Archive for April, 2009|Monthly archive page
I’ve *finally* gotten around to adding an index page. If you were looking for a specific post, you had to wade through the lot to find it. To use it, just click on the index tab above.
a story at:
tells of four states that are going to spend $5 million to study adding truck-only lanes to I-70.
Nice, but there are much worse things that really need attention. What would be much more useful is a truck express route through Chicago. Run it from I-65 in Indiana, to I-94 in Wisconsin. Have another leg go out to I-80 west of Chicago. Run a third to I-90 also west of Chicago. Building truck express lanes in those corridors would save thousands of truck hours every day. Oh, but wait a second — that would be intelligent, logical, and efficient. Since those three things seem to be in rather short supply when it comes to transportation planning, I guess it probably won’t happen.
Of course, wherever it’s decided to put truck express lanes, they will almost certainly be funded by tolls — and probably fairly expensive ones. That’s ok — I’ll just pass along those exorbitant tolls to you — in the form of higher freight rates, increasing the cost of everything that moves through any toll corridor.
Comments and questions welcome.
Here’s a story about a truck wreck in La Canada, California.
The usual response from the public would be a bunch of whining, and maybe the restriction of the route to truck traffic. Instead, 16 year old Girl Scout Malia Mailes created an excellent presentation about the problem, along with some constructive solutions. You can see her presentation here:
There are a couple of things in her presentation that are inaccurate and need explanation.
Slide 9 of Malia’s presentation shows the route in question in yellow, with a red “38” below. This denotes that trucks using the route must be “California Legal” with a 38 foot KPRA. This does NOT mean a truck 38 feet long.
This shows that “California Legal” means a truck with a maximum 65 foot length, and a KPRA of up to 40 feet. So, what’s KPRA? KPRA is the distance from the KingPin to Rear Axle. This distance is relevant, because it determines how much a trailer will off-track in turns. On a highway with tight curves, a trailer with a long KPRA can off-track into the oncoming lane, or off the road on the right.
Slide #18 shows a portion of the Rand McNally Motor Carrier’s Road Atlas (MCRA) for the route in question. The MCRA is the standard truck atlas used by virtually every truck driver in the country.
Let me first explain a few things about routes.
There are three basic types of routes: designated routes, restricted routes, and everything else. At the top of slide #18, you can see a portion of the map legend, where it shows designated routes as being highlighted in yellow. A designated route means you can take a truck down it with no problem. Restricted routes are those that prohibit or restrict trucks in some fashion. There are many types of restrictions. The MCRA doesn’t show restrictions or low clearances on the map itself. To find these, you have to look at the table, as shown in slide #17. These tables are notoriously incomplete, particularly the low clearance section. Routes that are neither designated or restricted fall into the “everything else” category. The permitted use of these routes varies from state to state, and may include weight, length, or width restrictions, or some combination of these. Federal law provides access on these roads for a “minimum of 1 mile for food, fuel, rest, repairs, and to points of loading and unloading”. Access beyond the 1 mile limit depends on the particular state, and ranges from the Federal minimum of 1 mile, up to unlimited. In California, this means compliance with the “California Legal” limits, as earlier explained.
Referring again to slide #18, the route in question is not highlighted, meaning the “California Legal” limits are operative. Slide #9 further shows the 38 foot KPRA advisory.
In my years of driving, I learned early on, that when such advisory signs are posted in California, they aren’t kidding — not even a little bit. To me, any such advisory means pick another route, unless that’s the only way to get to wherever I’m going.
So, why would a truck want to use these routes in the first place? It really all comes down to money. Depending on where you’re coming from and going to, the use of these routes can save considerable time; either as a shorter route, or traffic avoidance. Generally, as long as it’s not a restricted route, it’s pretty much OK for a truck to use it. Most truck drivers will avoid these routes, commonly referred to as “goat paths” unless there’s a considerable advantage, especially with mountainous routes. Interstate highways generally have a maximum 6% grade (with a few exceptions), making it faster, easier, and safer for trucks to negotiate. Older highways have grades that can be much steeper — I’ve seen as much as 11% grades on such roads.
Now, let’s discuss trucks negotiating downgrades. A fully loaded truck weighs 80,000 pounds — that’s 40 tons. Remember your high school physics class? A truck that heavy at the top of a downgrade represents a lot of potential energy. Put the truck in neutral and roll down the hill, and by the time you hit bottom, you’d be going *really* fast. So, what needs to be done, is to dissipate this energy in a controlled fashion. Trucks do this by braking, turning this energy into heat, and dumping the heat into the atmosphere. Trucks do this by using engine compression brakes (known colloquially as “jake brakes”), and by using their service brakes. Engine compression brakes work by changing the valve timing of the engine, turning it into an air compressor. Compressing intake air heats it up, and then it’s released up the stacks. If you’ve ever gone down a grade near a truck, you’ve probably heard the noise from this.
Trucks also use their service brakes to slow down — and this is where brake loss can occur. Brakes can only reject just so much heat over time. Put more heat into the brakes faster than they can reject it, and they’ll start to heat up. As brakes start to heat, they begin to lose effectiveness (brake fade). Let them heat up enough, and they’ll lose all effectiveness, and can catch fire. This is why a heavy truck must go slow on long downgrades — to prevent this from happening. As the old saying goes, “you can go too slowly down a mountain all you want, but you can only go too fast once”.
The key to a safe descent in a truck is to pick the correct gear before descending. The rule of thumb is, “whatever gear you went up in, that’s the gear to go down in”. This works reasonably well in most situations. However, sometimes you’ll go up a hill, then run along the top for a while, or the downgrade will be much steeper than the upgrade was. This is why warning signs for grades are essential for trucks. These signs need to have the grade percentage, and length on them. Long stretches with multiple downgrades also need to be posted at the top, warning drivers, allowing them to execute the proper methods of negotiating the downgrades.
Most long descents aren’t all downgrades — there will be stretches of level, or even uphill road. If you take Donner Pass on I-80 as an example, there are dozens of signs advising trucks about the grades (both up and down) that they’ll encounter. A truck encountering a level stretch or an upgrade, is going to upshift to get back up to speed, if there’s no warning of further downgrades. Then, as the truck hits another stretch of downgrade, he’s suddenly in too high of a gear. This poses a serious problem, since the book says “Thou shalt not shift gears on a downgrade”. Attempting to shift on a downgrade, and missing the gear, leaves a truck in an uncontrolled descent — a runaway. It’s preferable to remain in gear, even if it’s too high.
Malia’s presentation didn’t show what downgrade warning signs were in place on the highway in question, so I can’t tell if they provided adequate warning or not.
The recommendations that Malia made in slides 41-45 are logical, reasonable, and would be effective if implemented. It’s important to allow trucks as much access as possible, to as many places as possible. Malia’s suggestions could be done relatively cheaply and quickly, and would be a good short-term solution. The proposed “High Desert Corridor” as illustrated on slide #37 would be a good long-term solution, and would have the added benefit of diverting some truck traffic away from Los Angeles.
Overall, Ms. Mailes did an excellent job with her presentation, and should be commended. It was logical and well thought out. The minor errors she made detract little from her overall presentation.
Comments and questions welcome.