The German autobahns are famous for being some of the only public roads in the world without blanket speed limits for cars and motorcycles, though traffic on them is usually heavy enough to restrict speeds to little above the typical motorway speeds found elsewhere. However, speed limits do apply at junctions and other danger points, like sections under construction or in need of repair. (Speed limits at non-construction sites are generally 100 km/h or 120 km/h; construction sites have an usual speed limit of 80 km/h but may be as low as 60 km/h or even 40 km/h. Certain stretches have separate, and lower, speed limits used in cases of wet lanes.) Some limits were imposed to reduce pollution and noise. Limits can also be put into place temporarily through dynamic traffic guidance systems that display the according traffic signs.
It is important to remember that in places without a general limit, the overtaking is not limited either. So everyone who is speeding at will has to beware of trucks running side by side at roughly 80 km/h (50 mph). In theory, trucks are not allowed to overtake others if they don't drive 20 km/h (12 mph) faster than the truck on the right lane, but truck drivers are under pressure to arrive in time. Police don't enforce this for economic and political reasons, as many trucks are from foreign countries. Basically, apart from on Sundays, the right lane of German Autobahn are crowded with trucks, and too often, they pull out to overtake.
Modern cars easily reach well over 200 km/h (125mph), and most large car manufacturers follow a gentlemen's agreement by artificially limiting the top speed of their cars to 250 km/h (155mph) for safety reasons (inexperienced drivers and risk of tire failure especially when underinflated). Yet, these limiters can easily be removed, so speeds over 300 km/h (185mph) are not uncommon nowadays. But due to common speed-limits and other traffic no one should expect to be able to drive such speeds.