How fast is fast enough? It’s a legitimate question being pondered and voted on by Idaho lawmakers. Senate Bill 1284, sponsored by Senate Majority Leader Bart Davis, (R)-Idaho Falls, is on a fast track, owing to no particular study or interest group, save perhaps the need to stay abreast with Utah.

There, the magic number—for the moment, at least—is 80 mph on selected roads. The only other state in that rarified air is Texas, where some roads are open to 85 mph cars. Other states may be contemplating the move, but for now Idaho is on the short list to make it happen.

Why the rush? That’s another legitimate question AAA asked the sponsor. Raising speed limits isn’t on the radar for 120,000 AAA members. We didn’t ask for it. We weren’t consulted. Some may secretly hope the bill passes, but it’s not our priority.

And the last time the state was considering higher speed limits for trucks on the interstates, our conversations with the long-haul shippers indicated they weren’t interested in going faster either. In fact, the industry’s widespread use of speed limiters means these trucks are operating between 62-64 mph. They’re maximizing efficiency, holding fuel costs down. That makes sense.

That’s not to say that all trucks drive at the posted limits—or cars for that matter—but consider the 2012 findings of a stakeholder group convened by former Sen. Jim Hammond on the topic of higher limits for trucks. Both AAA and the major Idaho based trucking company represented expressed concerns that widening the gap between the slowest and fastest vehicles on the interstate could result in more potentially dangerous interactions, not fewer. That concern is valid with SB1284.

This bill defers all final decisions about which roads may qualify for higher limits to the Idaho Transportation Department, ostensibly to limit potential political conflicts. That sounds reasonable, yet even the experts disagree on the potential impacts of higher limits. The U.S. DOT says speed limit studies study contain major contrary conclusions that are not supported by empirical, verifiable, and scientifically valid data!

There’s a notion everyone drives 80 mph already, but a 2012 speed limit study prepared by the University of Idaho for ITD shows otherwise. Idaho raised its maximum limits to 75 in 1996. Between 1997 and 2011, Idaho’s mean speed for cars on selected segments of the interstate has stayed relatively flat, not bouncing much above 75 mph. The same is true for trucks, where the mean speed on selected routes in 2011 was at 65.5 mph.

So why is Idaho in such a hurry to consider higher speed limits? Are we unsafe now? Will we be safer when we can legally go faster? Is it an issue of convenience? Do we need to get farm products to market quicker? Give us some confidence that this idea makes sense.

And since it’s not just about the interstates, are we ready to make 70 mph the posted, legal speed for cars and trucks on State Highways 20, 21, 75 and others?

As AAA also said in testimony to the Senate Transportation Committee, factors like current enforcement, night driving, weather and terrain all may affect safety, but are not specifically spelled out in the bill. Consider that at 80 mph, vehicles may overrun their headlights at night.

When it comes to opening the door to new higher limits, legislators would be wise to proceed with caution.

Dave Carlson is director of public and government affairs for AAA Idaho.