Table 4: Assessment criteria for potential crash hotspots on G109, Beijing.

CategoriesIndexesUnitsClass 2Class 3

Sharp curveThe horizontal curve radiusm ≤ 125 ≤ 60
Heavy gradientThe longitudinal gradient% ≥ 6.0 ≥ 7.0
Continuous downgradeThe longitudinal gradient% ≥ 4.5 (≥3 km) ≥ 5 (≥3 km)
Bad sight distanceDecision sight distancem ≤ 150 ≤ 80
Bad clear zoneThe height of slope m ≥ 4.0
The distance to shoulder border ≤ 3.0 (Lakes, rivers, swamps, ditches)