When it brings you down to zero at a stoplight behind traffic, sometimes start by itself when traffic starts and sometimes make you hit the button or the pedal to get going again?

Is it a matter of how long you’ve been waiting or something?

 

That is correct. If you wait too long, you will need to step on the pedal again to restart.

 

I'm in agreement with LSFT. My opinion/assumption is that it's a safety feature. If you've come to a complete stop, you might start doing other things and not paying attention to the road, so Lexus errs on the side of caution and makes you reactivate motion by tapping the accelerator. Pros and cons, like many safety features.

 

I think they purposely did that so that you do not think it's a fully autonomous car. It's mentally reminding you that it's only an adaptive cruise control function. You still need to take control over the vehicle.