent is four lanes wide.

Local traffic: The third-highest density of entrances and exits among I-95 states — an average of 1.3 miles between exits — makes I-95 in Connecticut a route for local traffic, adding to the vehicles getting off and on the highway. Only New York and Rhode Island have higher density rates of entrances and exits. Numerous entrances add to drivers’ need to change lanes often.

[naviga:h4]Average miles between exits[/naviga:h4]

[naviga:h6]The shorter the bar, the higher the density of exits.[/naviga:h6]

[naviga:h6]Source:

Federal Highway Administration, Department of Transportation for each state[/naviga:h6]

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Capacity: The 1950s highway was designed to accommodate up to 50,000 vehicles a day, but in some parts now carries 150,000. The most heavily traveled section between 2008 and 2013 was in New Haven. Locally, the heaviest area, carrying about 100,000 vehicles daily, is the Gold Star Memorial Bridge. At the Rhode Island border the number is among the lowest in the state, about 32,000.

[naviga:h4]Average daily traffic (2008-2013)[/naviga:h4]

[naviga:h6]Source:

Connecticut Department of Transportation[/naviga:h6]

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Danger: The number of accidents per year has increased over the 19 years covered by the data, with these five factors judged to be the major contributors: following too closely, improper lane changing, driver losing control, speeding too fast for conditions and an animal or foreign object in the roadway.

[naviga:h4]Most common contributing factors (1995-2013)[/naviga:h4]

[naviga:h6]Hover over each section to see more details for each contributing factor.[/naviga:h6]

[naviga:h6]Source:

UCONN Connecticut Crash Data Repository[/naviga:h6]

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Particularly dangerous sections: Over the 19 years of data, East Lyme from Exit 71 (Four Mile River Road) to the split with I-395 has the highest number of fatalities and injuries in the state east of the Connecticut River: 745, or about a quarter of the crashes that injured or killed. The stretch from Exit 82 in Waterford across the Gold Star Bridge to Groton accounts for another 21 percent. The most dangerous I-95 stretch in the whole state is in Norwalk.

The accident rate for all of I-95 in Connecticut since 2008 is 1.6 accidents per 1 million vehicles. In the area of Exits 71 and 72 in East Lyme the rate is 2.1 accidents per million; in the vicinity of Exits 74 and 75 the rate is 1.8.

Particularly dangerous times: More accidents occur between 3 and 6 p.m.; the worst months are July and August.

Built to pass through cities, the highway twists and turns and goes uphill and down. Its design has remained virtually the same. Numerous bridges and overpasses are due for repair.

As part of a “transformative” $100 billion transportation overhaul for roads, bridges and public transportation, Gov. Dannel P. Malloy has proposed adding a lane along sections of I-95 from New York to Rhode Island to lessen congestion. He also has announced his intentions to rehabilitate the Gold Star Memorial Bridge, which connects New London and Groton, and reconfigure the I-95/I-395 interchange in East Lyme.

Although officially a north-south route, in Connecticut I-95 generally runs east-west. Alternatives are I-84 in north central Connecticut; the commercial, secondary road Route 1; and, for some purposes, rail. The governor’s plan would also enhance public transit options.

Transportation Commissioner James Redeker said the governor’s 30-year plan is unprecedented in the 120-year history of the DOT, but some transportation experts question the solutions proposed for I-95.

[naviga:h3]More coverage[/naviga:h3]

Editorial: Exploring solutions to the I-95 problem