Anecdotally, regenerative braking on an EV reduces brake pad wear by somewhere around 50-80%. It's rare to have to replace brake pads in an EV, or even to see them significantly worn.
On urban buses, which are constantly starting and stopping, I imagine it could be even more.
If EV companies were confident in their engineering, one could design a system with entirely electric braking.
No brake pads required. Simply dump the energy into the battery (or a big heater for the excess when the battery is full or too cold to charge)
Obviously, you can't have a failure in the electrical or control system or you can't brake anymore, so that part will have to be designed with much more redundancy than it is in todays vehicles.
"In urban environments, brake wear can contribute up to 55 % by mass to total non-exhaust traffic-related PM10 emissions" [1]. (The "abrasion processes which result in direct particulate matter (PM) emission are tyre, brake, clutch and road surface wear, with other potential sources being engine wear, abrasion of wheel bearings and corrosion of other vehicle components, street furniture and crash barriers.")
When a vehicle regeneratively brakes, the brakes aren't engaged. Instead, the transmission connects to a generator, which resists the vehicle's motion as it converts kinetic energy into electricity.
Braking dust comes from brake pads rubbing against brake disks. Electric vehicles slow down by running the motor in reverse and recharging the battery, therefore don't use the brake pads and brake disks as much, especially at higher speeds where the brake dust problem is the worst.
Regenerative braking is using the electric motor as a generator for a time during braking. So you're not dealing with pads and rotors wearing down, at least not as much.
On urban buses, which are constantly starting and stopping, I imagine it could be even more.