Being designed for speed and driving at that speed are 2 different things. If the police needs to get to a dangerous situation or ambulances need to drive at high speeds than it would be a real disaster if the road would make this impossible, but police officers and ambulance drivers are trained to drive at such high speeds and have light and sound warning systems to warn other that they are coming at high speeds. It might be able to drive faster and even drive faster than 100mph but it does not mean that normal drivers should drive at speeds that high. It would be a different thing if there were 3 or 4 lanes in which cars would only be allowed to drive on those lanes if they were driving 90 miles or more. It should also be illegal to drive on that lane at speeds under 90.