In the run-up to parliamentary elections in Iran, Lara Petrossians of the BBC Persian Service sends a snapshot of an aspect of contemporary life in the Islamic Republic.
We're stuck in a traffic jam on a busy Tehran street. One driver decides enough is enough, and pulls out into the incoming traffic to overtake.
A car coming in the opposite direction screeches to a halt. Its driver jumps out, shouting insults, and a fist fight ensues.
Returning émigrés say they barely recognise Tehran
This is road rage, Tehran style, and it is symptomatic of a traffic problem that is getting out of control.
There are now around two million cars in Tehran. When you walk through the city you hardly ever see the traffic moving freely, even in the middle of the night.
Cars are stuck bumper to bumper. Drivers constantly sound their horns. Traffic policemen are such a rare sight that everyone breaks the rules of the road. Jumping a red light has become commonplace.
At the root of the problem is the way Tehran has grown since the revolution. In the past 20 years its population has doubled to 14 million people.
New roads and new housing developments have sprung up in a totally haphazard way. The city now extends far beyond its old limits, and émigrés returning home after many years say they barely recognise the place.
Attempts by the authorities to control the traffic have so far had little result. More than 300 kilometres of new roads have been built in the well-off northern part of the city. They curve through the new high-rise districts, but the traffic remains heavy.
Old, inefficient cars add to the problem
A system in place since 1980 requiring drivers to pay for access to the city on weekdays has failed to have any impact.
And then there is the long-awaited underground system. It has been up and running for more than three years now, carrying up to 600,000 passengers across the city every day.
Has it made a difference to the amount of traffic on the roads? Not really, say weary Tehran residents.
Tehran is one of the most polluted cities in the world. When you first arrive, you think there must be a huge fire somewhere.
You get a burning feeling in your eyes and throat. On most days there is a thick layer of dense smoke spread like a blanket over the city.
Pollution tends to hang over the mountain-surrounded city
When it passes the danger level, which happens quite a lot, schools are closed, and old people and those with heart problems are advised to stay at home.
It is estimated that up to 5,000 people die every year from air pollution in the city.
It is not just the number of vehicles on the road that is causing the problem. It is also the way they are made. Most of the cars in Tehran are locally produced Paykans - Iran's equivalent to the 1960s Hillman Hunter.
They are old, inefficient and most definitely do not use lead-free petrol. The situation is made even worse by geography. Tehran sits in a basin, surrounded by mountains, so that pollution tends to hang over the city until the wind blows.
The government has pledged to tackle the problem. New targets have been issued to phase out cars without catalytic converters, and to improve air quality levels.
Tehran is just one example but the same problem exists in big cities across the country. Officials are beginning to recognise that this is an issue of national concern.
When people talk about change in Iran, this is one of the things they mean. They do not just want a breath of freedom, they want a breath of fresh, clean air.