As a Pennsylvania driver, no one need tell you about the frustrations of sharing our mountainous roads and highways with 18-wheelers, especially when you get stuck behind one on an uphill grade and another one blocks your passing lane. Your natural tendency likely is to get around both of them at your very first opportunity and leave them receding in your rearview mirrors.
Before passing any semi, let alone two of them, on a downhill grade, however, you should know that the possibility of a jackknife increases dramatically under the following three conditions:
- Steep downhill grade
- Curve or turn
- Icy, snowy or wet road
If more than one of these conditions exists at the same time, the possibility of your becoming a jackknife accident victim increases exponentially.
Mechanics of a jackknife
A tractor-trailer jackknifes when its trailer wheels lose traction with the road and keep going straight ahead regardless of the direction of its cab. The trailer starts to fold in on the cab in much the same way as your pocket knife closes. The angle between them becomes ever more acute. But whereas your pocket knife handle has a slot into which the blade goes, the truck’s trailer has nowhere to go other than crashing into the cab. The resulting injured truck and its debris can easily reach across two lanes of traffic, causing a more or less immediate pileup.
A jackknife is a completely out-of-control phenomenon. No one, not even the truck’s driver, can anticipate exactly what a jackknifing truck will do or where it will do it. This makes a jackknifing accident one of the most potentially deadly motor vehicle accidents since no one has much of a chance to prevent or avert it. Given that the tractor-trailer weighs about four times as much as your passenger vehicle, this puts you and your passengers at exceedingly high risk for catastrophic life-threatening injuries.
Consequently, your best strategy when coming up on an 18-wheeler is to control your frustration and never pass it on a curve, when it is attempting to turn or when the road is particularly wet or slippery. Even on a straightaway in the best of weather, give trucks the widest berth possible when passing them.