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 In 1995 Congress repealed the national speed limit of 55 and it is now up to states again to determine the limits.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.
Most speed limits are set by state or local statute, although each state allows various subdivisions (counties and municipalities) to set a different, generally lower, limit. The highest speed limits are generally 70 mph (113 km/h) on the West Coast and the inland eastern states, 75â80 mph (121â129 km/h) in inland western states, along with Arkansas and Louisiana, and 65â75 mph (105â121 km/h) on the Eastern Seaboard.