Having music in a car isn't safety-critical. But we should have unflinching acceptance of reality that a lot of people WILL have music in the car, and so if mus

Having music in a car isn't safety-critical. But we should have unflinching acceptance of reality that a lot of people WILL have music in the car, and so if music adjustments are unsafe then the car is more unsafe. A while ago I worked on a military vehicle intercom system (communication between different station in tanks and armored vehicles). It had a number of pragmatic requirements, learned through experience. One of them was that each station had a 3.5mm jack that mixed its signal into what the headset was hearing. They had learned that whatever you did, soldiers were going to listen to music when they got bored. If you gave them a jack then at least they'd still have their headset on, and would hear instructions (and you could override the music if necessary...). Without the jack they'd just take their headset off. You have to accept the reality of the world you're designing for not the world you'd LIKE to be designing for. [Another pragmatic requirements anecdote from the same system: the comms bus had to be able to cope with random disconnects. Why? Because on a tank, the comms bus went to the commander in the turret via a contact ring and when the main gun fired, sometimes that contact ring would disconnect. But then we were allowed 1.5s to reconnect. That's a surprisingly long time - how come? Because that's how long it takes the tank commander's hearing to recover after firing!]