1. It's the closest thing to a "user fee" that governments have. It generates revenue from the road users, and gives a highway authority a source of money that doesn't have to compete with other spending from general tax revenues.
2. It gives the highway authority a lot of flexibility to run their system like a responsible private business owner would -- through things like variable tolling, discounts for electronic tolling, etc.
3. It allows the highway authority to have its own bonding capacity and its own bond rating, separate from a fiscally irresponsible government.
4. It gives a state or municipal government a mechanism for collecting revenue from people and businesses outside its jurisdiction who use its infrastructure and services. This is an important consideration for small states with a lot of long-distance traffic passing through it.
Personally, I think toll roads are going to become more common -- but they are also going to offer more benefits to their users. Ohio, for example, is looking at ways to make the Ohio Turnpike more attractive to motorists and truckers -- by potentially allowing higher speed limits, heavier weight limits, or a combination of both.
> It gives a state or municipal government a mechanism for collecting revenue from people and businesses outside its jurisdiction who use its infrastructure and services. This is an important consideration for small states with a lot of long-distance traffic passing through it.
Interstates should not be tolled.