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Concord Avenue, Blanchard Road, and Griswold Street Proposed Imp
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The Engineering Division has designed an improvement to the traffic signal operation at the intersection of Blanchard Road, Concord Avenue, and Griswold Street.  This is a proposal and we are asking for comments from the neighborhood and the general public before proceeding with the work.

 

Our goal is to improve efficiency, eliminating the long lines of traffic on Blanchard Road and Concord Road westbound that is common during rush hours.  Today, the two sides of Blanchard Road (northbound and southbound) run at separate times.  This results in long lines and wait times. We have analyzed the operation and can reduce these queues by running northbound and southbound Blanchard together.  We can accomplish this safely by adding new line striping within the intersection to allow space for and to organize left turns.  When complete, the intersection will be safer and less congested.

The proposed design is shown below.

 133

 

 

We are also proposing to add a traffic signal phase for Griswold Street.  As you know, there is no traffic signal indication for Griswold Street today.  Drivers currently exit Griswold when they can during the regular cycle.  At heavy traffic times of the day, or for users unfamiliar with the signal operation, this can be unsafe.  By adding a light for Griswold Street, we can eliminate confusion and improve the safety of the intersection.

 

With the proposed changes, the intersection will operate as shown in the sequence of drawings shown below.

The westbound direction goes first and the left arrow comes on, as it does today:

133 ph4

 

Then the arrow turns off and the eastbound direction starts:

 133 ph1

 

The northbound and southbound directions will run together.  We will create space for southbound left-turning cars to wait to turn left within the intersection.  Southbound drivers going straight will be able to flow by them.  (Few northbound drivers turn left, so we do not need a northbound left-turn lane.) 

133 ph2

 

 And finally, Griswold Street will get a green light – but only if cars are waiting.  Griswold will have a wire loop detector, or sensor, buried in the street, which will tell the traffic signal when a car is waiting for the light to turn.  If no car is waiting, the light will not turn green and Concord Avenue will get its turn again.

 

 

133 ph3

 We have heard in the past from residents in the area that making any improvements to the intersection of Concord Avenue at Griswold Street will attract cut-through traffic. We don’t believe this would happen. With the southbound Blanchard Road approach to the intersection much less congested after the improvements, commuters will get through the intersection faster by staying on Blanchard Road as opposed to cutting though the neighborhood and turning left on Griswold. 

 

Please submit any comments or questions to the Principal Traffic Engineer, Jeffrey R. Parenti, P.E. jparenti@cambridgema.gov          

 

 

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