Conceptual Layout

The intersection of West Court Street and Dye Street was included in the early preliminary engineering phase with support from the Genesee County Road Commission and Flint Township due to intersection 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 Two intersection.

During the skim analysis, it was observed that there were 14 angle crashes and 0 head on left turn crashes over the 5-year period. These crashes resulted in one fatality, one type A injury, zero type B injuries, and seven type C injuries at the intersection.

The intersection of West Court Street and Dye Street is an all-way stop control intersection. Stop signs and overhead flashing beacons are present for all approaches. West Court Street runs east/west and is a two-lane roadway with one lane in each direction. Dye Street runs north/south and is a two-lane road with one lane in each direction. The intersection is located within a residential area with residences surrounding the intersection.  An aerial of the existing intersection can be seen in the picture 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 and PM peak hours, except for the northbound Dye Street approach in the PM peak hour which is LOS D.

The 95th percentile queue lengths were reviewed at the intersection and results showed that the approaches experienced a maximum queue length of 66 feet (3 vehicles) during the AM peak hour and 144 feet (6 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 southwest, southeast, and northeast quadrants of the intersection. An overhead power pole is located in the southeast quadrant and may be impacted by the proposed roundabout. A concept design exhibit for this intersection can be found in the slide above. During subsequent steps in the design process, the roundabout could potentially be shifted to the northeast in order to improve driveway access on the west leg of the intersection. This would be subject to discussions with the owner of this property. 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 0.7 vehicles during the AM peak hour and 1.9 vehicles in the 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 $1.14 million in year 2025 dollars. This cost includes a 20 percent contingency and 3 percent annual inflation. A full breakdown along with all assumptions can be found in Appendix 3 of the full report below.

Potential funding sources for this improvement could include regular road improvement funding, safety funds, or an earmark. A TOR was computed with a result of 6.14.

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