Add a yellow light for when there are stalls available but all free stalls have recently been used for more than 2 minutes.
So basically, yellow would mean "You could, but unless you really need to, you probably don't want to" ;)
So basically, yellow would mean "You could, but unless you really need to, you probably don't want to" ;)
You could make it very simple timer that holds the stall for a brief minute or two.