Yes I drive, every day
other than rush hour traffic has been moving completely freely around cardiff every time I've been out and about, the only traffic problems I've encountered during rush hour have been on roads that aren't affected by the change to 20 mph (A470 predominately).
If "oldies are sitting in nappies for hours" that probably has a lot more to do with the chronic shortage of carers in the system rather than that some of their journey is a little bit slower.