Traffic analysis projects lane reduction will divert some peak-period trips; town to collect baseline counts before pilot

Consultants told the Envision Needham Center Project Working Group on March 3 that a road-diet pilot that reduces multi-lane approaches to one travel lane per direction would lower capacity and likely divert some peak-period vehicles to nearby streets; the team is planning baseline counts and further modeling before a pilot.

The analysis is a three-step approach: estimate how many peak-hour trips would be diverted, identify likely alternate routes, and quantify diverted volumes at key intersections to determine where monitoring and mitigation are needed.

Presenters and assumptions

Jim Fitzgerald, a project presenter, described how the team estimated diverted trips out to a 10-year horizon using background growth rates and known or planned developments. Steve Cicari provided peak-hour definitions, saying the morning peak hour is 07:45–08:45 and the afternoon peak is 17:00–18:00. The team emphasized several base assumptions: approaches into the center would be reduced to one lane per direction, pedestrian signal phasing at the two primary intersections would be exclusive, and signal timings would be optimized for the new lane configuration.

Key findings and data points

- Trip character: Lucy Gibson, one of the consultants, said the Replica data analysis shows a large share of morning peak trips passing through Needham are long commutes; "a huge percentage of these trips are longer than 16 miles, 60%." She also reported that about 55% of AM peak trips were work-related.

- Diversion examples: Presenters gave examples of projected diverted volumes in the peak hour. For one approach into the center, the model estimated about 32 motorists in one AM peak hour would seek an alternate route from Dedham Avenue. In a worst-case scenario that assumes all diverted traffic remains on local streets, routes such as South Street, High Rock Street and Webster Street would absorb concentrated increases; other modeling scenarios distributed traffic more widely or assumed longer trips would use regional highways.

- Two scenarios: The team presented a "worst-case" scenario that assumed diverted trips remain on nearby local streets and a more realistic scenario that incorporated mode shifts, short trips becoming walk/bike trips, and long trips shifting to regional highways.

What the working group requested

Working-group members asked for context and baselines. Several members requested a "future no-build" comparison (projected traffic in 10 years without the road diet) and current baseline counts on side streets so residents can see how much additional traffic a diversion would represent. The consultants agreed to provide the future no-build baseline and recommended collecting counts at about 10 intersections before the pilot and again during the pilot to compare model predictions with observed changes.

Next steps and public outreach

Staff said they will refine the model, identify a prioritized list of intersections for baseline counts and coordinate public outreach ahead of the pilot. They described planned mitigation planning—such as temporary or longer-term treatments, signal adjustments or traffic calming—if data show unacceptable impacts at particular intersections. Project staff also recommended public notification before the pilot (changeable message signs, flyers, digital notices) and emphasized that the pilot is intended to produce real-world data to compare against model projections.

Ending

Consultants said the pilot will provide a chance to observe actual diverted volumes and adjust designs before finalizing permanent changes; working-group members urged clear context for model assumptions and timely publication of baseline counts so residents can compare before-and-during pilot conditions.