Route 115 Safety and Signal Improvements – Natural Bridge Road

TREKK’s work in the Route 115 Natural Bridge Road corridor began with a 2017 project to design 14 new traffic signals to replace signals that had reached the end of their useful life. The project limits extended from Euclid Avenue to N. Florissant Road and included signal design, ITS improvements, utility coordination, ADA improvements and striping. 

In 2018, TREKK began the study and design of safety and roadway improvements along Route 115 from Darby to I-70 in the city of St. Louis. The Federal Highway Administration classified the corridor as one of the highest crash rates in the country. Fatality rates, including those involving pedestrians, placed the corridor in the highest risk category.  

The safety study included a review of the roadway safety audit completed by MoDOT and the Crash Modification Factors (CMF) Clearing House to identify countermeasures to reduce crash rates. TREKK analyzed crash reports and created heat maps to identify hot spots along the corridor where the most crashes occurred. We considered the severity, classification, time of day and roadway condition of crashes during the analysis. Crash modification factors were also reviewed to investigate other potential traffic calming concepts. 

The areas identified as hot spots were then used to determine where to implement traffic calming strategies to improve corridor safety. These strategies included three roundabouts, a road diet, sidewalk reconstruction, raised center medians, offset left turn lanes with raised splitter islands, bump outs and four midblock crossings. The midblock crossings included bump outs, raised center medians with angled cut-thrus and rectangular rapid flashing beacons. 

Existing signalized intersections were also improved, including one full rebuild of an existing signalized intersection. TREKK also proposed the relocation of bus stops as needed to improve safety, as well as the reconstruction of bus pads to achieve ADA compliance. 

An early review to assess the effectiveness of the countermeasures, one year after construction was complete, indicated a more than 50 percent reduction in crash rates in the corridor sections with hardscape improvements.