Transit Matters Identified Slowest Boston Bus Routes
A 2025 analysis revealed the SL4 bus route as the city's slowest, highlighting persistent transit delays.
Updated on Sept. 21, 2026 in Transportation
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In October 2025, Transit Matters identified the SL4 bus route between South Station and Nubian Station as the slowest in the city, with an average speed of 6.09 mph. This report highlights how the ten slowest routes in Boston have continued to struggle with congestion and scheduling efficiency.
Why it matters
The analysis underscores a growing transportation equity gap, as seven of the ten slowest bus routes serve Roxbury, where 39% of residents lack access to a personal vehicle. These delays directly impact the daily mobility and economic access of communities that rely most heavily on the MBTA.
The SL4 route averaged 6.09 mph in October 2025, while the 32 bus exhibited a 17.1 percent bunching rate. These figures contribute to a 13.9 percent average bunching rate across the ten slowest routes citywide.
The players
Transit Matters
This is a transportation advocacy organization that monitors MBTA performance and promotes improved transit infrastructure in the Boston area.
MBTA
The Massachusetts Bay Transportation Authority is the primary public agency responsible for operating public transit services throughout the Greater Boston area.
The details
The report identified routes based on data from October 2025, tracking how many buses failed to maintain even spacing while traversing neighborhoods like Dorchester, Hyde Park, and Jamaica Plain. To address these issues, the city has proposed installing bus-mounted enforcement cameras to fine vehicles occupying restricted transit lanes.
Timeline
In 2023, the top 10 slowest bus routes recorded an average speed of 6.83 mph.
Data for the Transit Matters report was collected throughout October 2025.
The findings were formally released in a report published in September 2026.
Market Landscape
This analysis reflects the ongoing struggle of urban transit systems to maintain reliable service levels in increasingly congested corridors. The findings follow the service reliability goals established by the MBTA Better Bus Project while highlighting the gap between current transit capacity and infrastructure demand.
Commuters relying on the SL4 and other slow-moving routes may continue to face significant travel delays until planned bus lane expansions are completed. Residents should anticipate potential changes to street enforcement as the city begins using cameras to fine vehicles blocking bus lanes.
The takeaway
The concentration of the slowest bus routes in Roxbury demonstrates that transit congestion is not just a logistical inconvenience, but a significant barrier to economic equity. Passengers can mitigate the impact of unpredictable scheduling by checking real-time transit apps before departing for their commute.
Further reading
For more on local infrastructure developments, see the Transportation section.
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Does your local government prioritize improving bus service for neighborhoods that rely on it most?
