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 In 1995 Congress repealed the national speed limit of 55 and it is now up to states again to determine the limits.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.
The first maximum speed limit of 10 miles per hour, (16km/h), was introduced in the United Kingdom in 1861. In 1901 the State of Connecticut introduced the first United States state law regulating motor vehicles. The maximum speed limit in the cities was set at 12 mph and 15 mph outside the cities.