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 In 1995 Congress repealed the national speed limit of 55 and it is now up to states again to determine the limits.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.
Congress repealed the National Maximum Speed Limit in 1995. Since then, 34 states have raised speed limits to 70 mph or higher on some portion of their roadway systems. Several states have set different speed limits for cars and trucks. Speed limits may vary depending on whether the roadway is urban or rural.