While school buses are generally safe for transporting thousands of students each day in Ontario, they have their vulnerabilities. Many drivers of passenger cars have noted that even when they do not apply much pressure to adjust their steering wheel their vehicle continues to maintain a straight line path. That is not the case with school buses.
Bus drivers must maintain a continual lookout for deviations in a school bus path because even a momentary lapse can cause the bus to veer out of a lane. This problem is more important at highway speeds and when school buses must frequently travel on lower volume roads which are narrower. Furthermore many of these low volume roads may contain a hard surface but the surface is a tar and chip variety which frequently contains bumps and depressions, more so than an asphalt paved surfaces.
On gravel roadways school buses have a further disadvantage because of their wider track width. If one looks at a typical gravel road one will find that there are typically three channels of beaten down or bare surface. These are caused when light duty vehicles use the centre of the road thus the driver’s side wheels follow the same path regardless of whether a vehicle is travelling one direction or the other. But larger vehicles such as school buses cannot fit into these channels and inevitably the right side wheels of a bus end up travelling on the less beaten down and loose gravel that is outside of these channels. What may not be appreciated is that loose gravel contains a lower co-efficient of friction than hard-packed or bare gravel. This difference in the co-efficient of friction is what can cause different tire forces on the right versus the left of the bus centre-of-gravity. Such differences in tire force is what causes “yaw” or rotation and thus loss of control.
The combination of these facts makes it important that bus drivers maintain a constant lookout whenever travelling at highway speeds along back roads. Because of school bus driver shortages there are occasions when inexperienced drivers end up driving along a back road at highway speed without appreciating what dangers exist.