Earlier quoted context omitted.
$9 per day isn't going to make anybody change their route. A round trip on the subway costs $5.80. IMHO, they would need to push higher than $50 to get drivers to blink.
The thing about congestion is that reducing the number of drivers slightly (e.g. 10-20%) could eliminate congestion by 100%! This is the same way it works for electrical congestion. So you need pricing which will make a few people reconsider driving, who were on the edge of using public transit anyway.
Driving for a commute isn't really possible in Manhattan unless the company provides parking. And those parking spots are reserved for executives. This group of people are price insensitive.
Passing through Manhattan can frequently save an hour of time in traffic elsewhere, those commuters will just see the fee as a higher toll.
All three major airports never tied directly to a subway, opting instead for airtran systems which create complexity and cost time. I suspect this causes a base level of traffic.