In summary the objective of this paper is twofold: (1) to examine
the effects of a host of contributing factors including both macro-scopic and microscopic factors on crash occurrence with respect
to different transportation modes; (2) to shed further light on the
contribution of the macroscopic factors which are traditionally
excluded or omitted variables, to tracking the source of hetero-geneity effects in coefficient estimators of regularly used variables
and improving the model performance in crash-frequency analysis
related to different modes.