Steady-State Car-Following Time Gaps: An Empirical Study Using Naturalistic Driving Data

Table 4

Best statistical distributions for all drivers and all speed intervals according to the K-S goodness-of-fit method.

Speed Interval	Distribution	Parameters	pdf
	Johnson	Shape parameters: γ = -0.574/ δ = 0.756
		Scale parameter: λ = 1.137
		Location parameter: ξ = 1.799	where
	Johnson	Shape parameters: γ = -0.655/ δ = 1.095
		Scale parameter: λ = 2.723
		Location parameter: ξ = 0.757	where
	Pearson 6	Shape parameters: α1 = 899.2/α2 = 478.4
		Scale parameter: β = 5.119
		Location parameter: γ = -7.574
			where B is the Beta function
	Pert	Mode parameter: m = 1.47
		Lower boundary parameter: a = 0.57
		Upper boundary parameter: b = 3.867	where
	Kumaraswamy	Shape parameters: α1 = 1.739/α2 = 249
		Lower boundary parameter: a = 0.46
		Upper boundary parameter: b = 25.5	where
	Pearson 5	Shape parameter: α = 7.75
		Scale parameter: β = 8.78
		Location parameter: γ = 0	where Γ is the gamma function
≥ 108	Kumaraswamy	Shape parameters: α1 = 1.728/α2 = 5.604
		Lower boundary parameter: a = 0.31
		Upper boundary parameter: b = 3.76	where