Suicidal. That is traffic in Indonesia in one word. Why? Imagine a large Italian city at rush hour with the large number of motorbikes: multiply it by 10, take the amount of cars (and buses and trucks) on a 3 lane highway each direction, but reduce the number of lanes to 1 each direction to get an idea about the number of vehicles. Of course you should not forget about occasional bikers and motorickshaws (called becak) either. Nevertheless the motorbikes and bicycles here are not of the normal size as they are loaded either with people (up to five) or cargo, including live animals in cages, full sized doors, harvested products piled up in the back, large screen TV sets, construction material, several meters long bamboo or sugar cane sticks, making one bike the size of a small car.
Then take away all traffic rules including do not take over from the right (in right hand traffic) or from both sides at the same time, use your rear view mirror before turning/taking over, stopping at red light or pedestrian crossings, not crossing at do not cross signs, do not enter a one way street from the wrong end, yielding, not driving on the side walk or in the opposite lane against traffic, wait for your turn in a traffic jam and do not start to take over the line of vehicles by crossing into the opposite lane and then blocking the traffic there, do not ride the motorbikes in the middle of the road or next to 2-3 other bikers in the same speed... and the list goes on and on until there are no traffic rules. They were all replaced by honking. You want to take over: honk and honk even more if there are some bikers in the opposite lane (after all they can also ride off road). There are 4 bikers in front of you riding parallel to each other: honk. There is a vehicle coming opposite in your lane: honk. There is a suicidal pedestrian, desperate to cross the road: honk. It has to be added that in spite of the constant use (actually surely because of it) honking is ineffective and the bikers will still be riding 4 in a parallel row, the vehicle coming against you will not break and stop taking over the other vehicle. It rather seems that honking is to signal your presence and let the others know you are coming and let them react to it without you having to slow down. That of course will make all traffic rules unnecessary: you just have to honk if you cross on red or take over under any circumstances.
Actually there might be one rule: “be faster!”, as the whole traffic resembles a car and motorbike race combined with showing off with your slaloming skills. The bus and truck drives might still have some sentimental feelings for their good old times when they were still riding a motorbike and think that the vehicle they are now driving is also as small and fit into the gap between two cars and is as good in slaloming between cars when e.g. they stop at the red light. This kind of driving can miraculously turn a 2 lane road to a 6 or 10 lane road: 1 or two lines of motorbikers on the side of the road, 1 car or truck and on other one taking it over with a motorbiker taking over the second car. And of course the same amount of vehicles driving the opposite direction, plus minus an occasional cyclist or becak on the shoulder of the road and the guy driving against the traffic there.
We have traveled around the world, but the traffic has not been that shocking anywhere. I was sitting in the buses in complete panic, constantly thinking that this is it, there is no way we will survive this ride. I still do not know how we did.