Have you ever found your company to be a defendant in a vehicle-pedestrian accident? If you have, you may remember an exchange like this between your driver and the plaintiff’s attorney:
Q: So, before you made the left turn, you were stopped at the light, correct?
Q: O.K. When you took off, how fast were you traveling during the turn?
A: Oh, about five miles per hour.
Q: And I assume that, you properly “covered your brake” during this turn, didn’t you?
A: Of course.
Five miles per hour! Covering your brakes? Are you crazy? No bus drivers turn that slowly, even when their training manuals instruct them to. And they do not “cover their brakes” when they just accelerated into a turn from a dead stop. Yet these are exactly the answers that almost every bus or motorcoach driver gives to these sucker questions. And then someone like me comes along, as the plaintiff’s expert, and my counsel then toasts the driver for his or her ignorance.
Along with my constant puzzlement about why drivers never seem to be taught anything about inertial and centrifugal forces, I am even more amazed that they are not taught about the difference between speed and acceleration. I am even more amazed that so few management officials seem to understand these concepts either. Perhaps if they did, fewer accidents would occur and fewer lawsuits would materialize to compound the damage.
Science for Simple Simon
Simon says, “A vehicle or any other moving object travels at some speed.” Unless this speed is constant, it speeds up and slows down along the way. When it speeds up, this is known as acceleration. When it slows down, it is known as deceleration. Stepping on the accelerator pedal will cause the vehicle to speed up. Removing it, and also depressing the brake pedal, will cause it to slow down.
Returning to our question-and-answer exchange above, it is obvious that a vehicle cannot jump from no speed to a high speed with nothing in between. So any change in speed necessarily requires the vehicle to accelerate or decelerate. That is why acceleration and deceleration are actually defined as a change in speed.
Finally, as far as impact forces go, force equals mass times acceleration (F =MA). It has nothing to do with speed. Nothing. Think back to all those grainy, black-and-white videos of space shuttle takeoffs from your childhood. Fifty feet above ground, in the Stage 1 rocket traveling at perhaps five miles per hour at that point, the camera shows the skin on the astronaut’s face practically peeling off. He looked more like a jackal than some Air Force hero. However an hour later, when the Stage III space capsule is traveling around the earth at 25,000 miles per hour, this same astronaut is floating around inside the capsule, drinking Tang. And he has returned to looking like just another Air Force officer.
This is also why, when your bus strikes a pedestrian from a constant speed of 25 miles per hour, the pedestrian usually gets hurt badly. After all, your bus represents a lot of mass striking a much smaller mass. Yet when your bus strikes that same person at 25 miles per hour while still accelerating, the pedestrian is usually mutilated. The cliché “speed kills” actually alluded to a narcotic. But the reference was obviously based on high-speed collisions. The point is: If speed kills, what does acceleration do?
I hope this explains why the answers to the dialog above are so profoundly inaccurate, why they are so naive, and why they sound so stupid. In case it is not obvious, the correct answer to the second question is:
A: Obviously I began my turn at zero mph. So at what point during that turn would you like me to estimate the top speed my vehicle had attained?
Similarly, the correct answer to the third question is:
A: I did not cover my brakes at all. I was accelerating from a dead stop. I did not even reach a speed where I needed to decelerate.
Given the wrong answers noted earlier, the plaintiff’s attorney (usually when someone like myself explains it to him or her) will have a field day with the rest of the driver’s deposition, and the defendant will usually lose the case no matter what else may have happened. Even in my limited experience doing perhaps a dozen (of more than 70) crossing cases where pedestrians were struck by left-turning buses, I estimate that these answers cost the collective defendants (or their insurance carriers) $20 or $30 million dollars. If the drivers knew the correct answers to these questions, they might have cost little or nothing. They certainly would have cost less. But far more importantly, if the drivers had actually understood the difference between speed and acceleration, many of these incidents would not even have happened.
Realistically, in all but a very sharp turn, acceleration should vary. In many cases, it makes sense (and according to some communities’ regulations) to require buses to come to a complete stop before making a turn. In others, particularly in rural areas with sweeping un-signalized curves, there is no harm in not stopping completely – although it is still important (a) to reduce speed approaching a turn, and since you do not have to accelerate from a dead stop (e.g., a red light or stop sign), (b) to cover your brakes.
Finally, there are reasons for accelerating differently at different points in a turn. At the start of it, when pedestrians, e.g., may be seen only through side windows, the corner of a windshield, or when the driver “rocks and rolls” to see around blind spots which exterior, rear-view mirrors, window posts, passenger-counting devices, and other objects might otherwise create, coming to a complete stop before turning is a good idea. Once the bus has turned, you also need to “clear your exterior, rearview mirrors to ensure that no pedestrian walks into the side of the bus (at the risk of being struck by the “steel wave” as the bus body turns, getting knocked down, and run over by the rear tires).
