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