The effects of vertical speed control devices on vehicle speed and noise emission

Vertical speed control devices have been found to effectively reduce vehicle speeds, particularly when used in a sequence. The placement of a device from the entrance of a street and from another device is crucial in maintaining low speeds throughout a street. Studies were carried out to identify the design factors that significantly influence speed, and to find appropriate regression models for estimating 85th percentile and mean speeds along local streets calmed by speed humps and speed tables. Results show that, aside from the type of device, the most significant factor in determining speeds on streets with vertical deflections is the spacing between devices and the spacing of devices from the street entry. Also, S-curve models were found to best represent the relationships between inter-device speeds and spacings. One of the drawbacks is the noise produced when vehicles move over humps. To investigate the noise effect, studies were conducted on two Watts profile humps with different heights, and a flat section of road. Results suggest that at a reference speed of 25 km/h, noise levels for vehicles passing the 100 mm hump were 3.6 dBA higher than those produced by the 75 mm hump, but were interestingly similar to those produced on the flat section. The speed and noise models developed in this research offers technical information to help practitioners manage vehicle speed and noise on local streets through the design of speed humps and tables.