A sea of motorbikes / scooters

Most people use motorbikes or scooters to move around Ho Chi Minh City. In a city of 8 million people, and most families have at least 2 bikes, that's an awful lot of bikes on the roads. Only the very well off have cars. On every street there are a few cars, a public bus or two, a handful of taxis and the motor bike brigade. It's Friday evening and I went out walking. The streets are just a seething mass of bikes. If you stand at an intersection and look down the road all you can see block after block is the whole road collectively filled with coloured bike helmets. The school transports us to and fro work in a bus so the view of the collective helmets is even more spectacular from a higher vantage point. From what I can gather the licence holder and driver of the bike must wear a helmet. Usually the pillion passenger wears a helmet too. Sadly children do not. You will often see a family of four on a bike. One child is often standing on the front scooter platform, and another sandwiched in between Mum and Dad.
On an environmental note: After walking for about 20 minutes you were aware of the impact on a personal level. My eyes began to get scratchy with particles in the air. After walking even longer you began to feel the grit on your skin. Many Vietnamese ride wearing nose and mouth masks and I can understand why. Conversely a family of 4 on a scooter uses much less fuel than a car, elevates the major parking problems and creates more road space for other bikes. parking your bike is interesting. You ride onto the footpath and park at a 90 degree angle against the shop footage, leaving only enough space to enter and exit through the shop door. This city really wouldn't cope if everyone drove cars as there is hardly enough footpath.
While the majority of people obey the road rules on their bikes many do not.
They often ride onto the footpath and around a corner to avoid waiting at the lights.
The white marker lines are only indicative, crowds may spill well into the oncoming lane. And you toot... move over, go faster, out of my way, I'm behind you, I'm turning behind you etc etc. So not only are the streets a seething mass of helmets they are a cacophony of horns.