There has been some interest as to the particulars of the abbreivated off-ramp negotiation mentioned. I apologize for not embellishing profusely on the subject, but I was just on LJ to get a quick fix. To tpbrcombo and spleazeball, just remember, you asked for this.
When Bob and I left Indianapolis yesterday morning we drove for about 45 minutes then stopped in Seymour for fuel. This was to be Bob's first time driving since getting out of trucking school last week, not to mention, in a totally different truck and transmission from the one he learned on. The off-ramp at the Seymour exit is a standard cloverleaf exit with a gradual arc for the exit on one side of the overpass and a sharp, banked ramp on the other. The on ramps are mirror compliments with the "leaves" situated inside the arcs, giving it that comforting symmetry from the air.
Here's an aerial photo of the I-494/I-35W interchange in Bloomington, MN outside Minneapolis near the Mall of America for reference, in case you can't picture what I mean.
It was an off-ramp "leaf" we needed to use to get to the truckstop. Bob had learned to drive in a Volvo, which has a service brake similar to the brake pedal in a car; it rests on an arm with a small footpad attached to it. In a Peterbilt, however, the break pedal is identical to the fuel pedal in size, shape and mechanics; it sits on a hinge which is attached to the bottom of it on the floor and is very long and wide. This type of pedal is also referred to as a treadle valve. Any of you who are guitarists or sewing enthusiasts should know what a treadle pedal is like. This is exactly the way a Peterbilt's brake pedal is, only bigger.
Obviously, Bob had used the brake already when leaving the previous truckstop, but it was pretty much at idle speeds: exiting the parking lot, slowing for the turn onto the freeway ramp. This was the first time he would take the truck down from 65mph to the suggested 25mph for the off-ramp in Seymour. This is the first part of the problem, not being familiar with the equipment.
The second part of the problem is that, with new drivers, one of the hardest things to learn is how to downshift. A commerical road tractor doesn't just have a really big passenger vehicle's transmission with more gears. It is synchronized. In a manual transmission car, you can pretty much put it in any gear, any time, at any speed as long as you press the clutch and put it there. You can be going 70 mph, put it in first gear and pop the clutch if you wanted to. Your engine would blow itself out the tailpipe, but you could do it if you so desired. In a truck you can't do that. The rate of revolutions of the drive axle (your road speed) has to be synchronized with the rate of revolution of the engine (RPM's) for the gear. It is impossible to achieve enough RPM's to put a truck in second gear when you're moving 55mph. Similarily, you cannot slow the RPM's down enough at 10 mph to throw it in ninth gear.
If you are already in gear, it winds out at the high end of the gear and begins to lug at the low end. At the low end, a truck can even pop out of gear if your speed drops too low for that gear. When you are not in gear (like when you are switching gears) you have to make the RPM's match your current road speed by revving the engine with the fuel pedal or letting them "fall" by waiting a few seconds between gear shifts. To put it in the simplest terms I can: when you are upshifting, the RPM's have to go "down" and when you downshift, the RPM's have to go "up". Up/down, down/up. A truck clutch also has three different positions over the course of their range of motion. In order they are the "play" (dead space at the top), the "engage" area in the middle (for shifting gears), and the clutch brake all the way at the bottom (for stopping transmission gears when idling). This can be particularly frustrating and the source of lots of burned-up clutch brakes; people who have driven manual transmission cars prior to their career as a truck driver. Also... the shifting pattern for a "straight" truck transmission (as opposed to a "super" pattern), while essentially is like a passenger vehicle, has a high and low range. The positions are stacked on top of each other and you use a "splitter" on the stick-shift to differentiate between the two ranges. The positions for gear 1 is the same for gear 5. Also, 2 and 6, 3 and 7, 4 and 8. Depending on whether your "splitter" is up (high) or down (low) will determine what gear the transmission will try to go in at each position. Really, the only time you have to use the splitter is when moving between gears four and five, but when in the heat of downshifting with all these different things to remember and perform simultaneously, it's easy to forget in what gear you actually are. So the splitter often gets switched when it's not supposed to. My transmission is also a "top 2 automatic". Eighth gear is also ninth gear, it switches back and forth automagically. Confused yet?
