Evaluating the Impact of Freeway Service Patrol on Incident Clearance Times: A Spatial Transferability Test

Table 2

Random parameters hazard-based duration model results.

Variables	Combined		Inside ASAP area		Outside ASAP area
	Estimated parameter	t-statistic	Estimated parameter	t-statistic	Estimated parameter	t-statistic
Constant	4.167	64.07	3.843	51.42	4.302	29.11
Incident characteristics
Multiple vehicles involved in crash incident (1 if yes, 0 otherwise)	0.154	4.28	0.211	4.90
Commercial motor vehicle (CMV) involved (1 if yes, 0 otherwise)	0.397	8.70	0.437	8.20	0.413	4.43
Fatality involved (1 if yes, 0 otherwise)	0.818	7.52	1.106	5.06	0.617	4.41
Vehicle towed (1 if yes, 0 otherwise)	0.364	13.59	0.408	13.39	0.219	3.74
Seat belt indicated as involved (1 if yes, 0 otherwise)	−0.155	−5.00	−0.070	−1.96	−0.319	−4.54
On-road (1 if yes, 0 otherwise)	−0.190	−5.01	−0.247	−5.26	−0.090	−1.35
Standard deviation of normal distribution parameter	0.320	26.45	0.363	27.93	0.144	4.94
Overturn (1 if yes, 0 otherwise)			0.225	2.63
Collision type: rear end collision (1 if yes, 0 otherwise)					0.161	2.59
Temporal characteristics
Nighttime (lighting condition at time of crash incident: 1 if yes, 0 otherwise)	0.096	3.67	0.092	3.03	0.124	2.22
Standard deviation of normal distribution parameter	0.169	7.86	0.197	8.06	0.163	3.44
Winter (incident occurred in month of December, January, or February: 1 if yes, 0 otherwise)					0.194	3.05
Peak hours (1 if incident occurred between 7 AM–9 AM and 4 PM–6 PM, 0 otherwise)	−0.111	−4.65	−0.099	−3.68
Standard deviation of normal distribution parameter	0.127	7.72	0.124	6.78
Environmental characteristics
Rain (1 if yes, 0 otherwise)	0.070	2.23	0.077	2.09
Standard deviation of normal distribution parameter			0.270	8.27
Traffic characteristics
Average annual daily traffic (AADT)	−0.006	−14.33	−0.004	−8.44	−0.004	−2.27
Standard deviation of normal distribution parameter	0.002	14.26
One lane in the traffic way			−0.265	−2.07
More than two lanes in the traffic way					0.185	1.98
Less than four lanes in the traffic way	−0.110	−3.79
Operational characteristics
Detection time (in minutes)	0.007	2.60			0.016	4.34
Response time (in minutes)	0.009	3.80	0.011	3.99
Police response present (1 if yes, 0 otherwise)	0.139	3.16	0.153	3.27
Fire response present (1 if yes, 0 otherwise)	0.197	7.46	0.224	7.53	0.178	3.23
Standard deviation of normal distribution parameter			0.085	3.80	0.185	4.33
Hazardous materials response present (1 if yes, 0 otherwise)	1.043	4.58
Sigma (scale parameter)	0.531	63.71	0.529	55.60	0.532	31.37
Log-likelihood at convergence	−2426.087		−1866.010		−530.256
Number of observations	2206		1680		526