Imagine, if you will, a city with 5 single person households. This city has a roads budget of $1000/yr. Four of these households drive, the fifth does not.
Imagine, then, that the roads are funded similarly to how they are now: each household pays $100/yr in property tax, and the four driving households each pay $75/yr in gas tax, and $50 in a car registration fee.
The non-driver household pays $100/yr for roads, and each driving household pays $225. Is this a fair tax load given each household's use of the roads? Highly subjective, but it probably comes close. The non-driver does eat food shipped in on those roads, and uses the sidewalk and bike lane, but does not congest it with car traffic, which is as we know the primary cause of congestion in cities.
Now, Rob Ford comes onto the scene, abolishes the $50 car tax. Supposedly he's going to find $200/yr in "gravy" to offset this. Let's imagine he saves half of what he claims, as we know his estimates are grossly overestimated. New road budget is $900.
We're still collectiong $300/yr in gas taxes (4x75) but now each household faces a $20 levy on property taxes.
Non-driver pays $120, 20% more.
Drivers pay $195, $30 less, about 13%.
If "gravy" does not exist and you need to balance the full $1000, the levy is $40.
Non driver pays $140, 40% more
Drivers pay $215, 5% less.
This is why user fees such as the car tax are popular. They are naturally fairer. The driver sees relatively minimal savings offset by the non-drivers increase in costs, and because the latter group is much smaller their costs have to increase a lot to offset a small decrease in driver revenue.
Keep in mind that there is a very significant number of voluntary non-drivers, particularly downtown. Like I, who very much pays income and property tax.