Conceptual Layout

The intersection of Coutant Road and Elms Road was included in the early preliminary engineering phase with support from the community due to intersection operations and safety concerns. This intersection is included in the 153 intersections that passed the skim analysis for experiencing crashes correctable by a roundabout and is a secondary analysis Tier Three intersection.

During the skim analysis, it was observed that there were nine angle crashes and one head on left turn crash over the 5-year period. These crashes resulted in zero fatalities, zero type A injuries, zero type B injuries, and eight type C injuries at the intersection.

The intersection of Coutant Road and Elms Road is an all-way stop control intersection. Stop signs and overhead flashing beacons are present for all approaches. Coutant Road runs east/west and is a two-lane roadway with one lane in each direction. Elms Road runs north/south and is a two-lane road with one lane in each direction. A short (approximately 70-foot) right-turn lane exists on the eastbound Coutant Road approach. There is a church in the southeast quadrant. There are residences in the other quadrants. An aerial of the existing intersection can be seen in the photo above.

An operational analysis of the no-build condition was completed for the intersection using the 2045 forecast traffic volumes. The results of the analysis for future no-build conditions reveals that all approaches operate at LOS C or better in the AM peak hour with the exception of southbound Elms Road (LOS E). In the PM peak hour, the Elms Road approaches operate at LOS F, eastbound Coutant Road is LOS D, and westbound Coutant Road is LOS C.

The 95th percentile queue lengths were reviewed at the intersection and results showed that the approaches experienced a maximum queue length of 178 feet (8 vehicles) during the AM peak hour and 573 feet (23 vehicles) during the PM peak hour.

The operational results for future no-build conditions are presented in the table below.

A compact single-lane roundabout with an inscribed circle diameter of 100 feet would improve traffic operations and safety at this intersection. This design would have a fully mountable central island to facilitate truck movements with the smaller diameter. Compact roundabouts have been implemented over the past 5 years at several similar locations in Washtenaw County, Michigan, with positive results. It is likely that a small amount of permanent right-of-way acquisition would be needed in the northwest, southeast, and northeast quadrants of the intersection. A concept design exhibit for this intersection can be found in the slide above. If desired later in the design process, a standard single-lane roundabout with diameter of 130 feet or greater could be considered at this location. A larger roundabout could result in greater right-of-way impacts and cost.

An operational analysis of the roundabout (build) condition was completed for the intersection using Rodel software and the 2045 forecast traffic volumes. The results of the analysis for roundabout (build) conditions reveal that all approaches and movements at the intersection operate at LOS A during the AM and PM peak hours.

The 95th percentile queue lengths were reviewed, and results showed that all approaches would experience a maximum queue length of 3.7 vehicles during the AM peak hour and PM peak hour for the compact single-lane roundabout design.

The operational results for future roundabout (build) conditions are shown in the table below.

A roundabout appears feasible at this location, assuming GCRC can acquire the limited right-of-way that may be needed.

An opinion of probable cost was developed for the compact single-lane roundabout. The probable cost is $1.15 million in year 2025 dollars. This cost includes a 20 percent contingency and 3 percent annual inflation.

Potential funding sources for this improvement could include regular road improvement funding, safety funds, CMAQ, or an earmark. A TOR was computed with a result of 21.02.

For a complete breakdown of the estimate please review the full report below.