Generally the most important thing is not to get caught in the middle of a breeding herd with females and calves. Then you have your displaying bulls that parade up and down the road having "fun" intimidating vehicles, normally not dangerous but reversing and waiting is prudent. In fact, better safe than sorry is the motto!
You do get the
crazy "musth" bulls, but that is very rare indeed and there is not much you can do about that. They diagnostically have wet hind legs due to constant urine activity...the leaking temporal glands do not necessarily indicate a sign of danger.
A safe distance is to just be about 20 metres "past" the bull regarding the route, with your engine running, so that you can move along quickly should he charge or flap ears etc. A safe distance for breeding herds is 100m if possible, and it is important to stress that one checks the bush on both sides of the road upon arrival, that is the driver's job, and he/she should do that first, even if the elephants all appear to be across the road already. When in doubt reverse and watch.
Elephants are not stupid, and are very aware of their priorities. For example, at an ellie "roadblock", I have often welcomed even a small truck, passing the waiting vehicles and simply chasing the elephant/s away.
As Sprocky and Scips say, with experience, one may guage the temperament of the animal, and adjust accordingly. But once again, better safe than sorry!
The above is only my experience...hope it helps!
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