Hello ,
You wouldn't be able to do this with a vehicle path, since every vehicle on a path can only move at a specified speed. You can accomplish this with Twinmotion's animation tools (translators and rotators). Twinmotion's animator tools aren't designed for very complex animations, so it will require some clever editing and will have a fair amount of limitations.
You will want to use a translator to have the vehicle move and stop at the stop sign, and create a video clip of this.
Since only a single animator could be applied to an object, and since animators don't support start and stop functionality, you will want to create a separate scene state with an identical vehicle placed at the stop sign exactly where the first vehicle stops, with the first vehicle hidden. In a separate video part, set the scene state to the newly created scene state with the new vehicle. You can then apply a translator to the new vehicle and set this to a delay of however many seconds you need the vehicle to stay stopped, so that the vehicle only moves after waiting a bit. When played back-to-back, the two video clips can give the impression that the vehicle stops at the stop sign before driving off.
This isn't an ideal solution if you want to show the vehicle's wheels moving, since Twinmotion's native library vehicles don't have dynamic wheels and will remain motionless during the animation.
Best,
Raghib