As data are extracted from the Traffic Management Sector-Specific Incident Case Data Report from the Guangdong Provincial Security Department, which is the only official source of cross-sectional traffic accident data available in the Province, data quality can be assured. However, data are of the crash-injury severity type, it inherits the general problem of under-reporting minor injury and property damage only (PDO) accidents, and hence the possible bias in the parameter estimates due to such under-reporting might exist. Furthermore, issues such as omitted variable bias, endogeneity and within-crash correlation should be aware of when looking into the results (Savolainen et al., 2011).