Is a Protocol Needed for Measuring Aged Retroreflective Sheeting?

Introduction Summary

Nighttime driving poses a significant safety risk, accounting for nearly 50% of US roadway crashes despite lower traffic volumes. This risk is amplified for large trucks; heavy trucks are involved in eight times more rear-end impacts at night than in daylight hours. The human visual system’s lower detection thresholds in the dark contribute to this problem.

In response, Federal Motor Vehicle Safety Standards (FMVSS) No. 108 mandated the use of Retro-Reflective Tape (conspicuity tape) on heavy trailers starting in 1993. However, the effectiveness of this sheeting degrades naturally with age and dirtiness. Crucially, no current federal or state regulations require in-use testing or refreshing of this retroreflective material. The study aimed to develop a quick, reliable measurement protocol and to assess how many in-use trailers currently fail to meet the minimum retroreflectivity standards, thereby addressing this critical safety gap.

Methodology Summary

The research was executed in two phases:

1. Protocol Development: This phase focused on creating a rapid, validated field measurement technique.
   • Ten in-use trailers were tested using a handheld retroreflectometer.
   • Measurements were taken “as found” and then immediately after the sheeting was wiped clean with a dry cloth to quantify the effect of dirtiness.
   • A detailed, full-trailer measurement process was compared against a proposed 10-to-15 minute sampling technique to validate the efficiency and accuracy of the faster protocol.
2. Field Study: The validated sampling technique was applied to a large, diverse sample of commercial vehicles.
   • A total of 191 randomly selected trailers were measured.
   • Data collection occurred at DOT inspection locations and rest areas across five different States to ensure geographical diversity.
   • The age of the trailer (model year) was recorded alongside the retroreflectivity measurements. The entire process per trailer took less than 15 minutes.

Results Summary

The results confirmed the study’s hypotheses regarding degradation and validated the simple testing protocol, revealing a widespread safety issue across the commercial fleet.

• Impact of Dirtiness: Simple cleaning of the sheeting resulted in an average increase in retroreflectivity readings of more than 1.3 times. Overall, accumulated dirt was found to decrease readings by approximately 25%.
• Protocol Validation: The fast 10-to-15 minute sampling protocol proved effective, showing statistical equivalence to the detailed, time-consuming readings. This validated the technique for field use by safety officials.
• Substandard Performance: The field study of 191 trailers showed a significant failure rate: 34% of all white sheeting readings and 26% of all red sheeting readings failed to meet the Federal Motor Vehicle Safety Standards (FMVSS) minimum retroreflectivity requirements.
• Age and Failure: The median age of the trailers was 9 years, and the results confirmed that increasing trailer age correlated with a higher probability of retroreflectivity falling below the mandated standard.

The research concluded that the failure rates are a widespread safety concern that will likely worsen as the trailer population ages. The simple, accurate test protocol developed is well-suited for use by law enforcement and safety officials, supporting the necessity of in-use maintenance and testing requirements for retroreflective conspicuity tape.

References Cited

• Morgan, C. (2001). The Effectiveness of Retroreflective Tape on Heavy Trailers (DOT HS 809 222). Washington, D.C.: National Highway Traffic Safety Administration.
• The study cites 2014 fatal crash statistics involving large trucks.
• The study cites a previous crash study on rear-end impacts involving medium and heavy trucks between 1987 and 2001.
• The study cites research by Morgan reporting on crash reductions associated with cleaned vs. dirty tape.
• Olson, P. L., Campbell, K., Massie, D., Battle, D. S., Traube, E. C., Aoki, T., Sato, T., & Pettis, L. C. (1992). Performance Requirements for Large Truck and Conspicuity Enhancements (Report No. UMTRI-92-8). Ann Arbor, MI: University of Michigan, Transportation Institute.
• Graving, J.S., Tyrrell, R.A., Balk, S.A. (2009). Quantifying the subjective brightness of retroreflective materials using magnitude estimations. Proceedings of the Fifth International Driving Symposium on Human Factors in Driver Assessment, Training and Vehicle Design.
• Muttart, Jeffrey W., Swaroop Dinakar, Gregory Vandenberg, and Michael Yosko. (2016). The Influence of Driver Expectation when Recognizing Lighted Targets at Nighttime. In Proceedings of the Human Factors and Ergonomics Society Annual Meeting, vol. 60, no. 1, pp. 489-493. SAGE Publications.
• Ziedman, K., Burger, W.J., Smith, R.L., Mulholland, M.U., and Sharkey, T.J. (n.d.). Improved Commercial Vehicle Conspicuity and Signalling Systems; Task II: Analysis, Experiments and Design Recommendations. (DOT-HS-806…).