Quantification of Rear-End Crash Risk and Analysis of Its Influencing Factors Based on a New Surrogate Safety Measure

Table 6

Estimated parameters of the the mixed-effects linear regression model.

Explanatory variables			Std. Err.	Z	P>|Z|	95% CI
						Lower	Upper
Fixed effects (behavioral variables)
Duration of car-following event		−9.52e − 07	1.29e − 07	−7.36	<0.001	−1.20e − 06	−6.98e − 07
Mean time headway		−0.00200	0.00003	−65.32	<0.001	−0.00206	−0.00194
Average speed difference		0.00029	8.18e − 06	35.07	<0.001	0.00027	0.00030
Acceleration difference ratio		0.00099	0.00005	18.80	<0.001	0.00088	0.00109
Fixed effects (temporal variables)
Day-of-week	Holiday (baseline)	—	—	—	—	—	—
	Workday	0.00022	0.00005	4.88	<0.001	0. 00013	0.00031
Time-of-day	Off peak (baseline)	—	—	—	—	—	—
	Morning peak	0.00010	0.00005	1.91	0.056	2.57e − 06	0.00020
	Evening peak	−0.00012	0.00005	−2.42	0.016	−0.00023	−0.00002
Fixed effects (environmental variables)
Light condition	Daytime (baseline)	—	—	—	—	—	—
	Nighttime	—	—	—	—	—	—
Weather condition	Sunny (baseline)	—	—	—	—	—	—
	Rainy	0.00013	0.00006	2.30	0.021	0.00002	0.00023
Traffic density	High (baseline)	—	—	—	—	—	—
	Median	−0.00203	0.00007	−27.10	<0.001	−0.00217	−0.00188
	Low	−0.00542	0.00007	−73.05	<0.001	−0.00557	−0.00527
Fixed effects (intercept)		0.00915	0.00016	58.55	<0.001	0.00884	0.00946
Random effects (group name: driver)
		Estimate	Std. Err.		95% conf. interval
Variance of intercept		5.53e − 07	1.05e − 07		3.81e − 07	8.01e − 07
Variance of residual		5.69e − 06	6.21e − 08		5.57e − 06	5.82e − 06
, Prob
Log likelihood		77997.65
LR test vs. linear model		, Prob
Number of observations		16,905
Number of groups		58