Determining Impact of Road Lighting on Motorway Capacity

The subject of this paper is the impact of road lighting on the capacity of uninterrupted motorway sections. A capacity estimation method was used that is based on extrapolation of the free-flow part of the fundamental diagram representing the relation between flow rate and density. The method assumes that the density at capacity is not affected by illumination, which implies that capacity shifts are fully the result of speed changes. The method was applied in a Dutch case study. In a before-and-after study, the impact of road lighting was estimated for two directions of one road section. Capacities of the road section were estimated for various periods of the day. Capacities during the daytime did not differ significantly before and after introduction of lighting. Nevertheless, during nighttime a significant increase in capacity of about 2.5 percent was found.