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 In 1995 Congress repealed the national speed limit of 55 and it is now up to states again to determine the limits.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.
Section 3: Safe Driving Speed Limits A speed limit is the maximum legal speed you can travel on a road under ideal conditions. You may drive slower than the posted speed, but it is illegal to drive any faster. By law you must drive slower where signs indicate a school zone speed limit or work zone speed limit is in effect, and/or if conditions