I was reminded of a fairly recent Aussie incident report in which a Saab 340 was doing 26 knots (= 30mph) when a Dash-8 had to do a sudden stop from 21 knots (= 24mph) to avoid a collision. You can see from the SYD airfield chart that this wasn't in some out of the way part of field but very close to the domestic terminals - so these are pretty normal taxi speeds.

I remember a taxi journey in London when the cab had to stop suddenly from that sort of speed and I wasn't wearing a seatbelt. Even though I could see it coming, I ended up on the floor - although fortunately not hurt.