The effects of combining reduced luminance and increased blur on older driver speed and visual acuity

Drivers may be at more risk to themselves and other roadway users when vision is blurred or when luminance levels are reduced. Past research has investigated these visual conditions separately, finding that each degrades acuity without severely impairing steering ability. However, it is unknown how reduced luminance in combination with increased blur will affect driving performance. This study sought to quantify this combined effect on older adults' comfortable driving speed and visual acuity by testing 10 participants in a driving simulator. The majority of the luminance and blur conditions are comparable to those the driving population may realistically encounter. Participants were asked to drive the speed at which they feel comfortable and could stay within their lane without using the speedometer. To ensure participants followed the instructions to stay in their lane, a percentage-of-time-in-lane measure was used to confirm no differences in steering performance existed across conditions. The older adult drivers only slowed down during the extreme blur condition; however, visual acuity was impaired by each manipulation. Interestingly, after the training conditions requiring a speed above 50 mph, drivers were given the opportunity to choose their speed and dramatically slowed down. This unexpected finding illustrates an important difference in what aging drivers choose to do in comparison with what they can do. This finding has important applied implications.