Moving Over & Slowing Down Can Be More Dangerous Than Doing Nothing

It is apparent that basic information about the dangers of moving over and slowing down is being mis-reported leading to the potential of increased numbers and severity of collisions. In many instances initiation of braking and steering can be more dangerous than doing nothing at all.

In an OPP Twitter notification of a fatal collision that involved the death of a tow truck driver on Hwy 12 near Port Perry, Ontario on November 7, 2019 the issue of moving over and/or braking was discussed. In their description of the collision the OPP reminded motorists that they should “slow down and move over” when they see a tow truck or emergency vehicle with lights flashing”. A photo of the accident site was attached in the posting and it is reproduced below. It was not noted how the collision occurred and we must surmise this from the single photo.

Given the limited information it might best be explained that the red car was the original vehicle that came to rest in the ditch and the tow truck came to a stop next to it to pull it out of the ditch. The silver car in the distance was likely the second vehicle and the orange and blue cones likely identify the path of the tires of that vehicle before and after impact. No other photos were provided so the public can not determine what was located behind the camera and what might have prompted both vehicles to exit the roadway. There appears to be some damage to the left front corner of the red car which is not consistent with what would occur if it just slid off the road. So one possibility is that the silver car struck the left front corner of the red car and pushed it further into the ditch. But we don’t know. This is the type of guessing game that the public needs to conduct in order to obtain some idea of what actually happened. A crucial fact in all this is the condition of the roadway behind the camera.

Certainly there is snow on the roadsides and possibly this was a factor. We look at the background of the photo and see that the roadway is wet and not snow-covered. But then we do not know when this photo was taken in relation to the time of the crash or if road maintenance personnel drove through the site with salt and cleared the snow cover before the photo was taken.

We see snow on top of the tow truck. While we would expect to see the flashing lights on top of the cab of the truck we would also expect to see alternating flashing lights on at the back of the cab. Yet there appears to be snow covering two, small, circular areas where we would expect to see flashing lights. So were those flashing lights obscured by the snow?

And the overhead flashing light bar itself is not very prominent. So did that play a factor in the truck’s visibility?

Although the sky is essentially clear in the background we do not know the proximity of the collision time to when the photo was taken. The OPP indicated that the collision occurred in the morning but did it occur at 0100, 0600 or at 0800 hours. The visibility could involve total darkness, heavy snowfall or bright sunshine. We just don’t know.

Were there other vehicles indirectly involved? Was there a third or fourth vehicle that blocked the view of the driver of the silver car such that the tow truck was not visible until the last few seconds? If the driver of the silver car distracted, why was the driver so successful in avoiding contact with the tow truck and almost avoiding contact with the red car? Coincidence? Perhaps.

Looking at the final rest position of the silver car we know that it travelled a substantial distance after clearing the location of the two other vehicles. By considering some possible rates of deceleration we might arrive at an estimate of the vehicle’s speed. (By the way, the contact with the red car may have produced a “non-deployment” event on the silver car’s event data recorder and the police might have a precise speed at that impact). For argument’s sake, let us assume a post-impact travel distance of 40 metres with a deceleration value of 0.4 g resulting in an estimated impact speed of about 64 km/h. Judging that the vehicle would travel an additional distance from the centre of the lane up to the point of impact which might be at angle of 8 to 10 degrees we might consider an additional speed loss over that distance. This would provide an indication of the car’s speed when it began its motion toward the roadside. Using a computer simulation program we might study what kind of steering input, if any, might lead the vehicle to such a path. If a steering input was applied we might ask why the driver would do so, rather than steering away from the tow truck.

In earlier years, before electronic stability control, it was easy to detect when a loss-of-control took place because the vehicle would rotate about its vertical axis like a top. Invariably such a vehicle would reach a sideways angle approaching 90 degrees before the tires would dig in and the vehicle would begin to rollover. But here we appear to have two tire marks on the grass which suggest that the vehicle was travelling into impact leading with its front end, not sliding sideways and/or rotating. Yet, this could be a function of the electronic stability control, keeping the vehicle pointing straight ahead even through the vehicle is not under control of its driver. So the situation is more complicated without examining data from its event data recorder. Data that neither we, nor the public, can examine.

Newton’s First Law of Motion indicates that a vehicle will continue to travel along its original path until its motion is altered by an external, unbalanced force. What does that mean for collision avoidance? Braking and steering are unbalanced forces that act upon a vehicle at the interface of the tires and the surface on which it travels. On a smooth, dry, paved, highway surface our vehicle will travel along a straight road with only minimal inputs from the accelerator pedal (to nullify rolling and wind resistance) and a slight steering input to nullify the designed cross-slope (typically 2 percent) of the travel lane. In this condition we have (almost) the full tire force available to us when emergency actions are required. Thus we are in a stable situation.

When approaching a tow truck or other emergency vehicles stopped on a roadside we are required to steer away from those and apply our brakes to reduce our speed. These actions are not readily available on two-lane highways. They are more commonly discussed on multi-lane expressways such as Highway 401 and other 400-Series highway in Ontario. So we will consider this environment before returning to the example collision noted above.

