Image-Based Remote Measurement of Retro-Reflectivity of Roadways Assets in the Daytime

One of the most effective and low-cost ways for improving nighttime driving safety of transportation systems is maintaining the traffic signs retro-reflectivity. The U.S. Federal Highway Administration (FHWA) has enacted new rules on the minimum level of retroreflectivity which compels agencies to measure the current levels of retro-reflectivity of traffic signs and develop plans for replacing or improving their condition. Current practices in assessing and measuring the retro-reflectivity of traffic signs, including handheld retroreflectometer and mobile technologies, are financially and practically infeasible because of their physical and technical constraints.

This research project explores and presents the possibility of an inexpensive, safe, and cost-effective computer vision method for remotely measuring the retro-reflectivity of traffic signs during daytime using High Dynamic Range (HDR) images. By capturing two images simultaneously during the daytime, the method simulates nighttime visibility for each sign and measures retro-reflectivity at a level of accuracy that is mandated by FHWA guidelines. The research project develops a remote retro-reflecto-meter that consists of a consumer-grade camera, flashlight, GPS receiver, and screen. An experimental test was conducted on different types of traffic signs with different levels of retro-reflectivity which are located at different distances in real-world conditions to validate the performance of the method. The results, compared with data collected from a standard retro-reflectometer, demonstrates the potential of the method in lowering costs, improving safety, perform during the daytime, and shorten time required for retro-reflectivity data collection.

The proposed technique is faster, cheaper, and safer compared to the state-of-the-art as neither requires nighttime operation nor manual sign inspection, particularly for overhanging signs which are hard to reach. The developed technique allows inspectors to carry around and measure retro-reflectivity levels during the daytime on foot. The technique can be mounted to and detached from a vehicle to be used by an inspector in the passenger seat. This study will provide an effective way for CalTrans to inspect and replace/repair defective signs and markings while avoiding expensive retro-reflecto-meters and nighttime visibility inspections. If CalTrans wants to implement the developed technology at a larger-scale, their research team will seek opportunities with CalTrans’ current vendors which aim to provide mobile asset management services to transfer the developed technology.