Hear me out….
Most departments have a fleet services or a division of equipment, something along those lines, but the main idea is that apparatus that need to be maintained. Maybe, just an idea, we get a building to service vehicles at certain points. Say every 4500-5500 miles, an apparatus needs an oil change and the game randomly chooses a mileage point within that area. Now your vehicle needs to go out of service and head over to fleet services, and the oil change takes maybe 2 hours.
You might think, “Why the heck would I want to have a building that takes away my resources for valuable hours”
To combat this, most departments also have a reserve fleet. As a player maybe you build a fire station just for reserve apparatus that are out of service until they need to get shifted to a station to cover a vehicles maintenance time.
Better yet, maybe the fleet services has reserve apparatus room where you can put however many units you need.
Maybe your ambulance breaks down and you need a fleet services utility to go and fix it, or a fleet services tow truck to bring it back to the shop? (New education: Tow Truck Operator??? Mechanic???)
The possibilities are endless!
Just some ideas, I think it would add realism and be a cool addition.