They had a similar proposal for the Autobahns in Germany. The German automobile club came up with some interesting facts that you can add up:
1) Highways are safer to drive than secondary or city roads
2) Enacting a fee for highway use will make more people use secondary or city roads to avoid the fee
This brings up a few conclusions:
1) Deaths will go up do to increased usage of less safe roads
2) Congestion on the secondary roads will go up
3) If the alternate route goes through residential neighborhoods, pedestrian deaths are likely to go up
Wow! Women and minorities hardest hit!
In Germany the secondary roads follow routes laid down during the middle ages. Plus the gas tax is twice what it is in this country.