By Ned Einstein
A few months ago, in “The Danger Deterrent” (National Bus Trader), I explored the unsettling dangers associated with vehicles with long wheelbases making left turns. In that article, I mentioned having served as an expert witness in likely two dozen or so left-turn-related lawsuits, yet have never been involved in a case involving a right turn. Superficially, one could only wonder why, since the “rock-and-rolling” necessary to turn right is far greater than that needed to turn left. Plus, most of the victims of left-turning accidents are visible directly through the windshield, often for several seconds before being struck by the nose of a bus or coach.
No reader should deduce from these comments that he or she need not be concerned about right turns, as a safety matter. They have their challenges. The most fascinating it that, other than turns into wide, multi-lane arterial streets or sweeping boulevards, right-turning vehicles with long wheelbases must necessarily spend a few seconds in at least one oncoming lane of the roadway into which they turn. These moments may more accurately be described as a pirouette than, perhaps, a dance step. And as a dance step, it may be more like a samba than a tango. But turning right into a “local” or “collector” street, and certainly any roadway with a single right lane, your vehicle will spend a few seconds dancing in the oncoming lane. So one must ask: Why so few collisions compared to the apparent ease of turning left?
Physics and Directional Stability
Almost every common motorist has, at one time of another, driven up or down a freeway ramp too fast, and experienced the sudden difficulty of keeping his or her car on the road while balancing this feat with the effort to avoid a rollover. Usually, and fortunately, one feels this sensation from the suspension system before one set of tires actually leave the pavement. But turning too quickly on a curve, and sensing the start of a possible rollover, is a scary moment. Is it a moment grounded in science.
In a nutshell, the sharper the arc of a turn, the lower the speed at which the vehicle’s outside tires will begin to leave the pavement, and the lower the speed at which the vehicle will actually roll over. There are plenty of sub-factors involved here: The vehicle’s center of gravity, tire conditions, type of suspension system and rolling resistance on the roadway surface are only among the most obvious. But the general principle remains true. And the degree to which wheelbase length factors into this dynamic is even more complex. Just the same, this reality helps explain why the first rule about turning left, in any vehicle, is to do it slowly. But the second rule is to not do it too sharply. Is it this second rule that creates the dance. This is because, once again, the defining constraint is the arc of the turn. If one wishes to turn faster, that turn must be wider.
Also keep in mind that, because the rear tires of a vehicle with a long wheelbase do not follow the path of the front tires in any proper turn (and much less so in a typically-tighter right turn), such a vehicle’s nose must almost necessarily take a dance-step or two into the oncoming lane. But the wider the turn, the more space this dance step take up in one or more oncoming lanes. And the more time the vehicle spends in this or these oncoming lanes.
Ironically, the driver of a large commercial vehicle cannot have it both ways:
- If this vehicle creeps around the turn like a disabled snail, and turns when its rear axle is at the optimum position with respect to the extended “near-side” curb-line, then the driver can minimize the space his or her vehicle occupies of an oncoming lane or two.
- At the same time, slowing to a crawl to minimize this space extends the time that vehicle must spend in this or these lanes.
Philosophers have debated concepts of time and space for centuries. Some have suggested that there is no such thing as time at all; it is merely the illusion of displacements in space. That “other Einstein” proved that as speed (i.e., the rate of an object’s movement through space) increases, time shrinks. In fact, at the square of the speed or light, time ceases to exist. Beyond this speed, time goes backwards — the best “underlying theory” any scientists have come up with to explain a “Black Hole.” Bus and coach drivers need not understand any of this. But they are dealing with a phenomenon every bit as complex during many of the right turns they make.
I do not recall right turns ever described in such terms in any operating manuals I have ever reviewed, even though most bus, coach and heavy-duty truck drivers almost certainly learn about these principles somehow. And most do not experience a rollover or two to get the point. With increasing experience, most drivers would naturally become better at striking a balance between turning speed and turning sharpness (or the arc of the turn). Yet this balance lies between two constraints:
- One cannot realistically creep around a corner, in a traffic stream, like a snail. At least not if one wants to avoid a few nasty honks from behind, and some minor risk of being rear-ended.
- At the same time, one cannot sweep across multiple oncoming lanes to create the arc needed to whip around the turn without rolling over.
These constraints necessarily force the driver of a long vehicle to strike some balance. As I have seen precious little written training about it, I can only conclude that bus, coach and heavy-duty truck drivers learn to strike this balance through experience.
Frankly, I think that learning to turn safely is one of the most difficult things a commercial driver must learn. So the typical six weeks of training many bus and coach drivers receive is hardly excessive. This particular maneuver is rendered all the more complex by the fact that not only do the arcs of turns vary considerably, but so too do speed limits. And while most vehicles would roll over while turning right at the speed limit, they often approach the turn at or near the speed limit — even though the industry standard is to slow down considerably, if not come to a complete stop before turning, even with a green traffic signal in the vehicle’s favor. Otherwise, mastering the nuances of turning is all the more important when one recognizes that a vehicle does not usually have the entire dance floor to itself.