Steering out of a lane and braking on a multi-lane expressway such as Highway 401 cannot be performed blindly and without forethought. Steering and braking have repercussions not only to the stability of our vehicle but also to the expectations of drivers around us. When the road surface is wet or slippery from snow, ice or other deposits on the road, the tire force can be reduced, sometimes to dangerously low levels. In those circumstances it can be dangerous to apply braking and steering without considering the consequences. Furthermore, often the tire force is not equal on all parts of the pavement. And the braking or steering force may also not be ideal due to conditions of a vehicle’s tires, suspension or weight distribution. These imbalances can cause an initial unintended vehicle motion that, through delayed attempts of correction, lead to a magnification of the problem. This inappropriate timing of corrections has been long known in loss-of-control collision causation.

Also steering into another lane cannot be done blindly and it takes time to look in one’s mirrors to assess if and when this can be done safely. Examination of lane changes by heavy trucks indicates that those changes need a time of 7 seconds or more, not including the perceptions needed by the driver to evaluate the need for a lane change. While smaller vehicles need less time for a lane change it, never-the-less, cannot be “done on a dime”. At 110 km/h a vehicle would travel about 30.5 metres every second or about 214 metres in 7 seconds.

In many instances the visibility of drivers ahead is not ideal. Some of this poor visibility is due to driver selection of a reduced following distance. But on a high volume highway such as the 401 almost everyone drives with inadequate following distance, otherwise, there would be vehicles continually steering into the gap and causing further reductions in that gap. So these gaps are not necessarily selected by the driver as they are a function of the driving environment. A further danger is that the Ontario government has mandated speed-limiting on heavy trucks and thus they travel at a much slower speed than the other traffic around them. This speed differential is the true cause of many highway safety problems as drivers of smaller vehicles attempt to weave around the larger, slower ones. In this process the large trucks act as mobile walls that prevent visibility ahead at many occasions when drivers are changing lanes. This is the factor that leads to many instances where drivers are not aware of stopped vehicles on the roadside even if they are emergency vehicles with flashing lights. When detection is made it is often done when a lane change cannot be done in safety and a dilemma occurs: Do I stay in the lane and take the chance of being charged, or do I attempt to make an unsafe lane change? In some instances of drivers who drive strictly according to the book, a dangerous lane change is made causing other drivers to take evasive action. This leads to collisions of other drivers while the “by the book” driver who causes the mess escapes detection.

In those instances where steering and/or braking may be dangerous, the option of doing nothing must also be considered. While this may create less than ideal results for exposed persons on the ground, it is a question of knowing what will achieve the best and safest outcome. Sometimes doing nothing is an act of a reckless driver while in other instances it is one of an experienced and safety-conscious driver who has properly considered the consequences.

The unfortunate result of the move-over law is that there are times when a driver has chosen the  correct action of doing nothing, and thus passing emergency vehicles without slowing or steering, yet that driver may be penalized simply for that observed fact.

Returning to the example of the fatal collision of the tow truck driver, steering out of the lane to avoid the tow truck could have been the cause of the second vehicle’s striking the tow truck driver and travelling into the ditch. This is common when substantial snow comes down but the temperature is high enough that the traffic is able to melt away the snow within the tire tracks of the lane. What remains is a set of tire tracks with bare but wet pavement. Outside of those tire tracks lies the unmelted snow that could be several inches deep depending on the specifics of the snow event. The available tire force is quite high on the wet pavement within the tire tracks, often in the range of 0.5 g. Conversely the area of the lane immediately adjacent  to the tire tracks, where several inches of snow may exist, may exhibit a force on that snow  that may be 0.2 g or sometimes lower. Compounding this problem is that a vehicle wandering out of the tire tracks, toward the centre-line, may experience the snow edge at only the left side tires. The real problem now reveals itself when a driver attempts to steer and brake while the left side tires are on the snow, where the tire force is substantially reduced, while the right side tires are on bare pavement. The difference in tire force creates a “moment” about the vehicle’s centre of gravity which results in rotation. Again this rotation is not necessarily immediate and final. We know from studying the tire tracks of such vehicles in severe, highway-speed loss-of-control collisions that there can be a series of adjustments made by the driver that are delayed in terms of when those adjustments are needed. So for example, when the rear end of vehicle rotates out the right the driver detects this at a delayed time and applies counter-steering just when that rear end is beginning to rotate back to the left and this increases the magnitude of the next rotation in  the opposite direction. This “fish-tailing” due to inappropriate steering and braking inputs eventually leads to a crisis where the vehicle rotation is beyond recovery. In newer vehicles Electronic Stability Control (ESC) steps in to reduce the wrongful effects caused by the driver by manipulating tire forces at each wheel to keep the vehicle pointing in the direction that it is travelling. But when tire forces are low and driver inappropriate driver inputs work against ESC there is a limit to what can be achieved and the vehicle exits the road surface, albeit pointing in the direction it is travelling, much like the silver vehicle’s path shown in the photo above.

The point of this discussion is that steering away and braking for stopped emergency vehicles and out of the regular travel path of a partially snow-covered road can lead to a disaster. Yet this is precisely what is being advised in the OPP discussion accompanying the photo. It is an example of the type of uninformed propaganda this is provided by persons who do not understand what dangers they are creating by making these broad generalizations.

What is essential in this discussion is a proper education of the public. Every day there are numerous serious and fatal collisions that could be used as examples to educate the public about what led to those tragic consequences. Those opportunities are missed because the details of police investigations are kept away from the public’s knowledge. Equally, the deep knowledge and experience that is essential to properly educate the public is also lost when police and news media do not possess that essential training and experience to educate the public.