The section of the Autobahn has an 80km/h speed limit
A skateboarder who was filmed riding on a German motorway at 100km/h (62mph) is being sought by police.
A video showing the helmeted man hurtling along the Ulm-Stuttgart motorway in the south of the country has been broadcast on German TV.
The man, who held on to a motorbike to build up speed, could face a hefty fine for speeding and endangering other motorists.
Police believe he may be a professional stuntman.
"We put out an all-points bulletin and have received information that gives us useful clues to who the man may be," police spokesman Uli Stoeckle told Reuters.
"We are particularly concerned about copycats who may imitate the stunt, putting their lives at risk."
The skateboarder raced down the road, in Goeppingen near Stuttgart, for about 3km (two miles) before pulling up.
A video of the stunt has surfaced on the video-sharing website YouTube.
The video carries a warning saying: "Dangerfreaks is performed by professional stuntmen, so it is not recommended to try this at home".
Although most German motorways have no speed restrictions, the stretch the skateboarder was on has a limit of 80km/h.