The Effect of Speed Limits on Road Traffic Accidents
The effect of Speed Limits on
Road Traffic Accidents
Summary
An experiment was carried out to investigate the effect of speed limits on road traffic accidents. The investigation took place in Sweden during the summers of 1961 and 1962 and lasted for 92 days in each summer. For part of the 92 days general speed limits of 90km/hr or 100km/hr were imposed, for the rest of the time they were not. The number of accidents resulting in personal injuries at the end of each 92-day period was reported to the police. The purpose of this report is to see if, and to what extent the number of accidents is reduced when speed limits are in place.
Several key findings emerged from the exploratory analysis. Firstly, mean analysis on the number of accidents relative to the presence of speed limits suggests that limits do reduce the number of accidents. The mean number of accidents with limits was -18.9 and 18.4 in 1961 and 1962 respectively compared with 23.9 and 22.5 without limits. Looking at these figures there is also an indication of there being fewer accidents on average in 1962 than 1961. In total, across both years, the number of accidents with limits in place was 18.4 per day compared to 23.4 without limits - this is 5 more accidents per day without limits.
With reference to the scatter plots there appears to be no link between the day number (1-92) and the number of accidents. The plots are randomly scattered and suggest no trends or correlations.
The Poisson modelling procedure provided more detailed results. The two best models were models 7 and 8 (see table 2, p.10). Model 7 considered the factors Day, Year, Limit and the interaction term Year*limit. The terms limit and year*limit were highly significant with p-values of 0.03 and 0.02 respectively. These low p-values represent the probability that the observed relationship between variables occurred by chance
Road Traffic Accidents
Summary
An experiment was carried out to investigate the effect of speed limits on road traffic accidents. The investigation took place in Sweden during the summers of 1961 and 1962 and lasted for 92 days in each summer. For part of the 92 days general speed limits of 90km/hr or 100km/hr were imposed, for the rest of the time they were not. The number of accidents resulting in personal injuries at the end of each 92-day period was reported to the police. The purpose of this report is to see if, and to what extent the number of accidents is reduced when speed limits are in place.
Several key findings emerged from the exploratory analysis. Firstly, mean analysis on the number of accidents relative to the presence of speed limits suggests that limits do reduce the number of accidents. The mean number of accidents with limits was -18.9 and 18.4 in 1961 and 1962 respectively compared with 23.9 and 22.5 without limits. Looking at these figures there is also an indication of there being fewer accidents on average in 1962 than 1961. In total, across both years, the number of accidents with limits in place was 18.4 per day compared to 23.4 without limits - this is 5 more accidents per day without limits.
With reference to the scatter plots there appears to be no link between the day number (1-92) and the number of accidents. The plots are randomly scattered and suggest no trends or correlations.
The Poisson modelling procedure provided more detailed results. The two best models were models 7 and 8 (see table 2, p.10). Model 7 considered the factors Day, Year, Limit and the interaction term Year*limit. The terms limit and year*limit were highly significant with p-values of 0.03 and 0.02 respectively. These low p-values represent the probability that the observed relationship between variables occurred by chance