SLOW DOWN Dunn County: No matter who Pat talks to up here, the #1 complaint is always the same, i.e., the aggressive, reckless driving which routinely takes place on our roads.
By Dunn County ASA Pat Merriman
In fact, Stacey at the Herald just asked whether/not statistics or other data had been compiled about the most dangerous of these phenomena–the dreaded Passenger Vehicle versus Tractor/Sem-Trailer collision. Because, honestly, the MOST ridiculous (and deadly) driving up here is the professional big rig driver who is either just plain inconsiderate, in a hurry or poorly trained; and/or his/her counterpart the individual, private, passenger car driver who suffers from the same maladies. And, when this dynamic duo comes into contact… devastation!
First, at the outset, we are not taking sides about who is more at fault–the private driver or the professional driver. Each is equally at fault out there on the highway. However, our pet peeve–big rigs who are lumbering along on a 2-lane highway, running at far below the posted 65 mph speed limit (especially on steep grades) totally oblivious to the fact that several vehicles are trapped behind them. What ever happened to the old days when the driver would wait for a straight-away, pull over to the right and let traffic pass with a friendly waive and toot of the horn? On the flip side are these tail-gating knuckleheads in their private car, SUV (or, more often, dually pickup) tailgating, zipping past 3+ cars to pass everybody in front of them, usually in a no-passing zone, rolling through stop signs, and wreaking havoc to on-coming/merging traffic. What’s the hurry, brother? You can actually watch these dangerous knuckleheads, virtually every day, on 22 Hwy. flying up on that highway off a scoria side road (dust plume following) as they don’t even attempt to stop at the intersection, just, instead, screeching into traffic and, forcing approaching traffic to brake hard to avoid a collision.
But, again, the really moronic drivers (professional and otherwise) are those who engage in the foregoing games of “chicken” while driving the big, heavy semi (on the one hand) and the passenger vehicle (on the other). And, in researching the matter, frankly, all of these drivers need to be aware of some basic facts surrounding a big rig. And, the ignorant who cut them off, pull out in front of them, turn off of side roads into them, ad nauseum, really need to be aware of the same information because in the battle of big rig vs automobile/SUV/pickup truck, they are going to FEEL THE PAIN!
-STOPPING THE BIG RIG-
Simply put, again, we all have to abide by the laws of physics and when a passenger vehicle goes up against a big, fully-loaded semi-tractor big rig, the former is going to lose. The primary factor in braking distance for any moving object is inertia, i.e., the primary law of physics– the resistance of any physical object to any change in its state of motion, including changes to its speed and direction. It is the tendency of objects to keep moving in a straight line at constant velocity that creates the danger to the unwary (or impatient, reckless) driver who happens to be in the path of that big object. Remember, the big semi is going to continue moving forward until its momentum is absorbed (acted upon) by some intervening cause.
Why? Another basic principle of Sir Isaac Newton is that all objects resist changes in their state of motion but, the tendency of an object to resist changes in its state of motion varies with mass. The more inertia that an object has, the more mass that it has. And, a more massive object has a greater tendency to resist changes in its state of motion than a lighter object.
According to the National Highway Transportation Safety Administration (NHTSA), a fully loaded semi truck has the gross vehicle weight, depending on its cargo, of up to 80,000 pounds and, that’s 40 tons of mass. The average passenger vehicle weight is 4,000 pounds or 2 tons. Compare that to a 1,400 lb. cow running at 65 mph and mowing over a 2nd grade, Pop Warner player weighing-in at 70 lbs. and, you get some idea of how a 20:1 ration works when it comes to blunt force trauma at highway speeds. And, with water trucks hauling loads of liquid, some truly unfortunate phenomena also inure:
• Liquid surge results from movement of the liquid, particularly, in partially-filled tanks, in much the same way as an ocean wave and, we all know what a tsunami can do.
• When coming to a stop, the liquid will surge back and forth causing a wave inside the tank.
• When the wave hits the end of the tank, it tends to push the truck in the direction the wave is moving.
• If the truck is on a slippery surface such as ice/snow/rain, the wave can shove a stopped truck out into an intersection.
