Utah is already at the high end of the spectrum in speed limits. Only Texas has an 80 mph limit, and only for cars during daylight hours. Other Western states' rural interstate speed limits are uniformly set at 75 mph, the same as Utah's.
It seems logical to assume higher speed limits would boost accident rates, but, surprisingly, studies show that raising or lowering speed limits by 5 or 10 mph on interstates has little effect on most motorists' driving habits or on accident rates.
One Utah legislator, Rep. Ron Bigelow, R-West Valley City, said he has observed that Utah drivers tend to drive 5 to 10 mph over the speed limit. If that is, indeed, true in Utah, then drivers in this state are different from drivers elsewhere.
Studies show if speed limits reflect the optimum speed for safety on a given stretch of road, then most motorists drive reasonably close to the posted limit.
It does not work to try to reduce driving speeds by lowering speed limits. By the same token, raising the speed limit by 5 mph would not change the speed that most drivers drive. But it could appear to entitle irresponsible drivers to exceed the speed limit by even more than 5 mph.
One good reason not to encourage even a few drivers to go faster is the air pollution caused by higher speeds. Increasing speed by 5 mph cuts fuel economy by about 6 percent. Using more fuel puts more emissions into the air.
That may not seem to matter much on the stretch of I-15 that HB 406 targets - areas between Nephi and Cedar City. There are no big population centers there resembling pollution-clogged Salt Lake Valley, to be sure.
But carbon emissions are increasing worldwide, causing global warming with its weather changes, drought and water shortages. If most motorists drove more slowly, closer to the optimum speed for the best mileage, around 55 to 60 mph, there would be a significant reduction in carbon emissions.
That kind of change would be difficult to enforce in rural Utah, and nobody is proposing it.
But Utah's current 75 mph speed limit on the rural Interstate allows people to travel north and south through the state at a speed that seems reasonable.
Why change it?
