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

Table 1

Descriptive statistics of the variables included in the random parameters duration models.

Variables	Inside ASAP area (76.2%)		Outside ASAP area (23.8%)
	Mean	Standard deviation	Mean	Standard deviation
Dependent variable
Incident clearance time	47.823	38.447	74.131	55.197
Explanatory variables
Incident characteristics
Multiple vehicles involved in crash incident (1 if yes, 0 otherwise)	0.748	0.434	0.550	0.498
Commercial motor vehicle (CMV) involved (1 if yes, 0 otherwise)	0.066	0.248	0.097	0.296
Fatality involved (1 if yes, 0 otherwise)	0.005	0.069	0.032	0.177
Vehicle towed (1 if yes, 0 otherwise)	0.543	0.498	0.688	0.463
Seat belt indicated as involved (1 if yes, 0 otherwise)	0.815	0.388	0.848	0.359
On-road (1 if yes, 0 otherwise)	0.820	0.383	0.646	0.478
Overturn (1 if yes, 0 otherwise)	0.032	0.176	0.061	0.239
Collision type: rear end collision (1 if yes, 0 otherwise)	0.485	0.500	0.344	0.475
Temporal characteristics
Nighttime (lighting condition at time of crash incident: 1 if yes, 0 otherwise)	0.274	0.446	0.280	0.449
Winter (incident occurred in month of December, January, or February: 1 if yes, 0 otherwise)	0.261	0.439	0.183	0.386
Peak hours (1 if incident occurred between 7 AM–9 AM and 4 PM–6 PM, 0 otherwise)	0.488	0.500	0.373	0.484
Environmental characteristics
Rain (1 if yes, 0 otherwise)	0.156	0.363	0.173	0.378
Traffic characteristics
Average annual daily traffic (AADT/1000)	87.634	27.309	46.658	18.776
One lane in the traffic way	0.013	0.113	0.008	0.087
More than two lanes in the traffic way	0.911	0.285	0.920	0.271
Less than four lanes in the traffic way	0.208	0.406	0.095	0.293
Operational characteristics
Detection time (in minutes)	1.460	4.019	1.328	5.983
Response time (in minutes)	0.831	6.070	0.831	6.069
Police response present (1 if yes, 0 otherwise)	0.955	0.208	0.973	0.161
Fire response present (1 if yes, 0 otherwise)	0.326	0.469	0.283	0.451
Hazardous materials response present (1 if yes, 0 otherwise)	0.003	0.054	0.002	0.044