The lonely stretches of I-15 in central and southern Utah had their own, unofficial speed limit all along. It just took awhile for state government to find it.

Last year, the state Legislature agreed to allow an 80 mph posted limit on two stretches — one around Scipio and the other near Fillmore. These were experiments, and the Utah Department of Transportation was supposed to report back on results. That report took place this week.

Turns out 80 mph is just about the natural limit on those stretches, where twists and turns are sparse as trees. UDOT said the average speed there was about 81 to 85 mph back when the speed limit was 75. Once it bumped up to 80, the average over time came in at 83 to 85 mph — no change. It's not surprising, then, that the higher speed limit didn't lead to a higher rate of accidents, either.

On average, people apparently aren't interested in going much faster through those areas, no matter what the posted limit. Motorists will, of course, chime in with anecdotes of nearly being mowed down by speeders even in the 80 mph zones, but reckless drivers would behave like that no matter the official limit.

Speed limits can be elusive targets. Regardless of the law, people tend to move along at a rate they feel is safe and in keeping with surrounding traffic, with one eye out for police cruisers, of course.

Now that some data are in, it seems clear that well-constructed interstates, such as I-15, should be given higher posted limits on stretches where those speeds can be negotiated safely. Elsewhere, they ought to remain lower.

Uninformed voices will cry, "Speed kills." In truth, there is no evidence this is true. The latest report from the National Highway Traffic Safety Administration shows highway deaths on a steady decline. In the first half of 2009, 16,626 people died on the highways. That's a 7 percent decline over the previous year. The second quarter of the year marked the 13th straight quarter of declines when compared with the same quarter during the previous year. The nation is on track for about 33,000 deaths this year, compared to 51,093 in 1979, when speed limits were 55 mph and fewer people were on the roads. "Speed kills" is simplistic and wrong.

The only concern created by higher limits, UDOT said, is that it increases the differences between fast- and slow-moving vehicles. A car zipping along at 80 mph can come upon the rear end of a lumbering truck quickly. But then, those differences already exist, because drivers apparently are going to travel I-15 at the same speed, regardless of what is posted.