You can indirectly control such lane changes by giving your emergency vehicles a higher speed than normal traffic. However, this will not work 100% as some cars might not be able to move over in time.
Alternatively, have a separate road (visually right next to the normal road). Add lots of transitions to the normal road. Under normal conditions, cars use it like the normal road.
However, once an emergency arrives, make all cars leave that road and keep it clear for emergency vehicles.
In other words: use a road like a custom lane.
Not elegant, fair bit of manual work... but it works
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