Sharing the Dance Floor
One basic highway engineering tool used to control the dance floor (or the intersection) is the “limit line.” On roadways on which commercial vehicles operate, the limit lines behind each spoke of the intersection are often placed far enough behind to allow the nose of a turning bus, coach or large truck to rotate through the intersection-edge of the oncoming lane without striking an oncoming vehicle. Yet this tool only comes into play when vehicles are stopped at it — as they should when the intersection is controlled by a traffic signal or stop sign. (Rules for stopping at crosswalks actually vary from State to State; in some States, for example, one is only required to do so if a vehicle is parked at some point in the intersection.)
In contrast, when vehicles in an oncoming lane are not brought to a stop by one of these devices, signs or markings, the dance floor is wide open. During his rock-and-roll, a bus or coach driver need not merely “rock-and-roll” to make sure there is no pedestrian to be run over. And he or she need not merely align the rear axle, before turning, to avoid back-slapping or tail-swinging into a parked car. A commercial vehicle driver’s “rock-and-roll” must allow the driver to also peer a reasonable distance down the oncoming roadway to make sure that his or her vehicle does not share the same spot on the dance floor with an oncoming vehicle. (This is known as a collision.) Further, the higher the speed limit on the intersecting roadway, the further down this oncoming lane (or lanes) the commercial driver must see.
Rules of the Road
“Rules of the Road” is a common catchphrase or cliché sloppily employed to cover a range of procedures whose author was usually too lazy or inept to properly define. One often thinks of rules of the road as largely involving courtesies, like making eye-contact with fellow-drivers or -motorist, and perhaps “waving an oncoming or turning motorist on.” Sometimes, such rules are embodied in traffic codes, such as the principle like pedestrians have the right of way, or at an intersection, the vehicle to the right should be allowed to proceed first. I have always found this latter “rule” somewhat confusing — especially when a vehicle is poised at all four (or occasionally more) positions in the intersection. Then there is the rule, commonly embraced in traffic codes, that through-traffic should be allowed to proceed before turning traffic, unless directed otherwise by a traffic signal or Today’s rare live “traffic cop.”
So while there are at least some rudimentary rules that make sense in many common situations, the nuances of making turns (other than with respect to an oncoming vehicle not turning) rarely enter the broad, simplistic rules of the road. In sharp contrast, sharing the dance floor with an oncoming vehicle traveling toward an intersection from a perpendicular street is no simple matter.
Respect and Responsibility
In many previous NBT articles about “Safety and Liability,” I have opined that operating a full-size bus or motorcoach is, in many ways, as difficult as flying an aircraft. In stating this, it is fair to acknowledge that almost any idiot can be taught to lift off in an aircraft with minimal training. The challenge is landing it (as opposing to crash-landing it). In other ways, operating a bus or motorcoach is more difficult. One example is that pilots have little responsibility for passenger management, and since 9-1-1 (at least in theory), cockpit doors are even closed to passengers. So not only should there be no threats and no acts of violence, there should be no distractions.
As far as turning, I will admit that this seems more difficult for an airplane, particularly given the speeds at which they travel, and the balance they must maintain in order to not quickly fall into a dive. At the same time, the arc of a plane’s turn is exponentially wider than that of a ground vehicle turning on a roadway. Plus, if the pilot is capable, an aircraft can roll over multiple times with precious little risk (assuming this is done with the plane still in the air).
Regardless of whom is more deserving in this comparison (a pilot or a commercial driver), I have enormous respect to the skills of a good bus or coach driver. E-N-O-R-M-O-U-S. But to deserve this respect, that driver must take the responsibility to master the maneuvers described above.
In her popular recording “gone platinum” long ago, Aretha Frankly belted, “R-E-S-P-E-C-T. Tell you what it means to me.” What it means to me is, that to deserve my respect, a commercial driver must accept and embrace the responsibility of mastering the challenging skills noted above. If not, the most important rule-of-the-road should be: Stay off it.
The formula for the force of two colliding objects sloppily approximates the inverse square of their respective masses. So a 1000-lb. automobile colliding with a 40,000-lb. bus absorbs not 40-times the impact that the bus does, but closer to 1600 times that impact. When the loser in this match is made of skin and bones rather than steel, glass and rubber, these dynamics are greatly exaggerated. So the operators of such vehicles need be more than both skilled and careful. They need to be very skilled and very careful.
If a driver fails to master these skills, and/or fails to exhibit the degree of concern warranted — notwithstanding a third party compromising his or her ability to properly exercise these skills — he or she is going to lose my respect quickly. Far more importantly, he or she is likely to lose the respect of some jury, and along with it, the insurance carrier of that driver’s employer is likely going to open its wallet, and open it wide. While two steel vehicles colliding may often result in a mere fender bender, such vehicles do more than bend a fender when they strike a pedestrian. When a 43,000-lb. motorcoach does this, the affair rarely has a happy ending.