After months of number-crunching, analytics, traffic simulations, and algorithms, Massachusetts Department of Transportation experts believe they have found a way to safely divert 30,000 motorists when the Callahan Tunnel closes Friday night for a three-month overhaul.
The plan includes major rerouting — detours through the Ted Williams Tunnel, over the Tobin Bridge, and along Route 1A — and smaller, more circumscribed ideas that they hope will, collectively, scatter the ill-effects of increased traffic.
Think retimed intersections and beefed-up bus and train schedules, along with the opening of little-known bypass roads and high-occupancy vehicle lanes. Electronic signs will provide real-time detour directions.
"We are confident we can handle any additional traffic," highway administrator Frank DePaola said Monday at the MassDOT Highway Operations Center in South Boston. "After the first few days of upset, things should calm down."
Even with DePaola's optimism, the prospect of redirecting the Callahan Tunnel's traffic to other arteries is a daunting task in a region where the transportation system already seems to run at full capacity.
Highway officials have identified three primary alternative ways for drivers to reach East Boston during the closure.
Drivers coming from the south should use the Ted Williams Tunnel. Those from the west will be urged to go over the Tobin Bridge. And motorists coming from the north will be diverted to take Route 16 East to Route 1A South.
Additionally, several industrial bypass roads and high-
occupancy vehicle lanes will be open to all traffic in an attempt to better funnel cars toward the airport.
"We feel with the three detour routes, people will learn the routes that have the least congestion and adjust to those," DePaola said at a press conference. "It will spread the load out over the multiple detour routes. We should be able to handle it."
There are other, less well-known detours that DePaola hopes will provide a release valve after the Callahan, which funnels traffic one way from the North End to East Boston and Logan International Airport, closes at 11 p.m. Friday.
Case in point: The high-
occupancy vehicle lane that leads from Kneeland Street at South Station straight into the entrance of the Ted Williams Tunnel. The roadway, currently restricted to cars with two or more passengers, will be opened to all drivers.
Currently, the road carries about 200 cars per hour during peak times, but has the capacity to accommodate 1,500 to 1,800 cars per hour.
"Most people get off before they ever see it," DePaola said.
In addition, transportation officials are promoting the appeal of other shortcuts. The South Boston bypass road and the Martin A. Coughlin Bypass Road in East Boston, industrial haul roads, will be opened to the public.
MassDOT's electric message boards that tower over I-93 — signs that currently warn drivers about the imminent tunnel closure — will soon begin providing real-time messages to drivers about the best route to take to East Boston, depending on traffic at the moment.
Officials are suggesting that commuters take public transportation to reach the airport, though they acknowledged that there is little they can do to increase the capacity of the transit system. Already, every operable Silver Line bus runs during rush hour; the MBTA plans to add an extra bus to the rotation during nonpeak hours.
"That will be full capacity almost the entire day," DePaola said. Additionally, the T will add a train to the Blue Line during evening hours and will be extending hours at Bowdoin Station, which currently closes at 6:30 p.m. weekdays. During the Callahan Tunnel project, the station will stay open until 12:30 a.m.
Although the complete tunnel closure is expected to end March 12, with overnight closures to continue for months afterward, there are financial incentives and penalties in place that will give the contractor the impetus to finish early. The contractor will earn or lose $71,000 each day the project goes under or over schedule.
The tunnel, which opened in 1961, will undergo a major construction overhaul to fix problems in the deck and paneling that arose after a half-century of wear and tear. Concerns about those problems escalated last December, when one of the 100-pound wall panels clattered onto the roadway, prompting MassDOT officials to remove the hundreds of remaining panels.
"It's about done with its anticipated life cycle," DePaola said.
Although traffic engineers originally had considered partially closing the tunnel to allow some traffic during construction, they decided that strategy would still result in significant delays for drivers that would extend over an 18-month period.
DePaola said the transportation agency will make adjustments along the way. For the first several weeks of the closure, traffic engineers will meet daily to discuss solutions to problems as they arise.
They chose to start the project over the holidays in part because while many people travel during the holidays, traffic is lower between Christmas and New Year's Day than during a regular work week. DePaola said MassDOT will have an opportunity to fix problems before any full-blown gridlock hits.
Martine Powers can be reached at firstname.lastname@example.org. Follow her on Twitter @martinepowers.