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Re: [sumo-user] Secure gap, brake gap and stopping distance

> Is there a difference between secure gap, brake gap and stopping distance (from kinematics)?

- brakeGap: for a given speed, the distance until stopping when braking with constant deceleration 'decel'
- stopping distance: same as above for Krauss. Some cfModels take longer to stop since they do not brake with constant deceleration.
- secure gap: the distance that allows safe braking if the leader vehicle suddenly starts to brake. Roughly speaking, the following holds: egoSpeed * tau + egoBrakeGap = secureGap + leaderBrakeGap. 
  Depends strongly on leaderSpeed

For details on the code, see MSCFModel.h and .cpp

SecureGap has no meaning if there is no leader vehicle

Decel is the preferred/comfortable maximum deceleration used in motion planning. emergencyDecel is the upper limit on deceleration in emergency situations


Am Fr., 8. Apr. 2022 um 15:45 Uhr schrieb Hriday Sanghvi via sumo-user <sumo-user@xxxxxxxxxxx>:

Is there a difference between secure gap, brake gap and stopping distance (from kinematics)?

As far as I understand, the secure gap / brake gap / stopping distance calculation does not depend on the CF model, since this calculation is the same for all CF models. My CF model is Krauss.

1. My assumption was that the secure gap and brake gap are the same. But when I check on "show brake gap" in the SUMO-GUI, and display the "secureGap" using traci.getSecureGap(self, vehID, speed, leaderSpeed, leaderMaxDecel, leaderID=''), the values do not seem to reflect what happens in the GUI - for example, when TraCI outputs a secureGap of 0.0 - there is still a line sized bigger than 0.0 shown in the GUI.
- What would I set as the leader speed if there is no leader in front of it - the max speed on the lane (13.89 m/s)?

2. If I assume that the secure gap and brake gap are the same as the stopping distance used in kinematic physics, then does it just use those equations to calculate this stopping distance value? That is, using (Final velocity)^2 - (Initial velocity)^2 = 2 * acceleration * Distance to calculate the Distance for a constant acceleration / deceleration?

3. On a side note, what is the significance of emergencyDecel variable used in SUMO - to put it differently, why is just one deceleration capability value not enough? - since I couldn't find an equivalent to that in real-world driving.

Thank you.

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