[SystemSafety] Small but useful Detail on Road Stopping Distances

Wed Jul 29 13:25:17 CEST 2015

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There was something in the local newspaper on Monday about the increasing accident rate amongst
motorcyclists in the state (North Rhine Westfalia). In Germany, troops of motorcyclists go out on
the weekend on fast machines to indulge in a spot of boy-racing, although they don't call it that.
A fair number of them come off on a curve and hit things. Then there are those who collide with
oncoming traffic during an overtaking manoeuvre, also often where sight is reduced, such as in
curves. Then there are those who just can't stop in time when something unexpected happens.

I have always liked motorcycles, have a licence and have owned a couple, but was always aware of
my vulnerability. I don't ride at the moment, because I prefer expending energy while travelling
(cycle) and don't like to have to cover myself up all over, especially my head, when it's nice
weather.

Accompanying the article was a neat statistic from the local police. They reckon stopping distance
from 30 kph is 9m reaction distance and 4,5m braking distance. From 50 kph it's 15m reaction
distance. So, they observe, someone travelling at 30 kph is already stopped before someone at 50
kph has reacted. Obviously there is variation involved which is omitted, but the principle in the
last sentence likely holds true per person and vehicle anyhow. Many people omit reaction time when
thinking about how they stop, or they have a completely unrealistic idea of the role it plays. The
speeds are chosen because they are two of the three speed restrictions inside urban areas. (The
third is "walking speed" on designated "play streets".)

PBL

Prof. Peter Bernard Ladkin, Faculty of Technology, University of Bielefeld, 33594 Bielefeld, Germany
Je suis Charlie
Tel+msg +49 (0)521 880 7319  www.rvs.uni-bielefeld.de