Without going to dynamic pricing, there could be timed pricing for busier times. E.g.
$3 - 7-9 am , 4-6 pm weekdays
$2 - 6-7 am, 9-10 am, 3-4 pm, 6-7 pm weekdays
$1  - 10 am - 3 pm weekedays
free otherwise

Also, this could be combined with a vehicle registration tax, which allow locals either a discount or a certain amount of free travel on the highways.