Leaving open the carpool lane on Interstate 93 south to all commuters is a straightforward remedy to ease traffic on an artery burdened because of work on the nearby Tobin Bridge. But like so many things, especially ones involving traffic and highways in Massachusetts, doing so has become contentious amid complaints from those who ride buses and carpools that now must pick their way through traffic just like the rest of us.

Meanwhile, another sensible step that would leave open breakdown lanes on the interstate to commuter travel, again with an eye toward easing the morning and afternoon crowds, has been set aside by the state Highway Department for what appear to be bureaucratic reasons.

All of which suggests that, as necessary as the two-year project to repair the Tobin Bridge may be, contingency plans for its residual effects are woefully inadequate.

A $47 million project on the Tobin Bridge actually has been underway for a year. The traffic crunch really started with its companion, $169 million project on the Chelsea Viaduct — the long, curving, elevated portion of Route 1 just north of the bridge. The rehab of that structure started, appropriately enough, on April Fools’ Day and involved shutting down key travel lanes. And it doesn’t just affect North Shore commuters. It’s the vehicular equivalent of an artery blockage, raising the pressure on highways and thoroughfares throughout the region, particularly I-93.

The ensuing headache prompted MassHighway officials to look for relief by way of the 2.6-mile, high-occupancy vehicle lane, normally reserved at rush hour for carpools and buses, on I-93 south between Medford and the Zakim Bridge. Opening the carpool lane to everyone back in May loosened the burden that extra commuters put on interstate traffic in an area where noncarpool commuters are usually forced to squeeze down into two lanes of travel. With the lane open, all cars may travel through that spot using all three lanes.

It was no panacea, nor was it permanent. But lately, state highway officials have been discussing exactly what temporary means, and specifically whether to keep the lane open to general travel for the duration of the two-year Tobin Bridge work.

The idea ruffles advocates for carpools and public transit, who say opening the carpool lane means shutting down an important incentive to shake people out of their one-commuter, one-car habit. “It seems to fly in the face of what we’re trying to do — ease congestion,” Monica Tibbits-Nutt, a member of the MassDOT board, said during a meeting early last week. “This is causing significant delays for our bus services.”

Whether that’s true will be tested by traffic counts that highway officials pledge to conduct before making a final decision, according to Statehouse reporter Christian Wade’s account of the MassDOT meeting. We’ll wait to see what the numbers say, but the presumed result is that a bus ride involving the carpool lane is indeed slower now that all traffic is allowed to travel there, although not greatly slower. Meanwhile, clearing up the lane drop for all other traffic allows commuters to pass through the I-93 narrows more quickly.

Hopefully, when the counting’s all done, MassDOT will see the logic of keeping the lane open while the Chelsea work is underway. It’s an easy step serving the greater purpose of ensuring the safe, efficient use of one of Greater Boston’s busiest highways.

While they’re at it, the MassDOT should revisit a decision not to extend hours of breakdown lane travel on the interstate — an idea advanced by Sen. Barry Finegold, D-Andover. The breakdown lanes now work as regular travel lanes for four hours in the morning, then again in the afternoon. Finegold’s idea was to widen that window by an hour on either side. The idea was rejected, Finegold has said, due to MassDOT’s rationale that to expand hours of breakdown lane travel in one area would require doing so everywhere in Greater Boston. Think on that the next time you’re stuck staring at the brake lights ahead of you on I-93.

State transit officials’ advice to North of Boston commuters affected by the Tobin Bridge repairs has been to travel earlier or later, or take the T. Those are great tips for those who can make them work. The reality is that many who drive to and from work do so because of the demands of schedules and location. If MassDOT can take steps to alleviate severe traffic congestion caused by the bridge work, it should do it.

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