It one can put two wheels on the walkway, and a wheel chair can pass, then the walkway is too wide.
The footpaths, down our street, are so narrow that those walking, walk either single file, or one on the road. Everyone either has a drive, or space for one. The drive space varies between one car, to the five, or even the seven which I have. Despite this limited space, the footpaths are regularly obstructed for days, by bins, or permanently by hedges growing across the path.
The road width, is wide enough, with care, for two lorries to pass each other. With a car parked, there is still room for cars, with care to pass each other, though most use common sense and slow down, or stop where there is a parked vehicle. So, absolutely no need for anyone to drive on, or park on the footpath. Just to repeat - those parking on the footpath, serve little or no purpose, for passing traffic.
Yet, most drivers see it as their absolute right, to park on the footpath, many completely blocking it. The worst offenders - the delivery guys, dropping off small parcels. I have no issue with large trucks, making heavy deliveries parking on the footpath, to keep pedestrians out of the risky area. Part of the reason, is that we have low kerbs, only an inch or two, with lots of dropped kerbs for drives.
We have a rail station close, and primary schools at either end - so at times, we get quite a few pedestrians trying to use the paths, kids, mothers with prams, disabled on scooters, and all being forced to find their way out on the road, to get past the odd vehicle parked obstructing the path. Many, rather than going constantly in and out, choose to just walk out on the road. The main line railway, which passes us, is being upgraded, so we often have rail replacement coaches up and down the street, every 30 minutes. Large coaches, mixing with people walking out on the road, seems extremely dodgy.