Yeah but a toll doesn't accurately reflect the amount of damage done to a road. A light econobox will do just about no damage to a road whereas a huge F350 with a curb weight of over 3 tons is going to do a great deal more damage even though it might only weigh twice as much. Adding to this, a large truck is going to make passenger vehicles look like a rounding error. Tolls could be made to reflect the estimated additional wear and tear on the road but effectively this would mean that passenger cars just pay a toll for the initial construction costs of the road and large vehicles pay the same plus an additional charge to cover all of the wear to a road.
That PDF is one of the worse documents of any kind that I have seen. Given that you're just giving general info about road wear, you could probably have simply stated that road wear is typically proportional to the fourth power of axle load. A cursory internet search pulled up the following document which seems to give a good overview of the topic:
http://facweb.knowlton.ohio-state.edu/pviton/courses2/crp776...