Impact of driver speeds on collisions

A UK road authority received frequent reports of collisions at a roundabout. They wanted to understand why loss-of-control collisions were occurring on the northbound in-slip lane just before the roundabout location. 

Using Path Analysis, Compass data showed drivers were taking the bend of the in-slip lane at high speeds and g-forces, causing friction loss. G-force steering data showed harsh left-hand swerving.

Speed vs steering g-forces showed that some steering g-forces ranged from -0.3 to -0.4, falling above the 85th percentile and safe majority. However, while most g-forces occurred below the unsafe threshold of 0.47, several swerving events occurred at high speeds of above 60km/h.

Speed data also showed that the 85th percentile travelled at speeds over 69km/h (43 mph) around the bend. While vehicles do slow down briefly at the bend, the combination of high speeds and road curvature results in friction loss events and collisions.

This helped the UK authority map where instances of near-misses (i.e. non-fatal crashes) occurred for early intervention and to prevent more serious crashes in future.