Trapelo/Common Intersection (68 Responses)

As many of you have urged, engineers from MassDOT and the Town have reconfigured the intersection to something resembling its original configuration — cars on Common Street north bound now have green for straight and left simultaneously and then the south bound cars get green and left simultaneously — as the intersection worked before the changes. The description below and the drawing above are no longer accurate. Thanks to MassDOT and the Town for responding aggressively to the problems. Keep the feedback coming.

However, as of December 10, the project engineers still do want to retry the configuration described below which failed. The failed configuration makes good sense in terms of safety and throughput, but only if motorists can understand it. Whether signage, striping and possibly additional signals will accomplish that is an open question for consideration over coming months.

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.

This whole thread has been brought to the attention of the consulting engineers (initially on 9-21) and I am hopeful that they are considering all the suggestions and feedback offered below as they review the situation.

Please note, this thread is not open for comment at this time.


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    Will Brownsberger
    State Senator
    2d Suffolk and Middlesex District