I don't think it's quite correct to call it a regressive tax. Driving a car in Manhattan is a luxury, so this is a tax on a luxury that subsidizes transportation that works for everyone.
Taxes on luxury goods typically aren't expected to significantly reduce their consumption, because they're purchased by price-insensitive wealthy people. But the congestion pricing seems to be deterring use, and indeed is explicitly intended to, so who are these price-sensitive people being subject to the tax?