Table 1.

Traffic flow variables and associated results in crash severity studies.

Study	Authors (year)	Considered traffic flow variable	Results
8	Yu and Abdel-Aty (2014)	Standard deviation of speed	standard deviation of speed was significant with a positive sign indicating that large variations increase the likelihood of severe crashes
9	Yu and Abdel-Aty (2014)	Standard deviation of speed	Large variation of speed is associated with severe outcomes
10	Choudhary et al. (2018)	Total flow Average Speed Between lanes speed variation Within lane speed variation	The within lane speed variance is associated with high rates of killed or seriously injured casualties. At high traffic flows, fatal and injury crash rates increase with increasing within lane speed variance. At high speeds, fatal and injury crash rates increase with increase in between lane speed variance
11	Zeng et al. (2019)	The percentage of vehicles in five vehicle classes	With a greater portion of light trucks, minivans, and minibusses, fatal and injury crashes are more likely to occur. A greater number of large trucks, buses, and trailers increase the chance of slight and severe injuries