Case Studies

US 23 Lee Road
Livingston County, MI

Mr. Johnson was the roundabout design engineer responsible for the capacity analysis and horizontal design of what is the most complex system of roundabouts in the US at this time. These roundabouts handle approximately 8,000 vph and opened in 2006.

Signal alternatives were found to have inadequate capacity, resulting in excessive delays and potentially dangerous backups on freeway ramps. The double roundabout configuration at the southbound ramp terminals accommodates the five entries and exits with minimal circulating flow –increasing intersection entry capacity and reducing crash potential.

High-capacity roundabout intersections allowed a major interchange capacity improvement, while deferring the high cost of widening the bridge over US-23. This is an excellent example of placing capacity where it’s usually needed – at the intersections - while maintaining narrow connecting roads between intersections.

Highway 78/92 Intersection
Mount Horeb, WI

Mark was the lead engineer responsible for this urban intersection project, from initial analysis of alternatives, through the public outreach and decision-making process, to final design and construction. Compared to the signalized option, the roundabout avoided residential impacts and provided safer business access near the intersection. The compact urban design will serve 2,600 vehicles per hour, despite tight constraints on all four corners. The roundabout opened May 30, 2004. Read more...

Highway 30/Thompson Drive Interchange
Madison, WI

Mark was the lead engineer for this urban intersection/interchange project from concept through final design and construction. Mark completed the alternatives analysis and led the public outreach effort and decision-making process.  The design hour volumes of these two roundabouts are 4,700 and 2,700 vehicles.  The two roundabouts opened October 22, 2004. Read more...

Highway 54/ 2nd Street Intersection
Wisconsin Rapids, WI

Mark was responsible for review of the final horizontal geometry, signing, and pavement marking design and field layout for this constrained urban reconstruction project.  The design hour volumes are 2,500 vehicles. Opened September 2004. Read more...

Roundabout Presentations (PDF's)

Highway 78/92 Intersection
Mt Horeb, WI

Highway 30/Thompson Drive
Madison, WI

Highway 54/2nd Street Intersection
Wisconsin Rapids, WI