Impact of Taillight Width on Closing Distance Recognition

Introduction Summary

Front-to-rear crashes account for a large percentage of fatal collisions in the United States. While many of these are attributed to driver error (such as inattention), a significant cluster is related to the human visual system’s limitations in depth perception during motion, specifically the inability to accurately discern the combination of closing distance and closing speed at greater distances.

This research aimed to determine how the width of a lead vehicle’s taillights affects a driver’s perception of distance and speed. This is a critical safety factor because certain vehicles, like bobtail tractors (trucks without trailers), present a narrower taillight profile than standard passenger vehicles. The study addressed the known limitation that drivers are generally poor at estimating the longitudinal distance, velocity, or acceleration of vehicles moving in the same direction, especially at night when taillights are the primary visual cue.

Methodology Summary

The study utilized a visual perception experiment involving observers with both Commercial Driver’s Licenses (CDL) and non-commercial licenses. Participants were shown two 4-second video clips of a lead vehicle (LV) at night on an unilluminated two-lane highway, ensuring the taillights were the salient stimulus.

The LV was consistently closing at a speed of 72 km/h (45 mph) from initial distances ranging from 91 m (300 ft) to 457 m (1500 ft).

The independent variable was the taillight configuration:

1. Standard Taillights: A width of 1.7 m (5.4 ft).
2. Narrowed Taillights: A width of 0.4 m (1.43 ft), chosen to simulate the appearance of vehicles like bobtail tractors.

Using a Latin Square Design, every combination of distance and taillight configuration was tested. After viewing the paired clips, observers answered three main questions to test their visual perception: whether the vehicles were closing or separating, which vehicle was perceived as closer, and which had the quickest closing speed.

Results Summary

The results demonstrated that the perceived taillight width significantly influenced a driver’s judgment of distance and speed, confirming a visual system limitation.

• Perceived Distance: Observers consistently and incorrectly perceived the narrower taillight configuration as being farther away than the standard taillight configuration, even when the vehicles were at the same actual distance. This perceptual error persisted when comparing different distances.
• Perceived Speed: Observers perceived the wider taillight vehicle to be closing faster than the narrow taillight vehicle, particularly at distances closer than 128 m (420 ft).
• Closing Speed Accuracy: Despite the actual closing speed being a constant 72 km/h in all clips, only a minority of drivers could accurately judge the speed. Drivers often confused perceived proximity with actual speed, relying on the visual cue of distance over speed.
• Driving Experience: CDL drivers performed no better than non-commercial drivers in judging the distance of the narrow taillights. This finding supports the conclusion that the failure to recognize these closing thresholds is a fundamental human visual limitation (a perception failure) rather than merely a factor of driver inexperience or inattention.

References Cited

• Braunstein, M. L., & Laughery, K. R. (1964). The relative contribution of differentiation and retinal image size to the perception of simulated visual depth. Journal of Applied Psychology, 48(4), 227-234.
• Dingus et al., (2006). The 100-Car Naturalistic Driving Study, Phase II (DOT HS 810 593). Washington, D.C.: National Highway Traffic Safety Administration.
• Fisher, D. F., & Hall, R. (1976). The effect of stimulus on distance perception. Vision Research, 16(10), 1145-1150.
• Gray, R., & Regan, D. (2000). Visual mechanisms of loom-based time-to-contact judgments. Perception, 29(12), 1435-1447.
• Hoffman, E. R., & Mortimer, R. G. (1996). Driver rear vision with conventional and wide rearview mirrors. Human Factors, 38(2), 246-254.
• Janssen, W. H., Jelen, J. L., & Povel, D. (1976). Car-following performance with and without braking display (Report No. M-26). Soesterberg, Netherlands: TNO Institute for Perception.
• Janssen, W. H. (1977). The perception of relative motion in the car-following situation (Report No. M-23). Soesterberg, Netherlands: TNO Institute for Perception.
• Knipling, R. R., Mironer, M. S., Lee, S. E., Mehrer, M. W., & Tijerina, L. (1993). Integrated collision avoidance systems for the automotive highway (SAE Technical Paper 930554). Warrendale, PA: Society of Automotive Engineers.
• Lamble, D., Laakso, M., & Summala, H. (1999). The effect of driving experience on the perception of the lead car’s braking. Accident Analysis & Prevention, 31(3), 253-261.
• Lee, S. E., D. V. McGehee, and T. A. Dingus (2002). Study of rear-end crash warning effectiveness. Accident Analysis & Prevention, 34(5), 585-594.
• Lee, J. D., Olsen, E. C., & Wierwille, W. W. (2004). A model of driver response time to rear-end collision warnings. Human Factors, 46(4), 629-640.
• Markkula, G., Bärgman, J., Victor, T., & Lee, J. D. (2016). Glances at the road ahead during high-speed car following. Accident Analysis & Prevention, 93, 218-228.
• McGehee, D. V., R. H. R. T. R. T. R., & Dingus, T. A. (1997). Examination of driver’s collision avoidance behavior in a lead vehicle stopped scenario using a front-to-rear-end collision warning system (NHTSA Technical Report).
• Mortimer, R. G. (1972). Driver braking reaction times to rear-end collision situations (SAE Technical Paper 720090). Warrendale, PA: Society of Automotive Engineers.
• Mortimer, R. G. (1990). In search of a brake response time (SAE Technical Paper 900388). Warrendale, PA: Society of Automotive Engineers.
• Muttart, J. W. (2003). The relationship between relative velocity detection and driver response times in vehicle following situations (SAE Technical Paper 2003-01-0887). Warrendale, PA: Society of Automotive Engineers.
• Muttart, J. W., Kunkle, B. L., & Shauger, L. C. (2005). The relationship between relative velocity detection and driver response times in vehicle following situations (SAE Technical Paper 2005-01-0427). Warrendale, PA: Society of Automotive Engineers.
• Reason, J. (2000). Human Error: Models and management. Western Journal of Medicine, 172(6), 393-396.
• Sorock, G. S., Ranney, T. A., & Lehto, M. R. (1996). Motor vehicle crashes in roadway construction workzones: an analysis using narrative text from insurance claims. Accident Analysis & Prevention, 28(2), 131-138.
• Summala, H., Lamble, D., & Laakso, M. (1998). Driving experience and perception of the lead car’s braking when looking at in-car targets. Accident Analysis & Prevention, 30(3), 401-407.
• Terry, H. R., Charlton, S. G., & Perrone, J. A. (2008). The role of looming and attention capture in drivers braking responses. Accident Analysis & Prevention, 40(4), 1375-1382.
• Victor, T., Dozza, M., Bärgman, J., Boda, C.-N., Engström, J., Flannagan, C., Lee, J. D., & Markkula, G. (2015). Analysis of naturalistic driving study data: Safer glance patterns related to car-following. In Proceedings of the Human Factors and Ergonomics Society Annual Meeting (Vol. 59, No. 1, pp. 2095-2099). Los Angeles, CA: SAGE Publications.
• Fatal Analysis Reporting System (FARS). (n.d.). National Highway Traffic Safety Administration.