Intersection Conflict Warning Systems Should Avoid Using Messages Such as “Traffic Approaching When Flashing” Since the Signs May Not Always Flash.
Minnesota, Missouri, and North Carolina Provide Lessons on Installation of Intersection Conflict Warning Systems.
Made Public Date


United States


United States


North Carolina
United States

Safety Evaluation of Intersection Conflict Warning Systems


The Intersection Conflict Warning Systems (ICWSs) strategy involves installing vehicle detectors, warning signs such as flashing beacons and variable message signs on the major and/or minor approaches of unsignalized intersections to detect and alert motorists about conflicting vehicles on adjacent approaches. This study evaluates ICWSs at four-legged rural two lane stop-controlled intersections. The objective was to estimate the safety effectiveness of this strategy as measured by crash frequency. Geometric, traffic, and crash data of this type of intersections with ICWS installations in Minnesota (MN) (13 intersection installations), Missouri (MO) (14 intersection installations), and North Carolina (NC) (66 intersection installations) were used to conduct the evaluation of their safety effectiveness. The categories of ICWS installations considered for this study included; i) Overhead signs and flashers at the intersection on the major; loop detector on the minor approach, ii) Overhead signs and flashers at the intersection on the minor approach; loop detector on the major approach, iii) Post-mounted signs and flashers in advance of the intersection on the major; loop detector on the minor approach and post-mounted signs and flashers at the intersection on the minor approach; loop detector on the major approach, iv)Locations with a combination of category (i) through category (iii).

Lessons Learned

Based on the installation details of ICWS provided by Minnesota, Missouri, and North Carolina, the following lessons are summarized:

  • Expect operational challenges. Especially for prototype systems, keeping the system operational 24/7 could be a challenge due to staffing gaps in monitoring the system, technical issues or maintenance problems. 
  • Be wary of what your message sign says. For the warning message, there are various options, but the “traffic approaching when flashing” is likely to be avoided due to litigation concerns (the sign may not always flash).
  • Take a dynamic and responsive approach to safety. If a continued trend in certain types of collisions (such as angle collisions) is observed after ICWS installation, it may be warranted to modify the access and potentially implement a different intersection design for improved safety.
  • Place warning signs appropriately following MUTCD Guidelines for better perception response time. In some cases, if the intersection was located on a curved roadway segment, the flashers could be placed in advance of the intersection on the major approach so that drivers could better see the warning.
  • Install ICWS only where it is warranted to save time, money, and effort. Focus on sites with higher opportunity for crash reductions. 
Goal Areas
System Engineering Elements