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Traffic analysis flags Mystic St., Bartlett St. and Boston Water & Sewer driveway as chokepoints for Lower Broadway busway
Summary
MBTA traffic staff presented preliminary modeling showing the worst congestion at the Mystic Street/Encore driveway and Bartlett Street intersections and said mitigation (added southbound left‑turn lane at Bartlett, signal timing changes) could improve operations; Alternative 2’s single northbound lane north of Thorndike was judged unacceptable.
MBTA traffic staff told attendees that their initial screening identified several intersection movements that would require mitigation if a separated busway is built on Lower Broadway and Alford Street.
Gary, the project traffic analyst, said the analysis used existing roadway geometry and near‑term development projections to screen alternatives and identified the Mystic Street/Encore driveway (southbound) as the most problematic location during morning peak hours. “We’re seeing that queuing at that Encore driveway, Mystic St. intersection, the morning peak hour with that heavier southbound flow,” Gary said.
He added Bartlett Street shows significant delay in both morning and afternoon peak periods and that adding a southbound left‑turn lane onto Bartlett is a primary mitigation measure the team is evaluating. Gary explained that queue‑length metrics and signal timing coordination are central to preventing queuing from spilling back and creating corridor‑wide gridlock.
On the two design options, Gary said Alternative 2’s requirement to reduce general‑purpose northbound capacity (to one lane north of Thorndike) led to “unacceptable traffic operations” in his model runs; that finding is why MBTA staff do not plan to advance Alternative 2 as currently configured. For Alternative 1, staff said some intersections would see increased queuing but that additional intersection capacity and signal timing adjustments could convert those locations to acceptable operations.
Gary also said the modeling incorporated planned developments (Encore East of Broadway, Docklands Innovation District) and that the team ran evening/casino peak scenarios, though he emphasized the current analysis uses a conservative baseline that assumes no immediate mode shift from driving to transit or biking. “At this point we haven't assumed that there is any diversion. We've still kept all of the vehicles that are there today,” he said, and added the Silver Line alternatives study contains more detailed ridership/mode‑shift appendices.
MBTA staff said further analysis will explore targeted mitigations (signal timing, turning-lane geometry) and that design refinements—such as preserving northbound general‑purpose capacity near Sweetser Circle and keeping a southbound left turn at Bartlett—will be considered in a hybrid alternative. The team also said additional traffic modeling and coordination with local projects will continue as the design advances.
