An Investigation of the Safety Performance of Roundabouts in Korea Based on a Random Parameters Count Model

Table 4

Descriptive statistics of the variables.

Variable Description	Mean	Standard Deviation	Min.	Max
Region (urban: 1; rural: 0)	0.683	0.466	0	1
3-legged roundabout	0.357	0.480	0	1
4-legged roundabout	0.513	0.501	0	1
5-legged roundabout	0.131	0.338	0	1
Average radius of the entry lane (m)	20.872	12.121	5.5	98.75
Lane number of the entry/exit lane	1.170	0.395	1	3.2
Average lane width of the entry lane (m)	4.319	1.022	3	10.9
Average lane width of the exit lane (m)	4.556	1.068	2	10.1
Pedestrian crosswalk (yes: 1; otherwise: 0)	0.769	0.423	0	1
Distance between the stop line and pedestrian crosswalk	9.26	6.62	0	21
Central island (yes: 1; otherwise: 0)	0.950	0.219	0	1
Vertical grade (yes: 1; otherwise: 0)	0.412	0.493	0	1
Exclusive right turn lane (yes: 1; otherwise: 0)	0.231	0.423	0	1
Number of accidents per year	2.553	4.384	0	37
Logarithm of AADT	9.123	8.852	4.60	10.54
Diameter of the roundabout (m)	31.148	8.335	9	80
Diameter of the central island (m)	17.380	6.150	3	40
Number of circulatory lanes in the roundabout	1.116	0.336	1	3
Width of the circulatory lanes in roundabouts (m)	5.151	0.564	3.8	7