Otherwise, once the bus has nearly completed its turn, objects that might be struck can be seen directly through the windshield. So when all is clear in front of the bus and along both sides of it, it is important to get the tail of bus out of the intersection as quickly as possible. Then you can adjust to a normal travel speed for that roadway, under the proper conditions.
Finally, even on a motorcoach, scan your interior, rear-view mirror during the turn. You do not want someone approaching or returning from the rest room experiencing these inertial and centrifugal forces, much less while walking and balancing on part of one foot, rather than standing with both feet planted on the floor while holding onto a stanchion, as the standee on a transit bus usually would do.
Perspective and Perplexity
Let us start with perspective. This is only a magazine article. It does not remotely contain everything ever written about speed or acceleration. It does not even contain all the important aspects of speed and acceleration. It merely contains a handful of thoughts often misunderstood, but where such misunderstanding can lead to serious injuries and fatalities.
But these thoughts are also not complex. Anyone sloppily blurring them, or using them interchangeably, or focusing on speed when the issue is acceleration, should get a grip on these two simple concepts and the difference between them. Yet the public transportation field is awash with both drivers and management who fail to recognize, much less consider, the enormous distinction between them.
These distinctions are also not rocket science. But even in rocket science, it is important to not mix up basic principles. F=MA should not be confused with E=MC2. Sorry. That was the other Einstein. But even this concept is not confusing when coherently explained. It simply states that energy is equal to an object’s mass multiplied time the square of the speed of light.
Now, the square of the speed of light – crudely 186,000 miles per second times 186,000 miles per second – is 34,596,000,000 miles per second. Pretty darn fast. But what it means, while a startling finding, is actually quite simple – although hard to envision since the fastest things we have ever seen move compared to such speeds are, perhaps, dead snails. In my childhood, a “speeding bullet” travelled only about 1,100 feet per second. The speed of sound, in fact, is only 1,126 feet per second (known as “Mach 1” when the first aircraft “broke the sound barrier”). So we have had no real-life experiences that have prepared us to sense what this equation means.
But what it means is that, as an object approaches such a speed, time slows down. At this speed, time stops. Beyond this speed, time actually reverses. This was proven mathematically almost 110 years ago. And this is the essential principal that makes space travel between distant solar systems possible where the astronauts will still be alive (in theory, possibly even younger) when they reach their destinations. Outside of mathematics, of course, this may never happen: The fastest thing to travel that we know about – light – travels at only 1/186,000th of the speed necessary for this to happen. It would take an almost inconceivable leap in technology to create something that could travel at the speed needed to alter time. But mathematics do not lie.
So now you can tell your friends you understand the theory of relativity. Because you do. There is not much more to be said about it, or anything more most Earthlings ever need to know about it. But now that you understand one of the most important principles in all of physics, you have no excuse for not understanding the difference between speed and acceleration. This is like playing with crayons. Yet in lawsuit after lawsuit, I constantly come across clever and ignorant attorneys alike asking drivers and transportation managers about the proper “turning speed” from a dead stop at a red light – and getting the ridiculous answers noted above.
Life Beyond Crayons
The few examples noted above, where the difference between speed and acceleration may have been blurry, are just rudimentary examples. Thinking further about them, it is possible to develop more advanced and more usable ways of applying these concepts to vehicle movement and vehicle safety. As noted, one approach might be to think about modifying acceleration to optimize what may mistakenly be thought of as opposite goals: Cautiously looking for and observing things around and in front of your bus during a turn while also getting the tail of the bus out of the intersection as quickly as possible. This would appear to require a mastery of some variation in acceleration, and the application of that mastery would necessarily vary not only with the radius of the turn, but with respect to other objects the driver encounters or sees during the turn.
So while it may take awhile for such nuances to become “industry standards,” you will not have to rely on them nearly as much in court if you think about these concepts coherently, apply them to your training and your driving, and express them articulately in court – if it comes to that. It usually will not come to that since, if you think and act clearly about acceleration and the things you should do while your vehicle is accomplishing it, you will rarely find yourself as a defendant in a lawsuit.
Now go home, and tonight at dinner, tell your kids that you understand all about the theory of relatively. And teach it to any of them beyond the third grade, where they were taught about multiplication. You should have no trouble replicating the explanation you just learned about this above, and should remember this pretty easily. Save the simple stuff for your job.
Eliminating vehicle-pedestrian accidents is a worthy goal, even if it is an impossible one for an entire society to reach (even though Sweden is getting close). So you will not fail if you do not reach this goal. But you will absolutely fail if you do not use the knowledge at your disposal to try.
The opinions expressed in this article are that of the author and do not necessarily represent the opinions of NATIONAL BUS TRADER, Inc. or its staff and management.