By John Simpson
World affairs editor, BBC News, Tehran
Tehran's traffic often suffers grid-lock, as does its politics
The traffic is worse than ever here.
Cars are the curse of Tehran, but they represent freedom for the millions of people who live here.
This is a huge, sprawling city, which has crept steadily northwards into the magnificent Alburz Mountains and southwards across the desert plain.
As one of the world's main oil producers, Iran has yet to grasp the full threat of global warming.
So every hour throughout the day is rush hour, and every intersection seems blocked.
I've been coming to Iran for 30 years, and have watched the gridlock grow worse and worse in the streets - and also in the country's politics.
Real power rests, not with president or parliament, but with unelected committees of religious leaders
For years, the reformists - who want both closer ties with the West and an end to the intrusive controls over people's lives - have battled it out with the conservatives who want to keep to the strict Islamic norms.
In the presidential elections of 1997 and 2001, the quiet, unexciting figure of Mohammed Khatami won enormous landslides, getting more than 80% of the vote on both occasions.
But in Iran, vox populi is not vox dei. Real power rests not with president or parliament, but with unelected committees of religious leaders who can and do veto any policy they dislike.
The conservatives also control large sections of the police as well as other organs of the Iranian state.
And when, back in 2001, my colleagues and I tried to film the public demonstrations in support of the newly re-elected President Khatami, we were attacked and arrested. One of the special policemen who assaulted us tried to poke my eye out with his finger.
In which other country would foreign television crews be beaten up for filming the celebrations when a new president has been elected?
It was a small example of Iran's political gridlock. And there were far more important examples to come.
Reformist, of sorts
President Khatami's second term in office produced very little in terms of new legislation, or opening to the outside world.
Mr Ahmadinejad was swept to power in 2005 largely by default
He could do almost nothing.
The presidential election of 2005 brought the extraordinary, unpredictable figure of Mahmoud Ahmadinejad to power, largely because few people wanted his opponent, Ali-Akbar Hashemi-Rafsanjani, back in power.
Mr Rafsanjani was a sort of reformist, but he had been deeply unpopular when he served as president before.
Mr Ahmadinejad swept in largely by default.
Ever since, the conservatives have been in the ascendant. And although the economy is shaky and inflation is disturbingly high, there seems to be little serious opposition to them.
And so many people who instinctively support the reformist cause will stay away from the polls.
Going round the vast, cavernous Grand Bazaar, which is as crowded with shoppers as the roads are crowded with cars, I came across people again and again who believed that voting in Friday's parliamentary elections was a waste of time.
Posters line Tehran's streets as the muted campaign gets under way
"This will just be a sham election," one young man said.
Even the reformist candidates I spoke to seemed gloomy about their chances.
"We will do our best, but you know..." said one woman.
So the conservatives are likely to do well, and President Ahmadinejad's power will be reinforced.
There are only a few countries in this region where the voters can change their government at the ballot-box.
Iran is far from being a full democracy, but it is a great deal more democratic than almost any country in the Arab world or Central Asia.
But if large numbers of people here decide that nothing will change if they vote, then voting becomes just a formality.
The political gridlock may have broken, but a new one will soon take its place.