Research Article
Development of Accident Frequency Models with Random Parameters on Interstate Roadway Segments with and without Lighting Systems
Table 1
Descriptive statistics of variables.
| | Variable description | Segments with lighting system | Segments without lighting system | | Mean | Std. Dev. | Min. value | Max. value | Mean | Std. Dev. | Min. value | Max. value |
| | Segment length (miles) | 1.22 | 1.78 | 0.03 | 14.16 | 2.09 | 2.51 | 0.01 | 20.38 | | Number of accidents per year | 13.63 | 16.55 | 0.00 | 128.00 | 8.67 | 11.34 | 0.00 | 123.00 | | Portion of segments without lighting system | 0.00 | 0.00 | 0.00 | 0.00 | 1.00 | 0.00 | 1.00 | 1.00 | | Average daily traffic volume | 17,821 | 8,946 | 993 | 44,223 | 10,569 | 6,958 | 916 | 35,948 | | Proportion of segments with standard number of lanes | 0.01 | 0.10 | 0.00 | 1.00 | 0.00 | 0.00 | 0.00 | 1.00 | | Proportion of segments with low number of lanes | 0.98 | 0.16 | 0.00 | 1.00 | 0.99 | 0.13 | 0.00 | 1.00 | | Proportion of segments with low left shoulder width | 0.25 | 0.45 | 0.00 | 1.00 | 0.29 | 0.44 | 0.00 | 1.00 | | Proportion of segments with standard left shoulder width | 0.67 | 0.96 | 0.00 | 1.00 | 0.67 | 0.97 | 0.00 | 1.00 | | Proportion of segments with high left shoulder width | 0.08 | 0.49 | 0.00 | 1.00 | 0.04 | 0.29 | 0.00 | 1.00 | | Proportion of segments with low right shoulder width | 0.34 | 0.43 | 0.00 | 1.00 | 0.25 | 0.43 | 0.00 | 1.00 | | Proportion of segments with standard right shoulder width | 0.59 | 0.93 | 0.00 | 1.00 | 0.70 | 0.96 | 0.00 | 1.00 | | Proportion of segments with high right shoulder width | 0.07 | 0.42 | 0.00 | 1.00 | 0.05 | 0.45 | 0.00 | 1.00 | | Number of horizontal curves in segment | 1.80 | 1.92 | 0.00 | 14.00 | 2.41 | 3.65 | 0.00 | 37.00 | | Number of vertical curves in segment | 2.92 | 3.17 | 0.00 | 17.00 | 4.40 | 4.35 | 0.00 | 30.00 |
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