CMA 2017 #168 · Agenda item attachment · Jun 12 2017

City of Cambridge 1 Traffic, Parking, and Transportation City of Cambridge – Traffic, Parking, and Transportation Department Intersection Safety Review Brattle Street, Sparks Street, and Craigie Street Background This study is in response to Council Order #1 from the November 7th, 2016 City Council Meeting (Awaiting Report 16-89), requesting a safety review of the vehicle, pedestrian, and bicycle facilities at the intersection of Brattle Street, Sparks Street, and Craigie Street, as well as recommendations for short and long-term improvements. Existing Conditions Figure 1: Intersection of Brattle St, Craigie St, & Sparks St, Google Maps The junction of Brattle Street, Sparks Street, and Craigie Street (Figure 1) is a five-legged intersection controlled by STOP signs on the Sparks Street southbound (SB) and Craigie Street southwest-bound (SWB) approaches, respectively, and free-flow along Brattle Street in the eastbound (EB) and westbound (WB) directions. Supplementary to the STOP control, post-top flashing beacons flash red for the Sparks Street and Craigie Street approaches, and flash yellow for Brattle Street WB approach (the Brattle Street EB approach does not have a flasher). The northern leg of Sparks Street is a single-lane one-way approach into the intersection while the southern leg is one-way away from the intersection. Craigie Street is a two-way street and has its approach and departure lanes (both on the north side of Brattle Street) physically separated by approximately 60’ from each other by a triangular traffic island, which contains landscaping and large tree. Brattle Street, also a two-way, is one lane in both directions except within the intersection, where the road widens to provide a dedicated EB left turn lane onto Craigie Street. The intersection’s geometry is such that Sparks Street and Craigie Street, heading toward Brattle

City of Cambridge 2 Traffic, Parking, and Transportation Street, meet at a 90-degree angle just north of Brattle Street. To travel northeast-bound (NEB) along Craigie Street, away from Brattle Street, vehicles must enter using the slip lane on the northeast side of the intersection. This slip lane can be accessed from Brattle Street by a WB right turn or an EB left turn from the left turn lane. There are crosswalks across every leg of the intersection; the crosswalk across the west side Brattle is supplemented with a 30’ long by 4’ wide raised pedestrian refuge island installed in recent years as part of a traffic calming project along Brattle Street. Bike lanes (5’ wide) are provided on every leg of the intersection except for the Craigie Street approach and departure lanes. Parking is prohibited on Brattle Street on the EB and WB approaches within 60’ and 170’ (respectively) from the closest intersecting street. Craigie Street parking is prohibited within 70’ for the NEB lane and 100’ for the SWB lane, while Sparks Street has parking prohibited within 50’ of the intersection on the north side and within 25’ of the intersection on the south side. Crash Data Analysis For the purposes of this evaluation, we analyzed all the crash reports documented by the Cambridge Police Department for the three years from January 2014 to December 2016. There was a total of 14 crashes recorded during this time period; four involved bicyclists and none involved pedestrians. Of the 14 crashes, 11 (79%) were angle, two were rear-end, and one was a head-on crash. No recorded crash involved a motorist traveling toward Brattle Street from the Craigie Street approach. In the morning, because of the directionality of Brattle Street, the sun glare can be blinding for motorists approaching from Sparks Street and Craigie Street searching for gaps in Brattle Street traffic. One crash involving a cyclist explicitly mentions this issue and three crashes (20% of the total number and 50% of the SB vs WB collisions) occurred during the time window when the sun is most distracting. Seven crashes (50%) were between motorists heading SB through the intersection and vehicles (or cyclists) heading EB on Brattle Street. Four crashes (29%) were between motorists heading SB and vehicles (or cyclists) travelling WB, such that approximately 80% of the total crashes occurred between a vehicle heading south on Sparks Street and vehicles (or cyclists) heading EB or WB on Brattle Street. These crash data indicate a significant pattern of angle crashes for through vehicles on Sparks Street. Angle crash patterns such as these are correctable with intersection control improvements including all- way STOP control, a modern roundabout, or a traffic signal. Recommendations All-way STOP control at this location would not be feasible based on the high peak hour traffic volumes on Brattle Street (between 950 and 1350 vehicles per hour during the peak periods). We evaluated the possibility of a standard or skewed modern roundabout treatment for this intersection. A modern roundabout would reduce speeds on Brattle Street in the area of the intersection while improving safety for all users. However, the right-of-way required to fit the roundabout, separated bike lanes, and sidewalks would significantly impact at least one adjacent private property, as well as require substantial changes to curblines and sidewalks, as well as the removal of the mature tree within the traffic island. Based on these significant impact, we have eliminated a roundabout from consideration.

City of Cambridge 3 Traffic, Parking, and Transportation Preliminary analysis of the traffic volumes indicates that this intersection meets the warrants laid out in the Manual on Uniform Traffic Control Devices (MUTCD) for the installation of a traffic signal based on the four-hour and peak-hour signal warrants. Based on this analysis, adding traffic signal control at this location appears to be the most reasonable course of action to address the safety and operational issues identified during this review. Our next step would be to review this option in greater detail, particularly in terms of how this new signal would operate in the context of overall traffic patterns in this area, and then to review these analyses and conclusions with the local community. Next Steps To move this improvement forward, we will be undertaking the following next steps:  We will identify capital funding to support design and construction of the new signal.  We will begin more detailed design of the signal improvements, including identifying any physical/geometric changes that are needed.  We will hold a community meeting about improvements at this intersection before the end of the year. In addition, installation of this signal will need to take place in coordination with any improvements (potentially including installation of a traffic signal) at the intersection of Sparks Street and Mount Auburn Street, which would take place as part of the Willard Street design project that the Department of Public Works recently initiated.