about video a couple posts above

anything you say or do, even pulling to the side or getting out of your car, is voluntary that simple

staying there longer than 20 minutes is no longer detainment and it becomes a voluntary action or arrest.
if you are under arrest the officer must state so clearly and a valid reason for the arrest or it is an unlawful arrest and you are free to go

also that big white truck is mounted with a side scan x-ray device that is why they ask you to pull over to the side next to it

FYI interstate land is owned by the Federal Govt not State just so you know legally where you are when traveling the interstates.