Table 2.

Overview of the feature variables used in this study.

Factor	Code	Variable	Description
Horizontal alignment	HPNE	Number of horizontal change points	The number of change points of horizontal alignment
	CULR	Curve length ratio	Ratio of curve length per kilometer (value between 0 and 1)
	STLR	Straight length ratio	Ratio of straight length per kilometer (value between 0 and 1)
	RIMX	Maximum curve radius index	Maximum value of the inverse of the radius. RIMX takes 0 in the straight sections
	RICU	Cumulative radius index	Cumulative value of the inverse of the radius
Vertical alignment	VPNE	Number of vertical change points	The number of change points of vertical alignment
	GAE	Average grade	Average grade per kilometer
	GMX	Maximum grade	Maximum grade per kilometer
	GDF	Grade difference	The difference in the maximum grade per kilometer
	DWLR	Downhill length ratio	The proportion of downhill in the section
Pavement	PCI	Pavement surface condition index	The value is between 0 and 100; the lower the value, the more serious the road damage.
	RQI	Riding quality index	The value is between 0 and 100; the lower the value, the lower the smoothness of the road surface.
	RDI	Rutting depth index	The value is between 0 and 100; the lower the value, the deeper the road rut.
	SRI	Skidding resistance index	The value is between 0 and 100; the lower the value, the lower the anti-skid performance of the pavement.
Tunnels and expressway facilities	TNN	Tunnel	0—No tunnel in the section; 1—There are tunnels in the section.
	ITC	Interchange	0—There is no interchange in the section; 1—There are interchanges in the section.
	SVA	Service area	0—There is no service area in the section; 1—There are service areas in the section.
Weather	WET	Weather	1—Sunny; 2—Cloudy; 3—Overcast; 4—Rainy.