Interesting - that must be country specific!
I agree with respect to minimising gear changes but there is also a strong
incentive to conserve momentum, ie avoid braking, that will compromise the
'safe' distance?
In the UK at least the concept of trucks driving even a truck length apart is
subjectively rare and at busy times multiple trucks driving ~4-5m apart are
common, especially where the lead vehicle has not reached 60mph.
(In the UK trucks are limited to 60mph/97kph, these speeds usually being
exceeded on downhill stretches. )
Any UK car driver will have experience of a truck driving ridiculously close
behind them - far less safe given the relative stopping distances.
Cheers
Div
-------- Original Message --------
On 7 Sep 2021, 11:45, François Vaudrin wrote:
> 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]>:
>
>> 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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