Danke Jakob,

It's perfect, I'll think about what I can do with the "tau".


If it can help for future improvement of SUMO, here's some additional 
information that I received:


- The braking distance is different if the truck is full or empty.

- The delay for the truck to start braking would be approximately 3 seconds for 
a semi-trailer: 1 second for the reaction time + 2 seconds for the mechanical 
delay to reach the rear of the truck (to apply the brakes).

- Truckers try as much as possible to keep a constant speed to avoid frequent 
gear changes and they try to keep a gap in order to avoid frequent stops and 
departures.


Best

François

________________________________
De : sumo-user <[email protected]> de la part de Jakob Erdmann 
<[email protected]>
Envoyé : mardi 7 septembre 2021 02:13
À : Sumo project User discussions <[email protected]>
Objet : Re: [sumo-user] Safe distance for a trucker (headway)

I'd guess that in this rule of thumb, truck length is a proxy for weight and 
hence deceleration capability.
Since the relationship between decel, speed and headway isn't linear in speed, 
you'll find it easier to reproduce the linear rule-of-thumb gaps with different 
values of tau for different lengths of truck.
Though, when following the physics, modeling it with different values of decel 
for different sizes of truck should be a better fit for reality.
Per my understanding the trucker rule is just an easy-to-calculate 
approximation for the physics.

Am Di., 7. Sept. 2021 um 01:27 Uhr schrieb François Vaudrin 
<[email protected]<mailto:[email protected]>>:

Hello,


It seems the rule for truckers is to keep a safe distance of one truck length 
per 10 km/h. So, if a truck driver is traveling at 100 km/h and his truck is 20 
m long, he should keep a distance of 200 m from the vehicle in front of him.


I thought to use the "tau" parameter, but it is related to reaction time as I 
understand and it does not seem to take into account the length of the truck.



Thank you,


François Vaudrin, PhD
 CANADA
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