Safety Evaluation for Highway Geometric Design Based on Spatial Path Properties

Table 1

Combination of horizontal and vertical alignments.

Spatial position	Vertical alignment	Shape description
Horizontal alignment	Tangent & ^†tangent	Spatial straight line
	Tangent & parabola	Crest or sag curve
	Euler spiral & tangent	Conical helix
	Euler spiral & parabola	Conical helix
	Circular curve & tangent	Cylindrical helix
	Circular curve & parabola	Cylindrical helix

Note. Sign & ^†denotes superposition of two line elements.