Last week, the Illinois Senate opened discussion that could lead to the state increasing the speed limit on some stretches of highway to 70 mph.

Before this debate heats up — and we’re confident it will — we’d like to establish two points.

No. 1: There are many valid arguments in favor of raising the speed limit on non-urban highways from 65 to 70 mph. We’ll get to those momentarily.

No. 2: Increasing highway safety is not among the arguments in No. 1.

In his testimony last week before the Senate Executive Committee, the speed limit bill’s sponsor disputed the notion that raising the speed limits equates to more traffic accidents.

“A lot of times, individuals will be speeding when the accident took place, but it was not the cause of the accident itself,” said Sen. Dale Risinger, R-Peoria.

Well, that’s one way to look at it. The Center for Transportation Research and Education at Iowa State University released a study in 2009 that offers another view. The center studied traffic accidents on rural Iowa highways where the speed limit had been raised from 65 mph to 70. It used data for 2 1/2 years before and after the new limit went into effect on July 1, 2005.

“Fatal crashes increased on average from 19.2 to 25.2 (an increase of 6.0) per year resulting in a 31.3 percent increase when compared to the 2½ year before period,” the study says. It also examined data that included all serious crashes: “Serious (fatal and major injury) crashes increased on average from 78.8 to 90.8 per year (an increase of 12.0), resulting in a 15.2 percent increase when compared to the 2½ year before period.”

The problem with the Iowa study — and many statistical breakdowns of traffic accidents — is that it deals strictly with numbers. Though the numbers would seem to indicate that the new speed limit led to more accidents, we don’t know what other factors were involved. How many of the injured or killed were wearing seat belts? Were they driving above even the posted speed limit? Was alcohol a factor? In exactly how many of these accidents was traveling at 70 mph versus traveling at 65 mph a contributing factor?

So Risinger has a point in saying that “a lot of times” speed alone doesn’t cause the accident.

Of course, anyone who has driven a motor vehicle knows that it is not easier or safer to avoid a deer in the roadway at 70 mph than at 65 or slower. But, statistically speaking, do such factors outweigh the benefits of driving faster on long, straight, boring stretches of rural interstate? We haven’t found that study yet.

The Illinois Department of Transportation and Illinois State Police believe the risks are greater than any perceived benefit, and are opposed to raising the limit.

But we also know this: Except for Wisconsin, all our neighboring states have set 70 mph as the speed limit on rural interstates. It’s an annoyance to drivers crossing into Illinois on, say, I-55 from Missouri or I-64 from Indiana, to have to slow from 70 to 65 for the long, flat trip through Illinois. Illinois drivers also may wonder why they could drive 70 mph in hilly West Virginia yet they can go only 65 on the tedious stretch of I-39 between Bloomington and Rockford. And when drivers find speed laws annoying and/or illogical, they tend to disregard them.

The last time this debate raged in Illinois was in 1987, when the state raised the speed limit to 65 mph. By 1990, there were fewer traffic fatalities in Illinois (1,589) than there had been in 1986 (1,617) under the 55-mph limit. By 2009, the traffic death toll on Illinois roads was the lowest in 88 years.

What happened? We started wearing seat belts. Seat belt use in Illinois last year was 91 percent, according to IDOT. In 1987, it was 36.2 percent. We’re also driving safer cars equipped with airbags. Anti-DUI efforts are much stronger now.

This new attention to safety should factor into discussion of statistics as the debate over a new speed limit gets under way.

Our observations suggest drivers already are voting with their accelerators on Illinois highways, which to us is an indication that the official move to 70 mph eventually will happen. We hope Risinger’s bill gets a vote this session, but supporters should not soft-pedal the fact that with more speed will come more risk.

State Journal-Register