Survey Says! Drivers Going Slower by Grove Street Traffic Improvements

Drivers are now driving slower on Grove Street in West Roxbury due to speed monitor displays and speed limit postings, according to a recent Boston Transportation Department study.

The Boston Transportation Department (BTD) released the results of a before and after study completed before and after the improvements on Grove Street. Residential complaints about speeding in the heavily-populated residential street led to the study. Residents approached BTD about drivers using the street as a cut-through between Washington Street in West Roxbury and Dedham. 

BTD Commissioner Thomas Tinlin and staff met on site with Grove Street residents in March 2012 and witnessed the speeding issue first-hand. That same month BTD conducted a before study using traffic data, such as speed, volume and vehicle classification. The study showed 83+% of drivers were exceeding the posted speed limit of 30 mph, according to a BTD press release.  Data showed the 85th percentile speeds were 40 mph in the northbound direction and 39 mph in the southbound direction (the 85th percentile speed refers to the speed at which 85% of the population measured did not exceed).

A traffic improvement plan developed consisted of the following enhancements:

• Installation of an edge line on Grove Street - an edge line is a 4-inch white pavement marking that defines the right edge of the travel lane. When an edge line is present it can narrow the travel lane width, and drivers tend to decrease speeds when travel lane widths are reduced.
• New crosswalks were installed and pedestrian warning signs were posted at the intersections of Grove and Birchwood streets, and Grove and Stimson streets.
• Speed monitoring displays were installed at #297 and #351 Grove St. The radar-activated signs let approaching drivers know how fast they are going.  The displays hang below a fixed 30 mph sign to let drivers see their speed in relation to the posted speed limit.   

The traffic improvement plan was implemented in the fall of 2012, and conducted its after study on May 30, 2013.  Results of the after study are listed below.

• The percentage of drivers exceeding the posted speed limit of 30 mph was reduced from 83.6% in the before study to 36.5% in the after study.
• The percentage of drivers exceeding 35 mph was reduced from 37.3% in the before study to just 5.4% in the after study.
• The 85th percentile speeds were reduced by 6 to 8 mph in each direction.
• As a result of the analysis, it was determined with a 99% confidence level that the difference in the before and after speeds is significant and due to the improvements.
• Overall, traffic volumes increased by approximately 6%, however, this may be due to seasonal traffic fluctuations as traffic volumes fluctuate by month and season, and according to available data, traffic volumes have been proven to be 6% lower in March than in May in this area.
• The percentage of large trucks was also reduced from 10.9% to 6.4%.

Questions or comments about the Grove Street traffic improvements should be forwarded to the Boston Transportation Department Engineering Division at BTD@cityofboston.gov