OSLO (Reuters) - Norway’s high school graduates should refrain from running naked across bridges and having sex on roundabouts lest they give drivers “too much of a surprise”, the national transport regulator said on Wednesday.

Norway’s annual post-graduation period called “Russ” lasts weeks, involves partying and drinking heavily - and tends to challenge public morals every spring.

Dozens of accidents involving students’ red- or blue-painted vans and buses are reported every year, and sometimes the celebrations lead to crashes killing those aged just 18 or 19.

While the list of rituals involved in the Russ celebrations vary from one school to the next, they almost invariably involve alcohol, nudity and sex.

In a statement titled “No to sex on roundabouts”, Terje Moe Gustavsen, a former minister of transport who now runs the Public Roads Administration, said: “Everyone understands that being in and around roundabouts is a traffic hazard,” .

“It may not be so dangerous for someone to be without clothes on the bridge, but drivers can get too much of a surprise and completely forget that they are driving,” he added.