The purpose of this study was to determine how well older drivers understand the various configurations of protected and permitted left-turn signals that are currently in use. These included the Manual on Uniform Traffic Control Devices (MUTCD) standard protected and permitted left-turn arrangement with a 4-lens vertical stack, a 5-lens vertical stack, and a 5-lens doghouse arrangement. The permitted configurations used in Delaware (flashing red arrow), Michigan (flashing red ball), and Washington State (flashing amber ball), and a standard 3-lens configuration were also used.
This paper and pencil test used two illustrations per signal arrangement, including the intersection. The first illustration was used to depict the signal configuration, the second illustration indicated the same intersection with a changed light sequence (see figure 1). Subjects were asked to fill in the blanks from choices presented regarding what the drivers in each of the lanes should do. Choices included: stop or remain stopped; proceed straight; proceed straight or turn right; turn left when there is a large enough gap in oncoming traffic; turn left without stopping because you have the right of way; stop, but turn left when there is a large enough gap in oncoming traffic; and stop, but turn right when there is a large enough gap in oncoming traffic. Some of the scenes had separate left-turn signals, while others had shared signals. MUTCD regulatory sign R10-12 [Left Turn Must Turn Left on Green (ball)] was added to some scenes depicting several of the permitted left-turn configurations. Younger (under 65, n=121) and Older (over 65, n=126) licensed drivers participated in this study. Subjects were tested in Maryland, New York State, and Virginia.
Results
Researchers found that older drivers do not understand the protected/permitted left-turn signalization as well as younger drivers do. More importantly, neither group had a full understanding of left-turn signalization. Given this, researchers concluded that it would be inappropriate to specifically target countermeasures for older driver problems with signalization. They recommended that efforts be directed toward improving the comprehension levels of the entire driving population for intersection signalization.
A controlled field study was conducted using an instrumented vehicle to investigate the decision-reaction times and deceleration rates of younger and older drivers. Subjects drove on a closed course at 30 miles per hour (48 km/h) where they encountered 3 experimenter-controlled traffic signals. They drove this "loop" two times. At certain times or distances, the light would change from green to amber. Subjects had been instructed to behave as they normally would (stop or go through). On the third loop, subjects were asked to drive 20 mph (32 km/h) and to stop if the light turned from green to amber. On the fourth and fifth loops, the experimenter asked the subject to resume 30 mph (48 km/h), but stop if the light changed from green to amber.
Results
There were no significant differences between younger and older drivers in this study. The decision-reaction times were comparable, and similar numbers of drivers in both groups stopped on the amber phase in the first two loops. Deceleration rates of younger and older drivers were also comparable when drivers were stopping for a traffic signal. Based on these findings, the investigators determined that it is not necessary to change amber signal phase timing in order to accommodate older drivers.
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