The German Autobahn is the equivalent of the Dwight D. Eisenhower National System of Interstate and Defense Highways, which is the official name of our Interstate highway system. The official name of the Autobahn is Bundesautobahn, which translates to "federal auto track" or "federal roadway." The Autobahn is about 8,000 miles of federal highways. While there are no blanket speeds on the autobahns, only about 55% of the autobahn has literally no speed limit (for cars). In urban and congested areas there are posted speed limits. And on the autobahn and other roads in Germany where there is a posted speed limit, it is rather strictly enforced, where as little as 2 MPH (3 km/h) over the limit will get you a pricey ticket. Where the autobahns have speed limits, they are 50 km/h (31 mph) inside city and urban areas, 100 km/h (62 mph) outside built-up areas, and 130 km/h (81 mph) in rural areas.
The German Highway Code begins with "Any person driving a vehicle may only drive so fast that the car is under control. Speeds must be adapted to the road, traffic, visibility and weather conditions as well as the personal skills and characteristics of the vehicle and load." If you fail to adhere to this and get into a speed-related accident, it's pricey, and you are likely to lose you license.
For trucks on the autobahns, even in places where there are no speed limits, the speed limit is 80 km/h (50 mph). Trucks over 3,500 kg (7,716 lbs) are required to have a built-in speed limiter for a maximum speed of 90 km/h (56 mph). On non-autobahn roads, trucks with a GVRW of 7,500 kg (16,534 lbs) the limit is set to 60 km/h (37 mph). So when people complain about split speeds here, it's nothing compared to the split speeds of Germany.
They key to Germany's low accident and fatality rate is what they call the Four Es - Enforcement, Education, Engineering, and Emergency response. Here in the US we just have the Two Es - Enforcement and Emergency Response. <snort>