\section{Acknowledgements}

The authors would like to acknowledge the funding of the Québec road safety research program supported by the Fonds de recherche du Québec -- Nature et technologies, the Ministère des Transports du Québec and the Fonds de recherche du Québec -- Santé (proposal number 2012-SO-163493), as well as the various municipalities for their logistical support during data collection. Shaun Burns, a Masters student at McGill University was also instrumental in the collection of video data.