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 In 1995 Congress repealed the national speed limit of 55 and it is now up to states again to determine the limits.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.
All of the roads in the US have a speed limit, the average being around 75 mph, with some areas in Texas and Utah reaching 80 mph. Road speed limits are used in most countries -- and are endorsed by the World Health Organization -- as a way to reduce road casualties. The highest speed limit ever introduced was in Abu Dhabi between 2005 and 2010 where the limit was set at 99 mph. The speed limit was reduced in 2011 to 87 mph. In Germany, some autobahns have no speed limit, but an advisory limit of 130 km/h (80 mph) was established in 2008.