Converting an intersection into a roundabout improves motor vehicle safety, but a similar safety effect is not found for car bicycle collisions.
Due to the fact that safety studies are observational (non-experimental), there are confounding factors, which influence the accident occurrences and, therefore, should be accounted for in the estimation of a real safety effect of the treatment.
The finding from this study - that roundabouts with separated cycle tracks had a greater safety effect than those with on-road marked bike lanes or no bicycle infrastructure - is consistent with other research.
On-road marked bike lanes were found to have a positive safety effect in five studies, consistently reducing injury rate, collision frequency or crash rates by about 50% compared to unmodified roadways [ 61, 62, 65- 67].
It is also possible that the null result may actually be indicative of a positive safety effect of the guards, as pedestrian volumes are likely to increase at a specific location with the implementation of a school crossing guard; thereby increasing pedestrian exposure to traffic.
Thus, a demand for safety effect estimates of road infrastructure improvements and other safety-related measures is expected to grow in the future.
For such a treatment, the estimated safety effect will reflect a combined impact of all the infrastructure changes applied, without the possibility of further subdivision into separate components.
These changes in driver behaviour can be linked to an increased road safety effect, in line with the commuters' sense that the rumble strips were a traffic safety measure.
The model was applied to assess the safety effect of a new design of a bicycle crossing.
A literature review on the safety effect of roundabouts, prepared for the 18th Workshop of the International Co-operation on Theories and Concepts in Traffic Safety [ 77], came to similar conclusions.
