This study used data from 132 MUTs (264 U-turns) from the State of Michigan to investigate the safety aspects of access control at the U-turn crossovers. Some of the U-turns were access controlled, while others had access. Crash prediction models were estimated utilizing mixed-effects negative binomial regression. The models produced useful results but also had some counterintuitive results. The project team used their best judgment to develop recommended CMFs for selected features of the U-turns. Here is an overview of some of the key findings from the study:
- While the count of access points in the merging directions (where U-turning vehicles merge with oncoming through traffic) were associated with higher crash likelihoods 4.45 percent, 6.94 percent, and 8.67 percent for total, fatal and injury (FI), and property damage only (PDO) crashes, respectively, compared to no access points in merging direction. that in diverging direction (where U-turning vehicles leave the mainline to enter the U-turn segment) was associated with higher likelihood by 5.53 percent for only PDO crashes, compared to no access points.
- Among the different access point types, counts of side streets were associated with higher crash likelihoods by 10.77 percent, 6.05 percent, and 9.96 percent for total, FI, and PDO crashes, respectively, compared to no access points of these types.
- The variable representing whether there was an access point close to the U-turn crossover that allowed vehicle to make a left directly from the U-turn lane was found to be associated with greater likelihoods by 12.99 percent and 25.73 percent for total and FI crashes, respectively, compared to no such access points.
- Increasing U-turn radius was associated with slightly lower likelihood, by only 0.52 percent for total crashes, for each unit (ft) increase of U-turn radius.
- Increase in the number of through lanes at U-turns in the diverging direction was associated with a lower crash likelihood by 12.04 percent for FI crashes only.
Based on the recommended CMFs, U-turns lanes without left turns as well as higher number of through lanes in diverging directions could be suggested to improve the safety performance.