• Some liquid tanks are divided into several smaller tanks by bulkheads and, therefore, when loading/unloading the smaller tanks, the driver must not put too much weight on the front or rear of the vehicle or, hydraulics can create the same destabilizing wave effect.
• Liquids also expand as they warm and, therefore, a driver must leave room for the expanding liquid (“outage”).
• A full tank of dense liquid (such as some acids) may exceed legal weight limits causing the unsuspecting driver to have more mass and, thus, require even greater stopping distances.
• Even if weight is not an issue, caustic or explosive liquids create an additional risk in collision simply because of their nature and, therefore, greater caution must be used when hauling them to avoid a spill.
Improperly secured or placed loads are dangerous too. Because of the way they are designed, semi trucks have to conform to strict weight and load requirements on North Dakota highways. And, a common reason why big rig drivers lose control of their vehicles is because of an improperly secured load. When a load isn’t secured/loaded properly, its contents shift, and a sudden change in weight distribution can have drastic effects on steering, braking, turning or navigating, particularly in high winds. Loading a rig with too much weight on its front/back axle(s) can create instability and, therefore, driving a big rig is completely different that taking the family SUV or pickup for a spin.
At a speed of only 55 m.p.h., a semi truck’s stopping distance (even under optimal conditions) is at least 100 yards–the length of a football field and twice the distance required by a medium sized automobile traveling at the same speed. Why? Not only the foregoing basic laws of Newtonian Physics but, the braking system of a big rig itself comes into play. The compressed-air brake system of a semi truck is radically different than that of an automobile loaded with modern power-assist, caliper, hydraulic brakes. Air brakes have a lag time where nothing happens at all after the driver steps on the pedal, whereas, the brakes on my new Ford Explorer will put you through the windshield if you just touch them with the tip of your toe. So, if it even only took 1 second for the semi’s brakes to actually begin to slow the vehicle, that’s 1 second of travel (80+ feet at 55 mph, see, below) while the driver’s brain transmits the actual foot pressure so the system would just start its braking process. And, that doesn’t even consider the reflexes of a particular driver, i.e., the amount of time it takes for his/her brain to think about the need to apply the foot pressure in the first place.
n addition, semis still use drum brakes (as a rule) and, on hills or mountainous terrain, those drums expand, heat up and further reduce the truck’s ability to stop. And, even if the driver’s reflexes are so sharp that the vehicle travels that 100-yard stopping distance (at 55 mph, that’s 80.67 feet per second), you are going to get hit at 55 mph if you are within 85′ of that truck when it sees you and the driver reacts. And, that’s if the semi driver has the reflexes of Spider Man!
-STOPPING THE PASSENGER VEHICLE –
NHTSA also cautions that a second aggravating factor inures in our personal vehicles of which most of us are not even aware. A problem with a simple solution which, especially, exacerbates car vs semi collisions. In testing, NHTSA also found that correct tire pressure was a major factor in braking for a modern passenger vehicle. With under-inflation (below manufacturer’s suggested psi) increasing stopping distances and, of course, creating additional problems. Interesting facts as follows:
• 26% of passenger cars had at least one tire that is 25% or more under-inflated.
• 29% percent of light trucks (including SUV’s) had at least one tire that is 25% or more under-inflated.
• Of the foregoing passenger vehicles, automatic tire pressure warning systems (TPMS) did not necessarily notify the driver of this under-inflation problem.
• Vehicles that have existing TPMS tend to be more expensive luxury vehicles that are less common on our roads anyway.
• The average passenger vehicle loses 1% of tire pressure per month even under normal driving conditions.
Third, NHTSA’s results also indicated that the average passenger car would, on average, experience a stopping distance of 86.5 feet (29% of that required for a semi), while an SUV/light truck experiences an average stopping distance of 91.9 feet (30.6%). Thus, many drivers are apparently cutting off big rigs in the mistaken believe that they can interact with them in the same manner they do with their fellow passenger vehicle driver. OOPS! Further, although the vast majority of crashes would not have been prevented completely by small changes in stopping distance, they would (most certainly) have been lessened in severity based on the simple formula Force=Mass X velocity squared. Small increases in velocity more than offset large decreases in mass. In addition, NHTSA states that:
• 1.38% of braking passenger cars and 1.36% of braking passenger trucks could have avoided crashes altogether with proper tire inflation.
