How to stop ALL incoming calls despite connecting to Bluetooth using Do Not Disturb while driving?

All iOS is most up to date - iOS 11.2.6

iPhone 6s

using Apple Map when driving.

The fact is - i just really need to stop all incoming calls whichever urgency it is when driving and i risk assess that the risk of accidents definitely outweighs that of taking an urgent call or whatever. Unfortunately it was thought that the iPhone would be smart enough to notice that connecting to Bluetooth would mean being safe to take calls (but the thing is Siri is pretty bad in the car and would affect me using the Map on the road!). I don't even drive a call with inbuilt Bluetooth system - i only use one of those little Bluetooth enabled audio device so that i can listen to music from my iPhone music library in the car.

So my question is simple - how do we stop ALL incoming calls, WhatsApp calls, WeChat calls, Line calls, etc etc when driving?

Many thanks in advance.