Susan Scribner was pumping gas just off Interstate 93 and getting ready to rejoin the sea of red brake lights flowing north. She had already been inching along the highway for 30 minutes.
"Look at it - traffic is worse than ever," said Scribner, an accountant who, since 1994, has commuted between her home in North Reading and Cambridge. "It's worse since the Big Dig - totally worse."
A Globe analysis of state highway data documents what many motorists have come to realize since the new Central Artery tunnels were completed: While the Big Dig achieved its goal of freeing up highway traffic downtown, the bottlenecks were only pushed outward, as more drivers jockey for the limited space on the major commuting routes.
Ultimately, many motorists going to and from the suburbs at peak rush hours are spending more time stuck in traffic, not less. The phenomenon is a result of a surge in drivers crowding onto highways - an ironic byproduct of the Big Dig's success in clearing away downtown traffic jams.
The worst increase has been along I-93 northbound during the evening commute. In 1994, before the tunnels were dug, it took, on average, 12 minutes at peak evening rush hour to go the 11 miles from the Zakim Bridge to the Route 128 interchange in Woburn.
Now it takes 25 minutes, double the time.
Traffic is also three minutes slower during the evening rush on the Southeast Expressway, heading south out of the Thomas P. O'Neill Jr. Tunnel, and five minutes longer going west on the Massachusetts Turnpike. In the mornings, delays have grown by almost three minutes from the north, by more than five minutes from the south, and by about four and a half minutes from the west.
The upshot is that Massachusetts, for the $15 billion invested by the state and federal taxpayers, got a gleaming new highway system that has made zipping beneath Boston and Boston Harbor much easier. It increased overall mobility by allowing more people to travel at peak times. But most travelers who use the tunnels are still spending time in traffic jams - just not in the heart of the city, where bumper-to-bumper was a way of life on the old elevated artery.
The Globe developed its findings by analyzing state drive-time data collected in 1994 and 2006 - before and after the Big Dig tunnels and connector roads opened. The data is regularly collected by state employees who drive the highways and time their trips and is then used by the state Executive Office of Transportation to help set policy.
State traffic specialists say the data is the most up-to-date and best available for measuring the impact of the Big Dig. The data was collected before a ceiling collapse in the connector tunnel in July 2006 killed a motorist and prompted months-long closings of some portions of the Big Dig tunnels.
The Globe findings provide a fuller picture of the traffic situation than a state-commissioned study done two years ago, in which the Big Dig was credited with helping to save at least $167 million a year by increasing economic productivity and decreasing motor vehicle operating costs. That study did not look at highways outside the Big Dig construction area and did not take into account new congestion elsewhere.
The findings also call into question the promises made when ground was broken in 1992. At the time, state officials said in a promotional mass mailing to the public that, when it was all done, "people will find the commute to their jobs faster and easier than ever."
Frederick P. Salvucci, the former state transportation secretary who pushed the project in the 1970s and 1980s, now says that he and others anticipated that there would be bigger delays outside the city, unless transit options expanded significantly. He says he made the point at public meetings.
"This isn't a surprise - we saw this coming," he said of the Globe findings. "We knew there would be more bottlenecks within Route 128."
"I still believe it was the right thing to do," Salvucci said of the Big Dig. "We fixed the worst bottleneck."
Alan LeBovidge, executive director of the Massachusetts Turnpike Authority, which operates the Big Dig, said he agrees that there is an increase in congestion on highways outside the Big Dig, which he said reflects the region's economic vitality, but disputed any connection between those delays and the Big Dig.
"It's just that the highway system is overstressed," he said. "There is more congestion, but it has nothing to do with the Big Dig. We just have a lot of people using the highways."
The Big Dig removed the chronic clogs in Boston, made access to Logan Airport a snap, spurred economic development along the harbor waterfront, and made the Rose Kennedy Greenway possible, he said.
"This was a worthy investment," he said. "I wish it could have been done for half the cost, but in the end the project really helped the region."
The cause of the delays on highways that lead into the Big Dig is, perhaps not surprising: more cars and trucks. On I-93 north of the city, for example, 202,000 motor vehicles drive past Roosevelt Circle in Medford, 38,000 more than in 1987, a 23 percent increase, according to state data.
Similarly, there are about 250,000 motor vehicles daily on the Southeast Expressway near Neponset in Dorchester, a 22 percent increase. It is the most heavily traveled section of highway in the state. On the Massachusetts Turnpike, daily volume is about 138,000 vehicles east of the Allston-Brighton tollbooths, an increase of 29,000, or more about 27 percent.
Two factors contribute to the surge. Overall, people are driving more, increases in gasoline prices notwithstanding. Also, drivers who once avoided the I-93 corridor, choosing instead to drive around Boston on Route 128, for example, now are willing to plunge ahead into the city, said Jeff Larson, general manager of SmartRoutes Systems Inc., who has tracked traffic patterns in Boston for 18 years.
"The Big Dig was not some magic wand that was going to make traffic congestion all over metropolitan Boston disappear - that was never the claim," said Larson, who says the overall traffic picture is improved.
"What has happened is the bottlenecks have moved, to just outside the Big Dig," Larson said. "It's sort of a case of 'If you build it, they will come.' "
Carrie Russell, staff attorney for the Conservation Law Foundation, said the Globe analysis of commuter times shows "we can't pave our way out of congestion."
"Adding more traffic lanes only attracts more people to highways and the roads leading to those highways," she said. "Suddenly, it's attractive to drive through the downtown tunnels, because they are relatively clear of traffic, and that's causing a pile up of traffic on the thresholds to the tunnel."
When the Big Dig was proposed in the 1980s, the Conservation Law Foundation challenged it on environmental grounds and wrung out a settlement that called for the state to expand public transit, including the Greenbush commuter rail and the yet to be completed expansion of the MBTA's Green Line into Medford.
Russell said to get people out of automobiles, and therefore to reduce emissions of climate-changing greenhouse gases, public transit must be expanded.
Salvucci also remains a firm advocate of further expansion of the MBTA and a lowering of fares to attract more transit riders.
"You can not expand highways enough to end congestion," he said.
The numbers clearly show that commuters are no longer bedeviled by the elevated Central Artery, the 1.7-mile stretch between the Charles River and South Station that was once considered the worst bottleneck in the nation's 41,000-mile interstate highway system. Traversing the central city underground can usually be done now in about 3 minutes, compared to 15 minutes at its worst in 1994, according to the data. What's more, congestion on the Central Artery once slowed traffic to a crawl for up to14 hours daily. Today, the tunnels are almost always passable.
On Route 1, the effects have been mixed. In the morning, it actually takes five minutes less to get into the city (the only case that shows a shorter commute after the Big Dig, perhaps because more motorists are using the Ted Williams Tunnel rather than the Tobin Bridge). Going home, however, takes 10 minutes longer.
During an informal survey of a dozen commuters arriving at a downtown Boston parking garage one morning last week, a consensus seemed to emerge that while the downtown commute is better, the "prong" roads are problematic.
"It's as long as it's ever been, if not longer," said Peter Ferrelli of Winchester, who works downtown in investor services, of his commute on I-93.
Afternoon commutes are almost always miserable, he said, while he has detected some improvements in the mornings.
"I just don't know if it has been worth billions," he said.
Sean Murphy can be reached at email@example.com.