The Steel Wave

The provision of school bus transportation is predicated on the notion that, below age 13, individuals do not fully possess the skills needed to cross streets and negotiate intersections. But this difficulty is further compounded by certain nuances of bus movement that few full-grown adults recognize, much less understand:

  • When the light turned green, a bicyclist watched a school bus pull forward into the intersection. Just before the bus’ front cap reached the halfway point – from which the driver would then have turned sharply to the right – the bicyclist assumed that the vehicle would be traveling straight through the intersection, and entered it alongside the bus. Because bicycles can accelerate more rapidly than buses, the cyclist reached the mid-point of the bus before the “steel wave” began moving back toward him. He and his bike were crushed by the curb-side rear tires.
  • Discharging his passengers at a rest stop, a motorcoach driver told them to return in 30 minutes and, turning right minutes later, pulled out toward the fueling station housed just around the corner. When a non-English-speaking passenger saw the bus pull out, she thought she was being stranded, and began to chase the bus as it accelerated. Running alongside and pounding it with her left fist, she actually caught up with the front plane of the coach and, momentarily, stepped in front of it. Of course, like most non-bus drivers, she did not realize that turning buses proceed straight only until their rear axles clear the extended curb lines alongside them. When the coach began turning back toward her, the steel wave knocked her down, and she was crushed by its curb-side, front tire.

Ink and Tread Marks

Were one to drive it over a huge stamp pad moments before turning right, the marks made by a bus’ rear tires would not coincide with those made by it front tires:

  • Because of its short wheelbase, the rear tires of an automobile would largely follow the path of its front tires, and the entire vehicle would appear to be turning in an arc.
  • In contrast, the front tires of a bus would advance forward most of its length (until the rear axle cleared the extended curb-line of the intersecting street), and then follow a parabolic path – first swinging to the right in an arc, and then reversing that arc as it straightens out in the new lane perpendicular to the one it just turned from. The rear tires do nothing of the sort: Instead, “dragged around” by the front, steering axle, the rear tires advance a few feet forward of the extended curb line of the intersection, then veer sharply to the right – taking a near-linear short-cut until they catch up with the linear path of the front tires further up the street where the bus’ trajectory begins to straighten out.

Viewed from above, these divergent paths might prove curious to a helicopter pilot (see Figure 1 below). But they lie far beyond the comprehension of most pedestrians, much less children under age 13. Watching the bus pull out into an intersection, most observers would think it was heading straight through. While someone knowledgeable about such things might wait for the bus to continue across the intersection, a child standing parallel to the bus near the front might begin to cross in the same direction as the bus when he or she notices the bus beginning to travel in a straight line. Only when it is too late, this crosser may discover these principles as the curb-side of the bus begins swinging back toward its new curb, and the bright yellow steel wall begins closing in on the pedestrian.

Conspicuity and Cuddling

Later installments of “The Crossing Guy” will explore a number of enhancements needed to improve school bus conspicuity. One of them is a curb-side beep-and-glow that engages and disengages with the right turn signal: When the bus’ right turn signal engages, these warnings need to remain engaged until the front axle begins to turn back to the left – when the second curve of the front tires’ parabolic path begins. But until such technology is in place, schoolchildren need to be taught to let a bus alongside them cruise through the intersection before they do.

I love Buster and Barney, and consider these resources underutilized by the pupil transportation community. But for my money, they are far too cuddly. When students touch the tires, I would like them to experience a low-voltage shock. When they touch the body, I would like it to be hot. But staying away from the body or tires is a relatively simple matter. Letting the bus go first when crossing alongside it is far more complex, and rendered even more difficult since those passengers crossing in front of it are taught to do so before it moves away.

The notions of parallel and perpendicular don’t appear in the math curriculum until early high school. By then, it is too late for an otherwise eager crosser. Despite the difficulty, letting the bus go first when moving alongside it is an important lesson young schoolchildren need to learn. Unless and until they do, they will continue to be at risk from the steel wave.

Publications: School Transportation News.