It's a cool Friday afternoon of around 20C. I am nearing home on my city cycle and stop at traffic lights but, as usual, not everyone wants to stop.

A scooter, liveried in shocking pink and white, follows a couple of other bikes into the opposite lane and rounding us all, crashes the red light and bullies its way into the deep stream of motorbikes swarming south. There are only two passengers on the seat behind the woman driver. They are also young women, with a haughty, sassy style.

They sit side-saddle, perfectly aware of how they look with their short skirts, right legs crossed over left and high heels hanging suspended in mid-air. For all the world they could be sitting on a park bench. One is checking her nails. The other is sweeping her waist-length hair over her shoulder.

The scooter forces its way into the centre of the traffic stream and we obedient citizens who stopped at the lights watch it crash, in slow motion, into another bike that swerved to avoid an SUV on the wrong side of the road.

Might is right on the streets of Phnom Penh. There's a metallic crashing sound, some bits of trim are torn off, and bike and scooter hit the road at slow speed. Three policemen, who have watched the whole thing, call the innocent rider over. They must have decided that they cannot make money out of this, as they impatiently wave him on. He picks up the bits of trim and weaves his way back into traffic.

The two women, scarcely batting an eyelid, have jumped nonchalantly off the scooter and stand in the middle of the traffic looking first at their driver, then at the other bikes swarming all around. Not a hair is out of place. They wiggle their rear ends as they pull down their skirts, and when the scooter is back to vertical, they sit on, cross legs in time, like synchronised swimmers, toss their heads back to settle their hair, and disappear in the traffic.

Everything you want to know about Cambodia's city society is found in the traffic of Phnom Penh – social conformity mixed with anarchic individualism, the confidence of young Cambodian women, the indifference of the police, the motorbike as an extra limb attached to the body, the inability of old cultural ways to cope with the modern world.

If I were a Cambodian policeman, I too would just stand and watch.