Human Factors: Drivers’ Speed Choice on Relatively Low-Speed Limit Roads

The human factor in speed selection while driving is always associated with road accidents. Drivers who drive too slow or too fast are both at risk of being involved in road accidents. This paper presents the findings of a study conducted to determine the drivers’ perceived safe speeds and the hazardous speeds while driving on single carriageway roads under free-flowing traffic conditions and subject to relatively low-speed limit regulation, i.e., 60 and 70 km/h. Speed and its associated data were collected at three locations, i.e., Jalan Kulai–Kota Tinggi, Jalan Skudai–Pontian, and Jalan Pekan Nenas–Kulai (i.e., Jalan Sawah). The speed data for more than 2,300 vehicles were gathered using a speed radar meter. The data was analysed based on two categories of vehicles, namely light vehicles and commercial vehicles. The threshold for the hazardous speed is represented by the speed at the 15th percentile of a speed curve, and the 85th percentile speed represents the perceived safe speed. The analysis results show that the 85th percentile speed for all vehicles at each road segment is 81–85 km/h, which is well above the speed limits posted at each road segment involved in the study, i.e., 60 and 70 km/h, respectively. The hazardous speed on road segments with 70 km/h posted speed limit based on the aggregated data at each road segment is 57 km/h, i.e., about 13 km/h below the speed limit posted at the corresponding road segments. The hazardous speed due to commercial vehicles on the same road segments is 46–49 km/h, i.e., 21–24 km/h below the posted speed limit of 70 km/h. For road segments with a speed limit of 60 km/h, the data showed that most light vehicles travelled at speeds higher than the 60 km/h speed limit. Consequently, the hazardous speed representing all types of vehicles is about 57 km/h, which is slightly lower than the posted speed limit of 60 km/h. On the other hand, the hazardous speed due to commercial vehicles is just 10 km/h below the posted speed limit of 60 km/h, i.e., 50 km/h. The study showed that most drivers appeared challenging to adapt to a speed limit of 70 km/h or lower. As a result, the range of safe speed for the drivers to travel without violating the speed limit is relatively small because the hazardous speed due to commercial vehicles is relatively high compared to the respective speed limits.