Who said anything about speed? A vehicle like a fire truck can simply be too long/wide to get around a corner even at a walking pace. So they use the sidewalks. Emergency vehicles in pedestrian areas is a very common. So any barrier system needs to accommodate them.
Every, and I mean every, neighborhood is laid out on the premise that firetrucks can get to every location. The size of buildings, even the width of city blocks, is often tied to the capacities of the local fire departments to push water using pumper trucks. Want multi-story residential areas? The roads better be able to handle ladder trucks too.
It’s possible to reduce the size of the fire trucks, too. Not every ladder truck needs to be a full double-steered classic hook and ladder; modern extension trucks can be relatively compact.
Amusingly enough around here the widest streets are the oldest; because they were wide enough to turn a wagon and a team of horses. Some of the newest streets are quite narrow - a truck can go down them easily enough but turning around would involve a driveway.
Every, and I mean every, neighborhood is laid out on the premise that firetrucks can get to every location. The size of buildings, even the width of city blocks, is often tied to the capacities of the local fire departments to push water using pumper trucks. Want multi-story residential areas? The roads better be able to handle ladder trucks too.