• The remaining 98.6% of passenger car, SUV and passenger truck crashes would still occur, but at a reduced impact speed.
PASSENGER VEHICLE DATA
Conventional Wisdom= Add 40% for avg. stopping distance for big rig.
Fourth, NHTSA notes that individual driver’s reflexes play an important role, “when drivers are faced with potential crash circumstances, they apply their brakes at a rate that reflects both their perceptions of the need to stop and the vehicles actual response to this need.” Some people’s reaction time is also, well, just slower and, even those of us with “quick reflexes” will all experience an increase in reaction time as we age. “Theoretically, braking systems should be capable of the needed response, if drivers apply it, up to a threshold at which the tires loose their friction capabilities.” And, if theories always worked (especially with anti-lock braking systems), crashes would never occur.
Regardless, NHTSA’s analysis indicated that 72% of fatalities and 54% of injuries that occurred on dry pavement happened in crashes with “skidding” occurred. Hence, why anti-lock braking is here to stay regardless as to the driver’s personal opinion about its effect on stopping distance. “Given the high level of skidding involved on dry pavement, this analysis assumes that all crashes that occur on wet pavement involve some level of skidding and thus would benefit from TPMS.”
-SNOW, ICE, & WATER-
Keep in mind, that the coefficient of friction for tires on dry pavement is around .7; on water, it’s .4; and, on snow/ice, it would be around .25. So, if one were traveling at 30 mph, stopping distance on dry pavement would be 40-42 feet for the passenger vehicle, +/- 70 feet in the rain and, +/ 100-120 feet on snow/ice. Quite an increase if you’re thinking about pulling out in front of that semi or slamming on your brakes, particularly, in inclement weather! And, for semi drivers, dry scoria/gravel has a coefficient of friction of .6 which is substantially less than pavement. The rule of thumb here is that a big rig is going to need approximately 40% more distance to stop than a passenger vehicle which, again, does not bode well for the latter (and other drivers in the vicinity) in a collision, particularly, in bad weather.
The American Trucking Association publishes the following defensive driving guidelines for motorists :
Never cut in front of a semi for any reason.
Be sure to maintain a distance of at least four car lengths when maneuvering in front of a semi.
Never linger alongside a semi because they have huge blind spots in which cars can disappear from the view of the truck driver.
The blind spot on the right hand side of the semi runs the length of the trailer and extends three lanes.
Pass on the left because the blind spots are smaller.
Keep a safe distance behind a semi truck–about 20 to 25 car lengths or, you are in the semi’s blind spot.
In addition, NHTSA warns professional semi drivers , after conducting extensive testing on tractors, trailers, electronic stability control (ESC), and roll stability control (RSC):
Crash data indicated that loss-of-control crashes were occurring with payloads as low as 5,000 lbs…A consequence of the physical size and mass of a tractor semi-trailer combination vehicle is less sensitivity to quick transitional (left-right or right-left) steering inputs… In 1979, the University of Michigan’s Transportation Research Institute (UMTRI) examined the yaw stability of a tractor semi-trailer during steering only maneuvers. The study found that tractor semi-trailer yaw instability was found at “elevated” levels of lateral acceleration in a steady-turn maneuver. Their results demonstrated that yaw instability can occur well below the rollover threshold for certain vehicles under the right conditions. UMTRI identified several factors that increase the likelihood of yaw instability with a loaded vehicle. These include… a high center of gravity location of the trailer payload… Other tractor-based design parameters found to degrade yaw instability included: low torsional stiffness of the frame, a short wheelbase, and a single drive axle…
According to FMCSA’s Large Truck and Bus Crash Facts 2008, the overall crash problem for tractor-trailer combination vehicles is approximately 181,000 crashes, 51,000 injuries, and 3,151 fatalities annually. Tractor-trailer combination vehicles are involved in about 74 percent of the fatal crashes involving large trucks, annually. These vehicles had a fatal crash involvement rate of 1.92 crashes per 100 million vehicle miles traveled (VMT) during 2008, whereas single unit trucks had a fatal crash involvement rate of 1.24 crashes per 100 million VMT. Combination vehicles represent about 25 percent of large trucks registered but travel 63 percent of the large truck miles, annually. Heavy-truck loss-of-control (LOC, also referred to as loss of directional stability, loss of yaw stability, jackknife, spinout, or plow) and rollover crashes are also a major cause of traffic tie-ups, resulting in millions of dollars of lost productivity and excess energy consumption each year…
Contributing Factors in Rollover and Loss-of-Control Crashes–Many factors related to heavy-vehicle operation, as well as factors related to roadway design and road surface properties, can cause heavy vehicles to become yaw unstable or to experience a rollover. Described below are several real-world situations where roll or yaw instabilities might occur and stability control systems may prevent or lessen the severity of crashes:
• Speed too high to negotiate a curve – Entry speed of vehicle is too high to safely negotiate a curve.
