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 In 1995 Congress repealed the national speed limit of 55 and it is now up to states again to determine the limits.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 speed limit for most business and residential areas is 25 mph. On secondary roads (those routes numbered 600 and above, with one exception), the limits are 45 mph for trucks and 55 mph for other vehicles. Effective July 1, 2014, a maximum speed limit of 35 mph applies to all unpaved roads statewide.The road does not have to be posted.