Re: [SystemSafety] Small but useful Detail on Road Stopping Distances

From: Peter Bernard Ladkin < >
Date: Fri, 31 Jul 2015 08:47:15 +0200

Hash: SHA256

On 2015-07-30 08:18 , David Haworth wrote:
> On 2015-07-29 15:58:35 +0200, Peter Bernard Ladkin wrote:

>> The traffic law in Germany stipulates a reaction time of 1 second.

> The "halber Tacho"* rule for driving on the Autobahn approximates to a 2 second reaction time
> (since your safe distance behind another car doing the same speed is just your reaction time,
> all other things being equal). Or one second plus "engineering tolerance" ;-)

2 seconds is a decent enough estimate, but it's not what the law generally uses.

There is a ruling from the Supreme Court (Bundesgerichtshof) that the reaction time, including brake activation time, is about one second for unexpected events ("Bei einem unvermuteten Vorgang beträgt die Reaktions- und Bremsanprechzeit eine "knappe" Sekunde, s BGH NJW 00 3039, Ha VR 80 685" Hentschel, Strassenverkehrsrecht (Road traffic law), 37. Auflage (edition), note 30 to StVO §1). The law does recognise, though, that reaction times are variable (op. cit.)

Jagow Burmann Hess, Strassenverkersrecht (Road traffic law) has a diagram in the commentary to StVO §3, note 13, which gives a diagram for stopping distances at various speeds, in which the reaction distance is based upon a reaction time of 1 second. Source is given as the Verkehrswacht Dortmund.

Here is a non-authoritative Internet source which also uses 1 sec: and says "Bei diesen Faustformeln wird eine Reaktionszeit von 1 Sekunde angenommen" ("In this rule of thumb, a reaction time of 1 second is used")

And here is that of course supreme authority Wikipedia "Die Reaktionszeit beträgt typischerweise eine Sekunde" ("Reaction time is typically 1 second")

And here is the Polizeipräsidium in Frankfurt am Main also saying "on average 1 second" (second page bottom)

Here is the calculation taught at the Police Academy in Brandenburg by Kammann and Lederer

The roadway engineering texts are a little less rigid.

The roadway engineering textbook Mensebach, Strassenverkehrsplanung /Strassenverkehrstechnik, (Road traffic planning and technology) 4. Auflage, Werner Verlag 2004, Section 2.1.2 Bremsvorgang (the braking process) says the reaction time is 0,6 to 1,8 seconds, average 1 second.

The roadway engineering textbook Schnabel/Lohse, Grundlagen der Strassenverkehrstechnik und der Verkehrplanung Band 1, 2. Auflage (Fundamentals of road traffic technology and traffic planning, Volume 1, 2nd edition) says (p51) that the reaction time lies between 0.5 and 1.5 seconds, and that the activation time for the brakes is a further 0.2 to 0.3 seconds and is often counted in as "reaction time", so that gives 0.7-1.7 seconds or 0.8-1.8 seconds depending on which you take.

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

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systemsafety_at_xxxxxx Received on Fri Jul 31 2015 - 08:47:25 CEST

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