• Sudden steering maneuvers to avoid a crash.
• Loading conditions – Vehicle yaw due to over-steer is more likely to occur when a vehicle is in a lightly loaded condition and has a low center of gravity height.
• Heavy-vehicle rollovers are much more likely to occur when the vehicle is in a fully loaded condition as a result of a high center of gravity height.
• Cargo that is placed off-center in the trailer will result in the vehicle being less stable in one direction than the other.
• It is also possible that improperly secured cargo can shift while the vehicle is negotiating a curve, thereby reducing roll or yaw stability.
• Sloshing can occur in tankers transporting liquid bulk cargoes. This condition is of particular concern when the tank is partially full because the vehicle may experience significantly reduced roll stability during certain maneuvers.
• Road surface conditions – On a dry, high-friction asphalt or concrete surface, a tractor-trailer combination vehicle executing a severe turning maneuver is likely to experience a high lateral acceleration, which may lead to a rollover or LOC. A similar maneuver performed on a wet or slippery road surface may result in LOC.
• Road design configuration – Some drivers may misjudge the curvature of ramps and not brake sufficiently to negotiate the curve safely.
• This includes ramps with decreasing radius curves as well as curves and ramps with improper signage. A decrease in super-elevation (banking) at the end of a ramp where it merges with the roadway causes an increase in vehicle lateral acceleration (and may be accompanied by the driver accelerating in preparation to merge).
• Braking maneuvers – Most common heavy-vehicle LOC (jackknife) events occur due to rear wheel lockup during braking.
• Also, loss of steering control or “plow-out” can occur due to front wheel lockup, although this is most likely to happen on a heavy vehicle under light loading conditions and slippery road surfaces.
• Vehicle factors – Severely worn tires (tread depth below 2/32 inch) are more likely to contribute to vehicle spinout or plow out under wet slippery conditions.
• The condition of the vehicle’s brakes, including brake adjustment, is critical in enabling the driver to reduce speed for upcoming curves, and also to prevent brake fade from occurring on long downhill grades.
• Replacing tires that have insufficient tread depth and maintaining the ABS in proper operating condition are critical in preventing jackknife events and trailer swing during panic braking.
• Both RSC and ESC are enhancements to the ABS platform and for all of these systems to work properly, foundation brake systems and tires must be maintained in proper operating condition…
For speed limits that ranged from 0-35mph there were 3,966 crashes (again over a 5-year period, 2000 through 2004) related to LOC. For speed limits that ranged from 40 to 55 mph there were 11,387 crashes related to LOC. For speed limits over 55 mph there were 5,326 crashes related to LOC… Thirty-six fatalities were observed when the vehicles in crashes had payloads up to 5,000 lbs. The number of fatalities decreased to 24 when the vehicles had payloads between 5,001 and 20,000 lbs and increased to 100 fatalities for crashes in which the vehicles had a payload of more than 20,000 lbs.