Bicycling accidents are a major traffic safety problem and are deemed “an unacceptable human and social price for EU citizens”. One of the major causes for bicycling accidents is loss of balance. A related influencing factor is alcohol intoxication. It is a primary, long term, safety objective to develop safety systems for the cyclist. The present work aimed to understand how to measure cyclists’ instability via steering and leaning inputs, while considering that steering and leaning might vary depending on the cycling task being performed. The long term objective is to develop an ARAS for bicyclist (compare ADAS for cars).

Of 28 participants, 19 were given doses of alcohol up to 1.0 ‰ and 9 remained sober (control group). Breath alcohol concentration was measured. The participants repeated the cycling test track session five times, and each session contained four laps every time (with each block lasting 35 minutes). The track session contained three different tasks: cycling slalom, straight, and slowly. Speed, yaw rate, and roll rate were assessed continuously. Alcohol intoxication was 0.00 ‰ at baseline, 0.19‰, 0.47‰, 0.71‰, and 87 ‰ at the last test session.

The rather simple measurements used can detect instability. Assuming there is a strong relationship between alcohol concentration and cycling stability, we were able to identify three measures sensitive in discriminating between stable and unstable cycling performance. These measures were yaw rate at level 3 (> 150 °/s) when cycling slalom, yaw rate at level 1 (> 50 °/s) when cycling straight and roll rates at levels 1–3 (> 5 °/s, 10 °/s, and 15 °/s) when cycling slowly. Some useful steps towards the development of an ARAS with instability warnings have thus been taken. The study represents a small step towards a safety system for cyclists.