Since the beginning of June, Germany has sold a monthly ticket for nine euros ($9.21) that is valid for unlimited trips on a vast swathe of its public transport network. The offer, which continues through August, was designed to take the sting out of soaring inflation and cut vehicle emissions.

It was a bold move for the home of automakers BMW, Mercedes and Volkswagen, where drivers famously have no speed restrictions on stretches of motorway.

Mohawk-wearing punks from around Germany took advantage of the cheap tickets to flock to the upmarket resort island of Sylt last month. But it was unclear whether most travellers would park their beloved cars and board buses, trams and trains.

While it is still early to draw conclusions, data compiled by the navigation company TomTom for Reuters suggest the policy may be having an effect.

During the week of June 20, rush-hour traffic congestion was down in 23 of 26 cities compared with the week of May 16, before the new ticket was introduced, the data show. TomTom chose the two weeks because they were both free of holidays.

"This decline is related to the introduction of the nine-euro ticket," said TomTom traffic specialist Ralf-Peter Schaefer.

Other factors may also play a role in the reduction, such as high fuel prices and pandemic-related work from home trends.

But TomTom data for the full month of June also show lower congestion compared with both May this year and June 2019, before the pandemic: congestion was down in 24 of 26 cities in June from May, and in 21 of 26 cities versus June 2019.

The findings could interest policymakers weighing possible future measures for low-cost public transport beyond August.

"If I were the government, I would really think hard now," said Schaefer.

The cheap ticket has also spurred train usage, which was up 42% in June from the same month in 2019, according to Germany's statistics office.

The rise has been most marked at weekends, leading to complaints from some passengers about overcrowding.

In 2020, Luxembourg became the first country to make public transport free. Officials there have reported increased tram usage, and TomTom data show congestion down in recent months from pre-pandemic levels.

But it may be an uphill battle to wean some Germans off their cars. TomTom's Schaefer said he still preferred to drive to his Berlin office to save time on his daily commute.

($1 = 0.9770 euros)