Drivers Beware of New Traffic Patterns at Intersection on Common St.

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Will Brownsberger

State Sen. Will Brownsberger warns drivers to be aware of changes to in the traffic lights at an intersection near the Watertown-Belmont line due to work on Trapelo Road.

Brownsberger recently published this post on his website:

Change is hard and important change has happened at the intersection of Common Street and Trapelo Road.

It used to be that traffic with a green light on Common Street could turn left.  Only one direction of Common Street had the green at a time.

Now there are separate signals for left and straight. Both directions of Common Street go green for left turn at the same time now. And both directions go green for straight at the same time.

Don’t continue across Trapelo on Common except on the straight green. There has been serious confusion especially for traffic coming from Watertown — going straight on Common involves a slight left and many people have been making that slight left on the left arrow, which is intended only for the hard left onto Trapelo shown in green on the image above. This repetitive error is causing near collisions with traffic properly turning left from Common Street onto Trapelo from the Belmont Center side.

Everyone involved is very aware of the confusion and the risk involved.  The Belmont Town Engineer, the Belmont Police, Mass Highway and the consulting engineers are all working together to make the situation safer.


Here (via the Town Engineer) are their immediate plans coming out of a meeting this afternoon:

  • The sign board will be re-programmed to better explain the purpose of the two lanes
  • There will be no parking allowed on the right side of Common street from the gas station at 500 Common Street to the corner. This will make it visually clearer that there are two distinct lanes at the intersection.
  • Belmont DPW will paint an extension of the white lane delineation line on Common Street, from the end of the current white line to further up Common towards Belmont Street to help guide traffic to the proper lane
  • Belmont DPW will paint dashed white lines for the Left Turn Only lane so drivers will see exactly where they are supposed to go when they get the green arrow
  • Directional signs are due to arrive on Monday and will be mounted immediately on the mast arm next to the traffic signal heads
  • For the rush hour tonight (approx. 3-7) Mass DOT is paying for a police detail to work in the intersection to help motorists properly maneuver through the intersection

It is also recognized that an additional head directly adjacent to Common Street headed north may be needed to show red to cars likely to make the recurring error (going straight across Common on the left arrow from Watertown).

See this earlier post for more updates on the Belmont/Trapelo Road project.

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