On top of all of this, if you are driving in "textbook" fashion and not floating the gears (a whole other topic that doesn't really relate to this story), you have to double-clutch: once when you leave the gear, then achieve the required RPM's, then clutch again and put it in your new gear. When climbing through gears, letting RPM's "fall" is a very natural thing to do, so most new drivers don't have much problem with upshifting. You let the motor wind-up, clutch the transmission and let the RPM's "fall" somewhere between 300-500 RPM's of the current RPM's, then clutch again and shift into the next gear.
When downshifting though, not only do you double-clutch, but your right foot becomes involved because you have to GIVE the engine 300-500 RPM's. And since you downshift when you are decelerating, usually you are also co-ordinating your right foot between the two treadles. The basic process works like this: brake, clutch, shift, fuel, clutch, shift and then repeated for as many gear shifts are required. Feel free to refer back to this process in a moment.
It is not uncommon for new drivers to "lose their gear". In truck driving school they even teach you "gear recovery" techniques. When a truck is not in gear, you are considered to not be in control of your vehicle. Being out of gear for more than one tractor-trailer length of movement is typically an automatic failure on a DOT road test. At high speeds, this is a matter of seconds. I've found that most new drivers lose their gear because they don't perform the proper process. Their process usually looks something like this: clutch, shift, fuel, clutch, shift, grind gear, more fuel, clutch, shift, grind gear, look at me like the truck doesn't work the way it's supposed to while still rolling at the current rate of speed and closing the gap between us and whatever we're slowing down for. Again, at high speeds, this is a matter of seconds. They always forget the brake.
Let's put it this way. It takes the length of a football field for a fully loaded tractor-trailer to safely brake to a complete stop when travelling at 60mph. It takes even longer with an empty trailer. It takes even longer than that when bobtail (sans trailer). You know the "two second" following rule they teach you in Driver's Ed? It's eight seconds in a tractor-trailer travelling at 60 mph. Think about that the next time you cut-off one of them big boys on the freeway then hit your brakes.
So, the first time a new driver is making his first big deceleration and downshift, I remind them of this process way ahead of time. We talk about it and then I also talk them through it as they are performing it. As you may recall, the fuel pedal and service brake are both treadles of equal size and shape in a Peterbilt and are only about a half-inch from each other on the floor. You can see where this is going now, can't you?
As Bob approached our cloverleaf I began to talk him through the process. This will always be "our cloverleaf". There was a bobtail in front of us, also exiting on our cloverleaf. I don't think he took the term "now" with the gravity I intended to convey when I told him to begin braking-down so he could get his next gear. His mind was focused on the complicated process of downshifting and he made that rookie mistake of removing his gear before lowering his road speed. They always forget the brake. He's rolling toward the off-ramp, out of gear and grinding it like he was making sausage. In a situation like this, it does no good for me to become excited or animated... that will only exacerbate the problem, so I avoid it when possible. Now white-knuckling the door handle, I remark that he needs to get his speed down, now. Actually, it just came out as "Brake!".
Having been snapped out of his lost gear confusion, he attempted to apply the service brake. He hit the fuel treadle, since that was where his foot was trying to give the truck RPM's for the downshift. When that didn't work, he stomped the fuel treadle, assuming that he wasn't giving it enough application. If there was ever a time when I was glad that my student had lost his gear, it was now. By this point we are in the merge area of the overpass where the two cloverleaves meet on the highway and entering the 25mph curve at 60mph, closing in on another vehicle. Realizing his footwork error and with the prospect of simultaneously proving Newton's First Law AND Pauli's exclusion principle, he stomped the brake. And I mean stomped. I heard myself calmly saying "Don't lock it up" while checking the trailer in the mirror. I expected to see the side of it moving toward me, but thankfully this wasn't the case. He somehow managed to get control of the speed enough so that we coasted through the rest of the ramp until he was able to recover his gear.
I thought for sure we were going to leave the road. Call it luck or divine intervention because, by all estimations, we probably should have.