Abstract
This article investigates the effect of ambient light level on traffic flow for different types of road user—pedestrians, cyclists, and drivers of motorized vehicles—using counts of traffic flow recorded by automated counters. Previous analyses have focused only on pedestrians and/or cyclists, in Arlington, Virginia (U.S.) and Birmingham (U.K.). The new data represent all three types of road user for one location (Cambridge, U.K.) and motorized vehicles in London (U.K.), Adelaide (Australia) and trunk roads in England. The effect of ambient light level was established using odds ratios to compare traffic flows in case and control hours, chosen to isolate the effect of ambient light from other factors of influence. The data for this analysis included the counts for 71,477,159 motorized vehicles, 89,392 pedestrians, and 66,925 cyclists. It was found that darkness leads to significant reductions in pedestrians and cyclists but does not have a significant effect on the number of motorized vehicles.
Highlights
This article investigates the effect of ambient light level on traffic flow for different types of road user—pedestrians, cyclists, and drivers of motorized vehicles—using counts of traffic flow recorded by automated counters
A better understanding of how change in ambient light level influences traffic flow would inform consideration of the potential benefits of road lighting after dark, including how the change in road traffic collision (RTC) risk is influenced by any changes in exposure
When the analysis considered the 13 days before and after clock change, the odds ratio (OR) of 1.72 suggested a significant reduction in pedestrian numbers after dark [13]. (Note that these are the OR for the early day and late dark control hours in that study: see Uttley and Fotios, and Robbins and Fotios for analyses of how the choice of control hour influences the OR [13, 14])
Summary
This article investigates the effect of ambient light level on traffic flow for different types of road user—pedestrians, cyclists, and drivers of motorized vehicles—using counts of traffic flow recorded by automated counters. The effect of ambient light level was established using odds ratios to compare traffic flows in case and control hours, chosen to isolate the effect of ambient light from other factors of influence The data for this analysis included the counts for 71,477,159 motorized vehicles, 89,392 pedestrians, and 66,925 cyclists. In relation to seasonal trend (Figure 2), the average hourly traffic flow for cars is fairly uniform across the year but with a slight increase in summer, while for cycles the seasonal variation is more significant with miles traveled being 75% higher in the summer months than in winter months These data are used for basic traffic flow analyses and do not isolate the impact of a single factor on travel behavior. Including control periods within the OR accounts for seasonal influences on traveler count such as the weather
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