A Washington-based nonprofit research group issued a report Monday that confirms what motorists who travel I-95 in the summer know all too well — Connecticut’s interstate highways are wicked busy.

They are, in fact, among the most congested in the United States, and their bridges are among the most deteriorated, according to the group, TRIP, which assessed the nation’s 60-year-old Interstate Highway System.

The report found that among the 50 states, Connecticut’s urban interstates have the third-highest rate of vehicle travel per lane mile and are the eighth-most congested. Traffic on 60 percent of the state’s urban interstates experiences significant delays during peak hours.

Seven percent of Connecticut’s interstate bridges are structurally deficient, the fifth-highest rate in the nation, TRIP found.

Nationally, 43 percent of urban interstates are considered congested, with California ranking as the most congested. Rhode Island (No. 4) and Massachusetts (No. 6) have a greater percentage of congested interstate miles than Connecticut.

California also ranks as the state with the busiest urban interstates in terms of vehicles per lane mile. Rhode Island ranks fourth, right after Connecticut, and Massachusetts is 10th.

At 15 percent, Rhode Island has the greatest share of structurally deficient interstate bridges. New York ranks fourth at 8 percent and Massachusetts ninth at 6 percent.

The report, “The Interstate Highway System Turns 60: Challenges to Its Ability to Continue to Save Lives, Time and Money,” says interstates face increasing congestion, unprecedented levels of travel — particularly by large trucks — and insufficient funding for repairs and improvements.

According to TRIP, the current backlog of needed upgrades to the system, as estimated by the U.S. Department of Transportation, is $189 billion.

And, while the recently enacted federal transportation program, Fixing America’s Surface Transportation Act, or FAST, provides a modest increase in spending, it lacks a long-term, sustainable revenue source.

By 2020, the annual shortfall into the nation’s Highway Trust Fund will be $16 billion annually, the report says.

“While we celebrate the 60th anniversary of our Interstate Highway System, the record number of motorists using it are all too aware of the need for improvements,” Amy Parmenter, a AAA spokeswoman, said. “If we want to be in a better place down the road, the importance of funding these improvements cannot be understated.”

The report comes out with AAA predicting that 43 million Americans will travel this Fourth of July weekend, the highest level of travel on record for the holiday and 5 million more travelers than over the Memorial Day weekend.

In New England, almost 2 million travelers will be driving to their destinations, up about 1.5 percent over last year.

Interstates, which are separated from other roads and rail lines and typically have a minimum of four lanes, paved shoulders and median barriers, are more than twice as safe as all other roadways.

Nationally, the TRIP report says, the fatality rate per 100 million vehicle miles of travel on interstates in 2014 was 0.54, compared to 1.26 on non-interstate routes.

In Connecticut, the non-interstate fatality rate was more than double the interstate fatality rate — 0.98 versus 0.41. TRIP estimates that the Interstate Highway System saved 5,359 lives nationwide in 2014, including 59 lives in Connecticut.

Founded in 1971, TRIP researches, evaluates and distributes data on transportation issues. It’s sponsored by insurance companies, equipment manufacturers, distributors and suppliers; businesses involved in highway and transit engineering and construction; labor unions; and organizations concerned with safe and efficient transportation.

b.hallenbeck@theday.com