In early June of 2016, the Michigan House of Representatives passed House Bill 4423 that, if signed into law, would increase the statutory maximum speed limit on select rural non-freeway highways from 55 mph to either 60 or 65 mph. Since much of the Michigan non-freeway highway network is designed for compliance with posted speed limits of 55 mph, systemwide speed limit increases would likely result in substantial geometric upgrade costs, along with additional crashes, injuries, and fatalities. Consequently, shortly after the legislative speed limit policy debate began in Michigan in 2014, the Michigan DOT (MDOT) initiated research to proactively identify candidate rural highway segments for consideration in the event of a statutory speed limit increase. The primary objective was to identify locations that possessed comparatively low safety risks and where costly geometric upgrades, specifically horizontal or vertical realignment, would be avoided. Consideration was given to several safety, operational, and geometric factors. Ultimately, 12 factors and associated selection criteria were utilized to determine the candidate segments. These factors included: segment length, total crash rate, injury crash rate, severe (fatal and a-injury) crash rate, horizontal curvature, speed reduction zones, no-passing zones, K-8 schools, driveway density, lane width, paved shoulder width, and signalized intersections. Application of the candidate selection criteria to MDOT’s systemwide non-freeway network yielded 772.8 miles along 33 candidate segments, which represented approximately one-eighth of the network mileage currently posted at 55 mph. Subsequent comprehensive engineering, safety, and operational analyses are recommended for each candidate segment prior to any increase in the speed limit. Furthermore, to avoid substantial geometric upgrade costs, speed limit increases are specifically not recommended for segments requiring horizontal or vertical realignment to achieve design speed compliance.
Dr. Timothy J. Gates is an associate professor of transportation within the Department of Civil and Environmental Engineering at Michigan State University. Dr. Gates has extensive research experience in traffic engineering, traffic operations, traffic safety, and driver behavior. During his more than nine years as faculty at MSU and Wayne State University, he has served as Principal Investigator (PI) or co-PI on numerous grant awards from agencies that include the Michigan Department of Transportation, Michigan Office of Highway Safety Planning, FHWA, and NCHRP. This research has led to the publication of 46 peer-reviewed articles in refereed journals, with an additional 25 peer-reviewed conference proceedings. Beyond his research activities, Dr. Gates is chair of the Transportation Research Board Committee on Traffic Control Devices (AHB50) and is also a member of the Operational Effects of Geometrics (AHB65) Committee. Prior to joining Michigan State University in August 2015, Dr. Gates was a civil engineering faculty member at Wayne State University (WSU) for eight years. Dr. Gates earned his Ph.D. in civil engineering from the University of Wisconsin-Madison in 2007 and master’s and bachelor’s degrees in civil engineering from Michigan State University in 2000 and 1999, respectively.