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 with complaints from those who ride buses and carpools that now must pick their way through traffic just like the rest of us.

Meantime, 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 began, appropriately enough, on April Fool’s Day and involved shutting down key travel lanes. That 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.

The ensuing headaches 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 non-carpool commuters are usually forced to squeeze down into two lanes of travel.

It was no panacea, nor was it permanent. Lately highway officials are discussing whether to keep the lane open to general travel for the duration of the two-year Tobin Bridge work.

We say they should, even if it will ruffle advocates for carpools and public transit, who complain that opening the lane removes an important incentive that shakes people out of their one commuter, one car habits. Whether opening the lane slows down bus trips, as they suggest, will be tested by traffic counts that highway officials pledge to conduct before making a final decision, according to Statehouse reporter Christian Wade’s reporting.

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, although only marginally so. Meanwhile, clearing up the lane-drop for all other traffic allows commuters to pass through the I-93 narrows more quickly. Keeping that lane open while the Chelsea work is underway is 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, transportation officials 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, he 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 idling 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 people who can shift their schedules. The reality is that many who drive to and from work cannot be so flexible.

If the Highway Department can take steps to alleviate severe traffic congestion caused by the bridge work, it should do it.

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