Dillon Funkhouser

Naturalistic Census of Cell Phone Use

One hundred eight drivers participated in a naturalistic field operational test. Each participant drove an instrumented passenger car for 6 weeks. Video data from the first week of driving for each participant were visually scored for all instances of cell phone use. These instances were divided into cell phone calls (conversations) and cell phone interactions that were not calls (visual or manual tasks involving the cell phone). Researchers examined 1,382 conversations and 2,149 visual or manual tasks. Participants were engaged in cell phone conversations 6.7% of all driving time and in visual or manual tasks involving a cell phone 2.3% of all driving time. Overall, conversations had a mean duration of 2.6 min, and participants engaged in conversations at a rate of 1.5 conversations per hour. Younger drivers were significantly more likely to be engaged in either type of cell phone task than older drivers and significantly more likely to be engaged in visual or manual tasks than middle-aged drivers. Drivers were more likely to initiate conversations and visual or manual tasks when stopped than at higher speeds; this finding may suggest a level of self-regulation. Furthermore, the finding suggests that estimates of crash risk that are based on assumptions that behavior observed in stopped vehicles translates to behavior in moving vehicles is incorrect and will result in overestimates of driver engagement in cell phone use.

Traffic sign legibility for different sign background colors: results of an open road study at freeway speeds

Transportation agencies have been considering the use of a purple sign background color to denote that the roadway is tolled. Prior studies have shown a driver preference for a unique color for the toll road category. Concerns about the legibility of purple signs have been raised due to their brightness and contrast ratio with a white legend. The current study performed an evaluation of the legibility and recognition of purple and green freeway guide signs during daytime and nighttime driving in the Houston, TX area. Forty-eight participants drove an instrumented vehicle in open traffic and read traffic signs along a toll road with purple signs on one segment and green signs on another. Results showed no significant difference in legibility distance between signs with purple and green backgrounds. An analysis of recognition distances for advance guide signs marking ramps to the toll road also showed no difference between purple and green signs. These results support the implementation of this new color without any loss in legibility.

Driving Performance and Driver Workload at High Speeds: Results from On-Road and Test Track Studies

As roadway agencies consider allowing higher speed limits, they must consider if assumptions about human performance built into roadway design formulas hold true at higher operating speeds. This paper presents a study of 14 drivers who drove both an open-road section and a test track course. The open-road route presented a natural experiment because it contained a long Interstate Highway section split roughly equally between sections with posted speed limits of 70 mph and 80 mph. On the test track, drivers were asked to maintain speeds of 60 and 85 mph for each of three nine-mile laps in which various in-vehicle tasks and a car following task were introduced in order to assess the effect of vehicle speed on driving performance. Subjective workload estimates were used for the test track tasks in addition to driving performance data. The results showed no major differences in driving performance across the different speeds tested.

An Examination of Naturalistic Windshield Wiper Usage

In the course of a field operational test, 96 participants drove instrumented vehicles from which driving data was recorded. Windshield wiper activity was examined in order to provide data regarding the naturalistic use of wiper systems. The results have implications for the design and durability of windshield wipers, wiper motors, windshields, and glazing treatments. Overall, wipers were used 8.6% of the time. When ambient lighting diminished, a shift towards higher wiper speeds was observed. Average headway time and range increased, and speed decreased, when wipers were engaged. Finally, middle-aged drivers used wipers more often than their younger and older counterparts.