Hwy 401 – What is More Dangerous Speed or Difference In Speed?

High speed can be dangerous, but is it more dangerous than a difference in speed? That is one of the questions that can be explored through the analysis of traffic motions on major expressways such as Highway 401 in southern Ontario.

Observations by Gorski Consulting this fall have explored the speed and difference in speed of traffic along Highway 401 in southwestern Ontario. Observations by Gorski Consulting indicate that this expressway may carry anywhere between 42 and 48 percent of heavy truck traffic such as 18-wheeler tractor-trailers, truck trains and intercity buses. The Province of Ontario has created legislation that has reduced the maximum capable speed of heavy trucks to about 105 km/h. Observations by Gorski Consulting confirm that indeed almost all heavy trucks travel along Highway 401 at about 105 km/h. There is a conflict however when these large, slow-moving vehicles interact with much faster traffic that may be difficult for truck drivers to see and can accelerate out of blind spots into locations that truck drivers do not expect.

Observations by Gorski Consulting were taken of traffic at one location just west of London, Ontario in the median lane of Highway 401. The median lane is the one closest to the centre median and is generally understood to carry the fastest-moving traffic.  When all the traffic is considered the average speed of vehicles in the median lane was 115.9 km/h. However this lane was also populated by a number of slow-moving, heavy trucks. When the speed of those heavy trucks is removed from the data we are left with an average speed of 118.0 km/h. One might wonder what the average speed of non-trucks would be if those heavy trucks were not present.

It is not an accident that policy-makers in the Province made this decision to limit the speed of heavy trucks. They likely observed that mixing these “moving barriers” with unacceptably fast-moving traffic would create exactly what has been observed: the heavy trucks cause the speed of other vehicles to become slower. A further complication exists which explains the additional importance of using these moving barriers for speed control. It is that stopping speeders on this very busy highway is very dangerous for police.

Although legislation was introduced (“The Move Over Law”) requiring motorists to slow down and steer away from stopped emergency vehicles this may not be as safe as expected. Vehicles travelling at a constant speed without lane changes reduces the number of conflicts that lead to crashes. Requiring drivers to make lane changes and speed changes creates the conflicts that lead to crashes. This is not a good idea in the vicinity of vulnerable emergency personnel who cannot always keep an eye out for every vehicle that passes by. Thus the well-intended law may make the safety problem worse. Thus using heavy trucks to control traffic rather than placing police in dangerous situations makes some sense. Yet this decision does not come without some drawbacks.

The difference in speed of heavy trucks and other traffic creates its own conflicts. Drivers of non-truck vehicles who are rarely controlled by police end up travelling at unusually high speeds. When they catch up to slow-moving heavy trucks they can slow down rapidly and/or change lanes. These quick actions cannot be detected very well by truck drivers whose ability to avoid conflicts is already limited by their inability to change speeds or change lanes. These conflicts may be the origins of many collisions but are difficult to detect because there is no physical evidence left of these conflicts. Thus it becomes important to study vehicle motions along Highway 401 to capture those near-miss incidents that cannot be captured through standard police reports from collision investigations.

Gorski Consulting continues this work. There will be further reports made in the near future about the findings gathered from these studies.