Swiss authorities are basking in the afterglow of their decision last year to create a sex drive-in in Zürich, with social services hailing it a success on its first anniversary on Tuesday .

Zürich's experiment began last August when the authorities opened Europe's first municipal drive-in brothel in an old industrial area to the west of Switzerland's largest city, complete with helpful signposts and understated wooden drive-in "sex boxes".

Sex workers who agreed to relocate from their traditional city-centre haunts were allowed to ply their trade at the brothel safely and with a minimum of fuss.

First, however, to avail themselves of the drive-in's creature comforts – which include a laundry, shower facilities and cafe – they had to obtain permits and pay tax.

"The new regulation of street prostitution has attained its objectives of protecting the population and the sex workers," the city said in a statement.

Social services said that, as well as protecting sex workers, few neighbours were bothered by the comings and goings at the drive-in, in the Altstetten district.

No increase in street walkers had been noticed in the two other districts of the city where prostitution was tolerated, they said.

"The first year of the service has been positive," Zurich social services said.

The number of sex workers working at the drive-in averaged 15 a night, half the number who worked the old red-light area before the city stepped in to regulate the business.

However, the authorities admit that not everyone is happy. Some sex workers complain that their earnings have fallen and that they are too far from city-centre bars and nightclubs.

And running the drive-in – which has cost around €2m (£1.59m) to set up – has proved more expensive than originally thought.