The effects of telephoning while driving were studied in three different traffic conditions, i.e. in light traffic on a quiet motorway, in heavy traffic on a four-lane ring-road, and in city traffic. Twelve subjects, unfamiliar with mobile telephones, drove an instrumented vehicle for one hour each day during three weeks and while in each of the three traffic conditions, had to operate the mobile telephone for a short while. To ensure a fixed "heavy traffic load" in the second condition, the subjects were instructed to follow another instrumented vehicle (at a safe distance). The Volvo 245 GLD cars were modified so that the following data were collected: (a) the vehicle's lateral position relative to the carriageway marking; (b) heartrate; (c) steering wheel movements (using a potentiometer); (d) testvehicle speed (by doppler radar); (e) distance of the car in front (by infrared laser); (f) number of times the subjects checked the rear mirror (by video camera). The results showed a significant effectof telephoning while driving as opposed to normal driving (i.e. notinvolving telephone conversation), on the effort subjectively measured by an effort scale and objectively measured by heartrate indicesand on some of the measured arameters of driving performance. One half of the subjects had to operate the telephone manually, the other half performed the telephone task with a handsfree mobile telephone set. The subjects who operated the handsfree telephone showed better control over the test vehicle than the subjects who operated the handheld telephone, as measured by the steering wheel movements. Also, a clear improvement over time in the course of the 15 test days was found for some of the measrements. As a consequence of the results, some advice concerning mobile telephoning can be given to authorities, manufacturers, and users.
Abstract