Ethics is two things. First, ethics refers to well-founded standards of right and wrong that prescribe what humans ought to do, usually in terms of rights, obligations, benefits to society, fairness, or specific virtues.
If you mean the average speed limit, it's probably 65 MPH. In 1995 Congress repealed the national speed limit of 55 and it is now up to states again to determine the limits. About 30 states have limits of 70 MPH or higher. A few Western states have no speed limits on certain stretches of highway.
UK speed limits are shown in mph. With a few exceptions, they are in multiples of 10, ranging from 20 miles per hour (32 km/h) to 70 miles per hour (113 km/h). Unless a lower speed limit is posted on a road, the national speed limit applies, which varies between class of vehicles and the type of road. In a built-up area (usually indicated by street lights), unless signs indicate otherwise, a limit of 30 miles per hour (48 km/h) applies. Other limits are shown in the table.