Average interstate speed is between 65 and 70, and that's what auto manufacturers design for

Many urban Americans' primary contact with rural America is on the Interstate highways strung between metropolitan areas. For rural Americans, the roads are increasingly routes to work, health care, culture, recreation and relatives. We rarely meet on the road, but we share its rules, and even help change them. We have effectively increased speed limits. Anyone who drives these roads much knows that; now we have data to suggest a consensus limit: 70 miles per hour.

TomTom Inc., which makes devices using the Global Positioning System, has analyzed data from customers in 45 states who agreed to have their driving anyonmously monitored to help the company steer customers away from routes that become congested at certain times. "The TomTom data suggest that most drivers tend to stay within a few miles per hour of the speed limit on major roads. In 31 out of the 46 jurisdictions, average freeway speeds ranged between 65 and 70.1 mph," with the highest speed in Mississippi, Joseph B. White reports for The Wall Street Journal in his Eyes on the Road column. (WSJ map; speed limits vary)

"This helps to explain why safety advocates and conservationists are losing the long-running debate over ... freeway speed limits," White writes, noting that Virginia last week raised the speed limit on rural interstates to 70 from 65 mph. "Virginia will become the 34th state to boost interstate speed limits to 70 mph or higher. In big, empty states such as New Mexico, Idaho and Nevada, posted limits on rural interstates can be as high as 75 mph." White notes that most cars and light trucks "are designed to cruise comfortably, safely and efficiently at between 65 and 70 mph." (Read more)