Safety Evaluation of Continuous Green T Intersections

CHAPTER 9. SUMMARY AND CONCLUSIONS

The objective of this study was to evaluate the safety impacts of CGT intersections. Total, fatal and injury, and target (rear-end, angle, and sideswipe) crash types were considered. Data from Florida and South Carolina were used for this study to estimate CMFs for CGT intersections relative to conventional signalized T intersections. The propensity scores—potential outcomes—was used to estimate the CMFs. Genetic matching provided better matching results than NN or Mahalanobis matching. The CMFs were estimated using weighted negative binomial regression with the genetic matched data.

Based on the propensity scores-potential outcomes results (with genetic matching), the CMF point estimates for total, fatal and injury, and target crashes were 0.958, 0.846, and 0.920, respectively, suggesting that there was a potential reduction in crash frequency associated with the CGT intersection relative to the conventional T signalized intersection. Although the results were not statistically significant, it was likely due to the small sample rather than the lack of an effect. Because the CGT was not expected to compromise safety performance relative to a conventional signalized T intersection but affords improved traffic operational performance and fewer environmental impacts (lower vehicle emissions), it should be considered as a candidate alternative intersection form when conditions exist to effectively implement.

Based on the findings of this research and the literature review, CGT intersections are likely to be favorable over traditional signalized intersections when there are high through traffic volumes on the major street approach on the far side of the intersection (opposite the minor street approach). This approach could function as the continuous flow lane. The CGT intersection is also likely to be a favorable form if there is low cyclist demand and either no pedestrian demand or an alternative pedestrian crossing nearby.

The B/C analysis confirmed that the CGT is a cost-effective intersection design alternative to the conventional signalized T intersection (based on the point estimates of the CMFs). The B/C ratios for both asphalt and concrete pavements, as well as 35 and 55 mi/h posted speed limits on the major road, produced B/C ratios that significantly exceeded 1.0.

Potential Issues with CGT Intersections

Throughout the course of the present study, it was learned that several CGT intersections were being converted to conventional signalized T intersections in Florida. Anecdotal feedback indicated that non-motorized users at these locations have expressed concern with the high-speed, continuous flow lanes on the major approach. Pedestrians and bicyclists wishing to cross from the minor street approach to the far side of the high-speed continuous flow lanes may have difficulty identifying adequate gaps. As such, implementation of the CGT intersections at locations with anticipated pedestrian and bicycle users should be weighed against the operational and environmental benefits.