Updated 9/18/2017

Q: What’s happening in Union Square?

A: On July 29, 2017, Prospect Street and Webster Avenue were converted to accommodate two-way traffic between Prospect Street/Webster Avenue and Somerville Avenue. Newton Street has been modified to restrict through vehicle traffic between Webster Avenue and Prospect Street. Click on the Traffic Pattern Change tab above for more information, including a diagram of the changes.

This work has included several phases: changing and/or removing existing signals, repaving portions of streets in and around Union Square, and repainting lane markings.

There are other projects within Union Square that are also in their early phases. For details on those projects, please refer to the following pages:

Q: What work is left to be done?

A: Contractors finished installing a flashing pedestrian beacon at the new mid-block crosswalk on Somerville Avenue between Prospect and Webster on Wednesday, August 30th. Blinking signage will be installed at the corner of Webster Avenue and Newton Street to reinforce the message that access to Newton Street is intended for abutters only. Reflective posts will be installed at numerous locations to help delineate new crosswalks and new bicycle facilities; tentative scheduling is for this work to take place the week of September 11th.



Small-scale work on sidewalks will occur throughout September to switch electric power feeds from old traffic signal control cabinets to newly installed cabinets. Once the power feeds are switched, the old cabinets will be removed.

The City is constantly monitoring traffic conditions and continues to make small adjustments to signal phasing and timing to help improve safety and operations at the three intersections affected by the traffic pattern change. Small changes to timing plans were made during the week of August 21st. Traffic counts will be performed in September to help inform additional tweaks to the signal timing plans.

Q: This project is supposed to help improve traffic in and around Union Square. How, and when, will that happen?

A: Switching Prospect Street and Webster Avenue to two-way adds mobility options for motorists and bicyclists. The City conducted multiple traffic studies to inform this proposal. An initial planning study for the two-way concept was conducted in 2007-2008, and the advanced traffic engineering was performed in 2014. New traffic data collection occurred in 2016 prior to the start of construction to validate the traffic models and calibrate them for current conditions.

The City’s traffic studies found that in the heart of Union Square, hundreds of vehicles must use Prospect Street and Somerville Avenue to access Bow Street to continue north and west of Union Square; enabling two-way traffic on Webster Street allows motorists the option of avoiding Somerville Avenue altogether. Similarly, Somerville Avenue westbound traffic can use Prospect Street, rather than Webster Avenue, to go south toward Cambridge. We have estimated that 50%-60% of westbound traffic on Somerville Avenue between Prospect Street and Webster Avenue may be able to avoid this segment in the future, resulting in less congestion and delay for motorists.

Two-way traffic is also calmer traffic, resulting in safer vehicle speeds, which helps reduce the number and severity of crashes.

Finally, converting Prospect Street and Webster Avenue to two-way traffic will help facilitate traffic detours during the Somerville Avenue Sewer Separation project, and the GLX.

Q: Somerville Avenue is really backed up through Union Square. What’s being done about that?

A: Since the traffic change took effect, we have been closely monitoring traffic in this area, across several departments (Traffic & Parking, Police, Transportation & Infrastructure). Understanding and utilizing the new pattern will take some time for motorists and bicyclists to become accustomed to, and we will continue to deploy resources to try to quickly assist in these changes. Police details have been stationed at major intersections to try to alleviate confusion and congestion, and are scheduled for the week of September 18th. Their work includes enforcement of “Do Not Block the Box” behavior at the Somerville Avenue / Washington Street / Webster Avenue intersection.

Several changes to the traffic signal timings have already been made to promote safety and mobility goals, and more changes are anticipated during the weeks of 9/18 and 9/25.



In terms of the current conditions, the City has directed its contractors to implement another signal timing plan change that addresses two key issues:

Evaluate the concurrent pedestrian phases of the signal cycle and consider reverting to exclusive pedestrian phase (i.e. all vehicle approaches get a red signal while all pedestrian approaches go). This is the primary safety concern we have heard from stakeholders since Labor Day. Add green time to the eastbound Somerville Avenue approach at Prospect Street to help clear the backups that have been extending back to Webster and causing “Block the Box” violations at Webster & Washington. This is the primary congestion/mobility concern we’ve been hearing over the past two weeks.

Looking forward, the City is scheduled to be collecting formal traffic counts the week of 9/25 and the week of 10/2. These new data points will help us continue to evaluate what changes are needed through the fall. The counts will be repeated in the spring, since peer cities that have made these types of traffic pattern change tell us that 6-12 months are often needed for the learning curve and transition process. Traffic signal operations will be calibrated regularly as new data arrive.