I am not for or against a traffic fee at this moment but I do realize a few things:
Traffic is a problem that isn't going away and it will cost lots of money to improve even by a small amount.
The cost has to be paid by some means. (Gas tax, tolls, blanket taxes, other specific fees)
The fairest thing is to charge those who are contributing to it (people who are on the road.)
It is easy to complain about the cost involved and I notice everyone complains about a price increase regardless of whether it is warranted or not.
I do suspect that this idea is part of the plan to incentivize the future rail travel. The more being on the road costs, the more people will look for ways to avoid traffic (bus, rail, bicycle, etc)
I think there may be a few ways that the city could lighten traffic marginally without significant cost. One of them I want to get behind is to have government workers on a 4 day, 10 hour, schedule. This would spread congestion to a wider time frame and would see government employees spend 20% less time in traffic. It would also save them gas money.