MDOT single-point interchange in Novi, Michigan

Jim Kerwin
CEO, Kerwin Construction Co., Inc.
Westland, Michigan

A radically different design for an interstate highway interchange is being built on I-96 and Beck Road in Novi, Michigan. The concept creates a single traffic focal point at the center of the bridge above the expressway. The exiting and merging expressway traffic uses a total of four ramps with splits close to the crossroad without the traditional 360-degree turn for half the exits. The interchange shape reduces the land requirements with a narrower, smaller footprint.

The single-point interchange permits one stopping point to control traffic movement. Because the entering and leaving traffic approaches the intersection at a sharp angle and very close to the bridge center, it is necessary to have part of the interchange roadway over the bridge span. The design uses a single, very wide bridge structure to support the traffic rather than a normal width bridge with four little bridge corners. Each side of the bridge at mid-span is not used as part of the roadway function and is constructed as a matter of economy and convenience. This creates a problem of how to manage traffic so that drivers use only the intended roadway portion of the bridge.

The method selected for avoiding unintended vehicle use of the raised shoulder in the wide center section was to create a visual identity for the shoulder area with color and texture. No sign necessary, just an eight-food-wide curved strip of contrasting earth tone split Belgian block surface behind a low-rolled curb. Between the rough-looking Belgian block walk and the bridge railing is a large field of tan sidewalk-looking area. This project is located where the heavy commuter traffic dominates and there is very little pedestrian traffic to cross the bridge.

The tan shoulder is integrally-colored, broom-finished concrete with an MDOT 45D mix design. In order to place the concrete over epoxy-coated welded mesh with an almost 50-foot-wide center section and with minimal saw-cut joints, the 6" slump concrete was pumped. The mix design specifies #675 Type I cement, WR-91 retarder, Catexol 3500N medium range water reducer, and colored with Scofield Chromix. Broom finishing was accomplished with a double broom frame pulled by rope.

The eight-foot-wide running bond Belgian block strip is colored concrete with a stamped surface. This surface used the same integrally colored mix design plus three additional dry shake surface hardening colors. Good timing and a surface evaporation retarder were needed in order to manage stamping with the combined effects of high cement content, integral color, retarders and a dry shake.

There are several single-point urban interchange projects (SPUI, pronounced "Spooey") planned for Michigan.

The Michigan Department of Transportation awarded the first phase of the project to Prince Bridge and Marine, LTD. Mullendore & Romer/Kerwin Construction Co. Inc. poured the decorative horizontal surfaces. The project should be ready for service in the summer of 2005.

Jim Kerwin can be reached at (734) 422-1200 or at dankerwin@sbcglobal.net.