Moving queues of stopped traffic on major expressways are a serious problem for public safety. Drivers who may travel for several hours at speeds of over 100 km/h develop the expectation that this free flow will continue into the immediate future. Maintaining a vigilance over several hours toward a seemingly unchanging condition may be performed by many drivers over many instances. However the high frequency of exposure over a life-time of driving means that eventually instances of inattention will occur. Of the thousands of drivers that travel on a segment of a major expressway every hour it only requires the inattention of a single driver to cause a major incident. This is particularly so when an unexpected incident causes a sudden stoppage of traffic and a queue begins to snake its way backwards towards approaching drivers who are not expecting that stoppage.
Lack of formal training in human behaviour causes many judgments to be made and misconceptions to be developed that fail to address the root problem. Those who could provide that insight are often not those posting their views on social media or given an opportunity to inform the public in formal news segments. Attention failures are not indicators of driver “stupidity” but are a demonstration of the reality that human performance has certain limitations because of the way we process information and respond to it. Though it is insufficient in its detail, it can be said that humans focus their attention on one item of information at a time and we are programmed to focus our attention on items that are seemingly of greater importance. Thus in most traffic instances, it is not that drivers are inattentive but rather they are attentive to other things besides what we, in hindsight, expect of them.
It is not that distant in time when similar problems of human behaviour have caused injuries and fatalities in various farm and industrial settings. Various stamping, crushing and cutting machines have been operated by humans who have sometimes become entangled in the machinery resulting their being stamped, crushed or cut apart. The obvious comment could be made that these operators simply had to stop placing their hands or clothing into the location of the machinery that would cause them to be entrapped and dragged into the moving machine. Such sage advice did not solve the problem. Instead various guards were put in place so that operators would not be placed in proximity to mechanisms that would capture them. Also various sensors were built into the machinery that would stop the operation of the machinery if an entrapment of the operator was sensed. This was the progress of technology that corrected the safety problems. While great effort may be expended via public education to the need to maintain vigilance on major expressways it is unlikely to make a large difference in increasing public safety. As in the past technological changes are needed.
One technology that could make a large difference is automatic emergency braking. Such systems do not require the driver to be attentive to traffic ahead in order to apply braking because the system is designed to detect stopped or slowing traffic that may not be in the driver’s view. Time is required before the such systems improve in their ability to deal with the full complexity of all real-life scenarios.
In the meantime some transportation agencies have attempted to develop technological systems on the highways themselves. As an example in 2011 the Texas Department of Transportation (TxDOT) developed a system of early warnings for queues of stopped traffic on approach to expressway construction sites. Portable speed sensors were erected to detect the speed of traffic as far back as 7.5 miles from the construction zone. Portable, changeable message signs were erected to warn drivers of the developing stoppage of traffic. Also portable rumble strips were laid across the lanes to create audible and tactile warnings. TxDOT indicated that their system reduced crashes by 45%. Such systems may not be a full solution for situations where a sudden stoppage occurs from emergency situations such as collisions. However they are an attempt in the proper direction of using technology to correct a serious, recurring safety problem that exists throughout modern expressways.
In the immediate area of southern Ontario, expressways such as Highways 400, 401, 402 and 403 carry a large percentage of heavy truck traffic. It is not uncommon to see trucks travelling very close to each other at highway speeds. As shown in the photo below, the view of these drivers is blocked by the wall created by the large dimensions of the trailers of the trucks ahead. Thus they are unable to detect the occurrence of emergencies that develop.
There is various research on heavy truck braking. One source comes from the U.S. Federal Highway Administration as shown below.
The table shown the next two photos provides data on the braking distances required by various heavy trucks from highway speeds.
The reported distances (in feet) do not include the perception-response delay that would occur as the driver detects, identifies and then commences a reaction to the incident. In some instances, such as a bob-tail (a road tractor minus its trailer), the braking distance can be over 500 feet or 150 metres. This is about the length of 1 and a half football fields.
There should be little wonder when, faced with a sudden requirement to brake such truck drivers are often the ones who collide into lighter, stopped vehicles ahead. Rather than singling these persons out as the cause of the highway problem, it is necessary to recognize the difference in exposure and address the root of the problem.
Increased percentages of heavy truck traffic is also a problem because of the inability to brake at the same level of efficiency as light vehicles.