Along Montana state highway 59 between Jordan and Miles City - an 86-mile stretch of two-lane blacktop running arrow-straight from horizon to horizon - it's possible to test the aerodynamic limits of one's automobile.
It's possible, I can write with some authority, but it would be wrong to do so. For no matter what you may have heard or read, Montana does, in fact, have a speed limit.
When Congress and President Clinton last year lifted the federal limit on highway speed imposed during the oil embargo of the 1970s, many Westerners rejoiced. At least a dozen states raised limits to 65, 70, and even 75 miles per hour.
But Montana went further: It reverted to its old law mandating only that the speed of cars and light trucks be held to a velocity that is "reasonable and prudent."
And just how is this non-numerical speed limit defined? It includes weather, road, traffic, and vehicle conditions, but it's really a judgment call by Montana Highway Patrol officers.
Since there are just 212 uniformed highway patrol officers ("Including me," says Col. Craig Reap, chief patrolman), and since there are more than 50,000 miles of primary roads and interstate highways, there's plenty of wide open space between possible speed traps.
For the first five months under the new law, there didn't seem to be much change in driving habits here.
According to state highway department surveys, the average auto speed only crept up from 72 miles per hour to 74 - which can seem fairly poky in parts of "Big Sky Country." Highway fatalities actually remained lower than during the same five-month period in 1995. It seemed that all those Jay Leno jokes about the "Montanabahn" had been proved wrong.
But then vacation season hit, and Montana began getting its annual influx of several million visitors headed - quickly - to national parks and other recreation sites.
At the same time, a difference of opinion developed between state agencies about exactly how fast even Montanans had been traveling under the new law.
"Speeds are up a lot more than what is indicated by these very, very limited surveys that the department of transportation does," says Colonel Reap, who just finished a tour of the state. "We estimate that speeds are up in the high 70s to low 80s with some very, very excessive speeds showing up a lot more often than they ever had before - speeds in excess of 100 miles per hour."
Part of the problem is that many of those speed-reading devices embedded in the highway max out at 85 miles per hour. In other words, Reap says, "They don't differentiate whether it's 86 or 105."
In addition, highway fatalities here have crept back up above last year's level: 88 as of the morning of July 8, compared with 85 during the same period in 1995.
This concern has prompted a Montana public-information blitz launched last week to let all drivers here know that there is a speed limit and that breaking it can cost up to $500 plus a black mark on your driving record. The campaign includes billboards, fliers handed out at visitors' centers, bumper stickers, public-service announcements, and T-shirts.
The tone and approach thus far is friendly. "We're just trying to raise the level of awareness so that all of our good friends and neighbors from outside the state of Montana will have the same information and the same expectations that those of us here do," says Gov. Marc Racicot (R).
But the word is out that if you're not "reasonable and prudent" on Montana highways, you could be in for an expensive lesson. Warns Andrew Warner on the Montana section of the "Speedtrap Registry" he set up on the worldwide web (http://www.speedtrap.com/speedtrap/): "If you get pulled over, you will get a ticket, and it will be costly."