Trying to get around the Iranian capital by car is hard work.
Even outside rush hour, an estimated 20-minute trip in Tehran can easily turn into a two-hour nightmare.
By Europe Correspondent Paul Cunningham
The city's metro is modern, efficient and expanding, but because we need to carry lots of gear, TV crews tend to be car-dependent.
So, cameraman Pol Reygaerts and I would find ourselves as prisoners inside an old Peugeot 405, on a four-lane highway, going nowhere.
To lighten the mood we'd listen to music.
It was in a particularly grim traffic-jam that I first heard the sounds of '25Band'. Their hit - Ye Bade Khonak - soon became the favourite soundtrack to our day.
However, try to buy it in a music shop in Tehran and you'll be disappointed.
In Iran, it is the government - not you - who decides what is good music and what is bad. And '25 Band' is thought by the censors to be too racy.
Consequently, their videos are not shown on Iranian TV; their songs are not played on the airwaves; and their CDs are not allowed to be sold in shops.
'25Band' is a 6-piece Persian outfit now based in Dubai.
Their music is a cross-over of pop and hip-hop - it's contemporary and catchy.
'Ye Bade Khonak' means 'A Cool Breeze'. Vocalist Tamin sings with a startlingly beautiful voice.
People in Iran want to listen to '25Band'. So they get around the rules by downloading tracks to their phones and laptops from popular download sites such as radiojavan.com.
It seems there is little the censors can do about it.
It is the same with social media. Officially, Facebook and Twitter are banned.
Try to log-on in Iran and the censor's e-filter will prevent you.
So young Iranians simply download different browsers, such as Puffin, and then can tweet and post to their hearts content.
The ban on Twitter already looks ridiculous as the Iranian Foreign Minister, Mohammad Javad Zarif, has an account: @JZarif. So does the President @Rohani_hassan
If they can have accounts - why can't everyone else? How can students, for example, be arrested for trying to set up a Facebook page, when Minister Zarif is a paid-up member of the Twitterati?
There seems to be an unwritten rule: it's okay to have an account, just as long as it isn't used for political purposes to agitate against the government.
Since 1979, when Ayatollah Khomeini's revolution founded an Islamic state, the government controls all traditional media, can ban public meetings and can incarcerate dissidents.
However, Iranians in-the-know can now access whatever they want to on the web.
They can share what they want to share.
That powerful freedom delivered by the Digital Revolution poses a challenge to the Iranian Islamic Revolution.
The election last year of President Rohani reflected, in part, a desire by young people to have more control over their personal lives.
There is also a desire to look beyond the country's borders. Access to the net is increasing the exposure of Iranians to the English-speaking world.
English is now viewed as a passport to a better job.
Students are vying with each other to get access to third-level places in countries such as the US, Canada and the UK.
Set against that background, the old slogans like 'Down with the USA', painted on walls in Tehran, lose their power.
That is not to overstate things. Iran remains a tightly controlled society.
Police stopped us several times a day while we were filming on the streets.
Mostly they were courteous, but the regularity with which we were asked for proof of permission to film indicated how closely the public is watched.
Without the required permission from the Ministry of Culture we would have been arrested.
On one occasion, unpleasant plain-clothes officers detained us at major shopping district.
The "main man", probably from the Intelligence Division, seemed to take great pleasure in telling us he had the power to arrest us - even if we had filming permissions and press cards.
Yet, what is irrefutable is this: the ability of the Iranian government to both control and influence people has been weakened by the internet.
How the Iranian clerical and political establishment choose to respond to that formidable and growing challenge will be fascinating to watch.