An initial 60m (197ft) stretch of the “green rails” has already opened in Sofia’s Ruski Pametnik Square. Architects hope the new turf will muffle traffic noise, improve air quality and cool the often torrid Sofia summer heat, Nova TV reports. A drainage system has been installed to divert rain water off the rails into the soil beneath the grass.

Although other vehicles will use the square for the time being, the authorities want to include it in a car-free zone which will cover three blocks in the city centre by 2020. Other tramways elsewhere in the zone will be grassed over too, according to the plan.

Many social media users like the idea, thinking it will give Sofia a “more European” eco-friendly feel, although some see it as no more than an election stunt by the city’s governing Gerb party.

“The rails will stay green only until after the election,” says one person on the Dnevnik newspaper website.

Plenty of others worry that the grass will be left to dry out and turn yellow, with one reader on the Vesti website warning: “Nice dry grass needs only one cigarette butt, then we’ll see the spectacle of trams passing through flames.”