A new study appeared in the journal Ophthalmic & Physiological Optics that has implications for the safety of both older drivers and pedestrians. It also highlights the inadequacies of current legal definitions of who is safe to drive. Those rules only account for visual acuity and not measures of real-world visual processing such as processing speed or useful field of view.
The researchers who authored the study sought to investigate the effects of driver age on the ability of the drivers to notice pedestrians at night and to determine and which aspects of visual performance can predict a driver’s ability to recognize pedestrians at night. The researchers took two groups of drivers: a group of visually normal drivers around the age of 24 and another group of drivers around the age of 72.
The researchers then measured the visual performance of drivers in a laboratory-based testing session. The parameters measured were visual acuity, contrast sensitivity, motion sensitivity and the useful field of view. Then the researchers recorded the distances at which drivers noticed pedestrians at night while the drivers drove along a closed road coarse.
The pedestrians walked in place, sideways to the oncoming vehicles. Some of them wore a standard high visibility reflective vest. Others wore reflective tape positioned on the movable joints such as shoulders, elbows, wrists, waist, knees and ankle. The latter is known as “biological motion”.
The results of the study were that the biological motion reflective strips made pedestrians easier to recognize when compared to the reflective vests and that older drivers had a significantly harder time noticing pedestrians compared to younger drivers:
driver age and pedestrian clothing significantly affected the distance at which the drivers first responded to the pedestrians. Older drivers recognised pedestrians at approximately half the distance of the younger drivers and pedestrians were recognised more often and at longer distances when they wore a biological motion reflective clothing configuration than when they wore a reflective vest. Motion sensitivity was an independent predictor of pedestrian recognition distance, even when controlling for driver age.
The night-time pedestrian recognition capacity of older drivers was significantly worse than that of younger drivers. The distance at which drivers first recognized pedestrians at night was best predicted by a test of motion sensitivity.
These findings may ultimately lead to new rules on the assessment of driver safety. Unfortunately, this is not likely to happen soon because other tests that have been shown to correlate to safe driving, such as contrast sensitivity function, and Useful Field of View are still not a part of any state-mandated driver tests. Even so, it is important for eye doctors to be aware of this information to properly counsel their older patients, who often come to them with complaints about feeling unsafe while driving.
The study’s results also suggest that for pedestrians to be safe at night, they should wear reflective strips at their movable joints to make themselves most noticeable to older drivers.
Ophthalmic & Physiological Optics: The Journal of the British College of Ophthalmic Opticians (Optometrists)
Seeing Pedestrians at Night: Effect of Driver Age and Visual Abilities Ophthalmic Physiol Opt 2014 Jun 02;[EPub Ahead of Print], JM Wood, P Lacherez, RA Tyrrell