Hello Jakob,

Thanks for the clarification.

I went back to the output of both approaches to compare, and I was expecting to 
see that the minTTC value would change to a lower one when the one I calculate 
is equal to that value. But what I found are completely different values 
(example snippet in the attached csv file.)
am I calculating the ttc wrong?

Thanks
Mariam


From: sumo-user <sumo-user-boun...@eclipse.org> On Behalf Of Jakob Erdmann
Sent: Friday, May 13, 2022 1:48 AM
To: Sumo project User discussions <sumo-user@eclipse.org>
Subject: Re: [sumo-user] Calculating time-to-collision

minTTC returns the *minimum* TTC observed for all ongoing encounters of the ego 
vehicle (during the whole time of the encounter thus far) instead of the 
current TTC which you are calculating.

Am Fr., 13. Mai 2022 um 02:43 Uhr schrieb Mariam Wessam Hassan Mohamed Nour 
<mariam.n...@knights.ucf.edu<mailto:mariam.n...@knights.ucf.edu>>:
Hi all,

I'm trying to calculate time to collision at every time step for each vehicle 
in sumo.

I'm getting the spacing between each two vehicles as well as the speed of the 
leader using the getLeader function. Then I use the equation 
((spacing+minGap)/difference in speed) to get ttc.
The gap calculation was based on this 
(https://github.com/eclipse/sumo/issues/10178<https://nam02.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Feclipse%2Fsumo%2Fissues%2F10178&data=05%7C01%7Cmariam.nour%40knights.ucf.edu%7Cd13e51836af04bf16ab908da34a438cd%7C5b16e18278b3412c919668342689eeb7%7C0%7C1%7C637880177181658316%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=eXbbAPsj47mtscLkyZ3utWJRF%2BqHGgrDOdyfyWnOMIU%3D&reserved=0>)

On the other hand, every vehicle is equipped with an SSM device to calculate 
ttc. So I'm also able to directly get ttc values for each vehicle using 
traci.vehicle.getParameter(veh, "device.ssm.minTTC"). However, this ttc value 
and the one I calculate above don't match.

Am I calculating ttc using wrong values in the first approach? If not, then 
what could be the problem?

Thanks
Mariam

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Attachment: snippet_ttc.csv
Description: snippet_ttc.csv

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