Objectives: This paper aimed to (i) differentiate the effects of contributory factors on crash risks related
to different transportation modes, i.e., motor vehicle, bicycle and pedestrian; (ii) explore the potential
Received in revised form contribution of zone-level factors which are traditionally excluded or omitted, so as to track the source
Accepted 13 October 2016 of heterogeneous effects of certain risk factors in crash-frequency models by different modes.