Tool Design presents A2R2 right‑sizing study, highlights opportunities for road diets, transit lanes and roundabouts

The Ann Arbor Transportation Commission on May 20 heard a detailed methodology update on the Ann Arbor Roadway Right‑Sizing (A2R2) study, which evaluates possible reconfigurations for 10 city multi‑lane corridors to cut speeds, improve safety and make room for transit and bicycle infrastructure.

Lucy Gibson, project manager for Tool Design, told the commission the study examined 30 subsegments—about 20 miles total—and used daily and hourly traffic counts to compare existing volumes with typical capacities for signalized five‑lane, four‑lane and three‑lane configurations. "The project purpose was is to look at 10 of the city's multi‑lane corridors to consider road reconfigurations that can reduce speeds and adopt target speeds, better organize traffic, address systemic safety issues for all road users, and incorporate the future transit and bicycle infrastructure," Gibson said.

Gibson said most segments fall in a moderate volume range—roughly 15,000–25,000 vehicles per day—making many good candidates for reconfiguration. The team grouped the study area into three buckets: opportunity corridors (where a three‑lane conversion would be within capacity, about 12 miles), potential corridors (some hours exceed three‑lane capacity, about 6 miles) and challenge corridors (several hours over three‑lane capacity, about 2 miles). Plymouth Road near the Route 23 interchange and State Street near I‑94 showed the highest observed volumes.

A central technical finding presented was the relative capacity of intersection treatments. Gibson showed typical hourly capacities used for screening: a three‑lane signalized intersection capacity in the team's example is about 840 vehicles per peak hour while a single‑lane roundabout can handle roughly 1,250 vehicles per peak hour, allowing some segments that exceed three‑lane signal capacity to be feasible with roundabout treatments. "If the same number of people are driving, but in a roundabout, it would easily handle the peak hour traffic," she said.

Commissioners asked how the team will weigh roundabouts against pedestrian and bicycle safety, especially near schools or high‑activity places. Commissioners noted that single‑lane roundabouts generally perform better for yielding and speed control than multi‑lane roundabouts and that pedestrian crossings, raised crosswalks and rapid‑flashing beacons are among design tools to improve safety. Gibson said the study will incorporate the city's Vision Zero and land‑use plans and prioritize lower target speeds—often around 25 mph—where corridors are planned to become more walkable and transit‑oriented.

Design approaches under consideration include quick‑build or "paint‑and‑post" solutions for near‑term changes, and longer‑term sections that would be addressed through reconstruction or redevelopment. The team also plans concept drawings for priority locations—especially intersections, where safety gains are typically greatest—and a fall public open house focused on concept designs.

Commission members asked for segment‑level graphics and the technical appendices; staff agreed to post the segment analysis and charts on the project’s engage page and incorporate commissioner feedback in the concept‑design phase.

The presentation spanned screening methodology, volume/speed data, corridor categorization, cross‑section options (separated bike lanes, dedicated transit lanes, transit+bike combinations), target speeds and mitigation strategies to support mode shift.

What happens next: staff said the team will refine concept designs for priority locations, coordinate near‑term actions with ongoing city projects (maple/stadium, Green and Plymouth work) and hold a fall open house before a final report is prepared later in the year.