East Hartford — Gov. Dannel P. Malloy announced Thursday that the state Department of Transportation has determined the proposed widening of Interstates 95 and 84 would produce $40 billion in economic benefits by 2040, about four times the estimated cost of the projects.

With I-84 traffic whizzing by behind him, the governor told reporters gathered outside a DOT maintenance facility here that his highways plan would generate more than 20,000 construction jobs and reverse decades of neglect.

“Quite frankly, Connecticut residents have been shortchanged for 40 years,” Malloy said.

Unveiled earlier this year, the Democratic governor’s 30-year, $100 billion transportation plan calls for improvements to highways and other infrastructure, and to rail and bus systems and bike trails. Republicans have criticized the plan as overly ambitious and too costly.

The widening of I-95 in southern Connecticut would involve adding a lane along much of the expanse in either direction, from Greenwich to North Stonington. The undertaking would produce $15.5 billion in new business sales, add $9 billion to Connecticut’s gross state product, generate $6.3 billion in new wages for workers, and support between 11,000 and 19,000 construction jobs over a 10-year ramp-up period, according to the DOT’s analysis.

Widening I-84 between Danbury and Waterbury would produce $4.4 billion in new business sales, add $2.6 billion to the gross state product, generate $1.8 billion in new wages and support 4,000 construction jobs.

“This is about long-term thinking, about delivering a down payment on our future,” Malloy said. “It’s not just about quality of life — our transportation system is directly tied to our state’s economic future and our ability to grow jobs. The DOT’s analysis demonstrates that by acting now, we will see dramatic benefits in the long term.”

Meanwhile, state Senate Minority Leader Len Fasano, a North Haven Republican, issued a statement critical of the DOT’s findings.

“The DOT analysis released today fails to talk about the massive tax hikes the governor will need to inflict on taxpayers to pay for his oversized and unrealistic $100 billion plan,” Fasano said. “It fails to talk about the potential job losses that would follow. It fails to talk about the burdens every single person in Connecticut will face as a result of a plan that counts on money our state simply doesn’t have and cannot afford.”

Fasano said only four places in the world have approved a $100 billion transportation initiative: the countries of Mexico and Colombia, the province of Toronto and the state of California — “all areas much larger than Connecticut.” He said Republicans would fund transportation improvements through appropriations of $1 billion a year for the next 30 years without the need to raise taxes.

State Transportation Commissioner James Redeker and state Department of Economic and Community Development Commissioner Catherine Smith, who joined Malloy at Thursday’s press conference, said the governor’s proposed improvements were key to easing the traffic congestion that threatens to choke off Connecticut’s economy.

“This will help companies twice, by creating jobs and by making existing workforces more productive because they won’t be stuck in traffic,” Smith said.

The DOT analysis found that widening I-95 would save travelers well over 14 million hours of delays by 2040. Widening I-84 would save more than 4.7 million hours of delays.

Interstate 95, built in the 1950s to carry 50,000 vehicles a day, now handles three times that in the New Haven area and about 100,000 vehicles a day between the Connecticut and Thames rivers in southeastern Connecticut. An estimated 80,000-plus vehicles travel I-84 daily.

The governor’s transportation plan also calls for rehabilitating the Gold Star Memorial Bridge, which spans the Thames between New London and Groton.

Malloy said funding for design work related to I-84 improvements in Danbury has been approved and that preliminary work is underway.

b.hallenbeck@theday.com

Twitter: @bjhallenbeck