Time Headway (THW)¶

Description¶

The THW metric calculates the time until actor \(A_1\) reaches the position of a lead vehicle \(A_2\) [Jansson2005] [Junietz2018a].

\[\mathit{THW}(A_1,A_2,t) = \min \{ \tilde{t} \ge 0 \,\mid\, p_1(t+\tilde{t}) = p_2(t) \}\,.\]

Analogously to THW, one can define the Headway (HW) metric [Jansson2005] simply as the distance to a lead vehicle, i.e.

\[\mathit{HW}(A_1,A_2,t) = d(p_1(t),p_2(t))\,.\]

Properties¶

Run-time capability¶

Yes

Target values¶

The THW, and HW in one example, are used by regulatory bodies in several countries to express driving recommendations and as a threshold for fines [Junietz2018a].

Country	Recommended	Threshold for fines
Germany	1.8 s	0.9 s
Sweden	3 s	1 s
Austria	2 s	0.4 s

Subject type¶

Road vehicles (automated and human)

Scenario type¶

Car following scenarios

Inputs¶

Static/dynamic objects and their state (pose, shape, etc.) at time t

Output scale¶

\((0,\infty]\), time (s), ratio scale

Reliability¶

Medium, comparable to HW with additional consideration of velocity

Validity¶

Medium, comparable to HW with additional consideration of velocity

Sensitivity¶

High, indicated by its use in legislation [Junietz2018a], also considers velocity compared to HW

Specificity¶

Low, as comparable to HW, but additional consideration of velocity

Prediction model¶

Time window¶

Unbound, but usefulness depends on DMM

Time mode¶

Linear time