All vehicles on the road are equal but some are less equal than others, not least because fully loaded heavy trucks often can’t stop safely in time
Let’s kick off with a fact – heavily laden articulated trucks are generally unable to come to a complete halt in the time it takes a yellow traffic light to turn red.
Now, ever heard of the ‘dilemma zone’? You will know it, even if you don’t know its name.
Imagine you drive a heavy-duty truck, or you employ one who does. Imagine an experienced driver operating a fully-loaded semi is approaching traffic lights, in this case in a 60km/h speed limit zone.
The driver understands the dynamics of the vehicle very well indeed. And when the traffic light begins to turn yellow, or amber if you prefer, the idea of an emergency stop, with the load of steel being hauled, is judged to be just too dangerous.
It all happens in a sliver of a split second as the driver makes the decision in that dilemma zone mentioned above. Brake very hard and risk jack-knifing in the traffic, or continue through and risk a hefty fine.
Professional driver Don Smith from New South Wales got that hefty fine, along with the red-light camera image of the infraction, but felt aggrieved.
“But what could I do?” he said to his father, Brian Smith, a western NSW farmer. “There just wasn’t time to stop safely.”
And so began a quest to finds out why yellow lights in flat 60km/h-limit roads are set at four seconds, when all evidence is that fully laden combinations are unable to manage to stop in time.
This writer can attest that even the most inadvertent red-light infringement will fail an appeal to the authorities and legal advice tends to be not to bother unless there was a life-or-death level of situation. Granted, many are tempted to ‘try it on’ but in neither case was that the ambition.
Indeed, quite separately from this exercise, it is a public concern for heavy-duty truck drivers and, given the penalties by way of licence points, can be for trucking companies seeking to keep their drivers on the road as well.
Without mentioning yellow lights per se, professional driver Dale Compton, in a submission to the Glenn Sterle-led Senate trucking inquiry, made it plain when calling for the use of advanced technology for traffic lights.
“We need better traffic lights that are aware of a heavy vehicle approaching and keep it green,” Compton writes.
“Momentum in a truck is everything, braking hard for a red could be life threatening.”
PLEA FOR UNDERSTANDING
Like this writer once did, and because Don was on the road so much of the time, Brian sought to bring an argument of mitigation to the authorities in New South Wales.
“The lights turned yellow, and it was decided that there was insufficient distance before the lights to make a controlled, stable and safe stop before the lights, so a decision was made to continue through the lights,” Brian wrote.
“This decision was based on experience gained driving heavy vehicles of all different combinations from triple road trains to single trailer combinations in every mainland state in Australia, covering several million kilometres, over a period of 20 years.”
Brian pointed out that the photo was taken 0.5 seconds after the red light appeared and 5.1 meters of the vehicle was over the stop line at that instant.
His calculation is that, at a speed of 60km/h, any object covers a distance of 66.66 metres in four seconds, and 16.66 metres in one second.
The front of Don’s truck crossed the stop line about 0.194 seconds after the red light, and that it was 3.23 metres over the stop line when the red light illuminated.
At the time the yellow light first came on, the front of the offending vehicle was most likely 63.43 metres from the stop line, given a speed of 60km/h, and had about 3.806 seconds in which to stop before the stop line.
So, is it reasonable to expect any fully-loaded rig to stop in time in such circumstances?
Brian set to work on research in an effort later replicated by ATN. He found himself reading a 2004 study by consultancy Roaduser Systems into heavy vehicle stopping distances in Australia.
It had been commissioned by Main Roads WA and used in a ‘Submission to the Parliament of Victoria’s Road Safety Committee Vehicle Safety Enquiry’, involving a study of ‘Acceleration and deceleration testing of combination vehicles’.
This was a national project, “the results of which are being fed into the Review of Austroads road design guides, and the Australian Level Crossing. Assessment Model for sight distances required for Heavy Vehicles at Railway Level Crossings”.
If so, there is precious little evidence of it being taken into account at Austroads beyond rail crossings.
Based on repeated testing, it found livestock semi-trailer average stopping distance, including reaction time, was 109 metres, reflecting the need to avoid injury to animals – for an end tipper semi-trailer, that was 84 metres and the same for a B-double freight combination.
That is a lot more than the 66.66 metres in four seconds that the yellow-light timing dictates in 60km/h zones.
ALL ROADS LEAD TO AUSTROADS
The questions now arise: how did we get here and what, if any, appreciation for safe braking and the differing dynamics of laden heavy vehicles was allowed in the decision to make yellow light duration at 60km/h four seconds?
Well, in a federation where states often fail to see the value of national guidelines, federal roads body Austroads has, to its credit, managed to convince several of road authorities, including in Auckland, New Zealand, to accept its Guide to Traffic Management.
Part 9 of the guide, Traffic Operations, which notes that yellow light intervals need to be longer if speed limits are higher or roads sloping down and shorter if the obverse is true, covers traffic light duration and starts promisingly enough.
“The purpose of the yellow interval is to provide sufficient warning of the termination of the phase,” it states.
“A driver must stop for a yellow display provided it can be done safely.”
But from there, trucks are only mentioned in passing in relation to their inferior braking performance compared to cars.
“Another important consideration is the perceived danger of a rear-end collision with a following vehicle (particularly a heavy vehicle), which may not be prepared for the sudden deceleration,” it says.
Working against any softer view on duration is the concern, backed up by 60-year-old US research, that that there may be dangers.
“If the yellow interval is too short, vehicles within a certain distance from the stop line will be unable (or unwilling) to stop before the red signal appears, and if the yellow time is too long, motorists will tend to abuse the signal,” the guide states.
“As Gazis et al. (1960) have shown, an inappropriate choice of yellow time can place an approaching driver, at the onset of the yellow signal, in the predicament of being too close to the intersection to stop safely and comfortably, and yet be too far from it to clear the conflict area or even reach the stop line before the red signal appears.”
Also of note is that the deceleration rate Austroads and the state roads authorities rely on, is 3.0m/s2 and “is dictated by the needs of the driver who requires the maximum deceleration acceptable to the majority of the population (say 85%)”.
There is no indication heavy-duty trucks are within that percentage figure and it is safe to assume none are.
RED-LIGHT RUNNING
Possibly the most relevant academic or any other study to the issue at hand is found in a US publication, the Journal of Transportation Engineering, though it is focused on vehicle-actuated traffic signals.
It’s called ‘Signal treatments to reduce the likelihood of heavy vehicle crashes at intersections: microsimulation modeling approach’.
As it happens, this is an Australian study done in 2008 by research fellow Jeffrey Archer and professor William Young from Victoria’s Monash University and, as the title says, it uses simulations.
It notes that, in an unnamed and possibly generic metropolitan area studied, 16 fatal and 203 serious injury crashes occurred between 2002 and 2008 at vehicle actuated signal-controlled intersections compared with a total of 68 fatal and 3,500 serious injury crashes for all vehicle types.
However, it was not possible to determine how many were the result of red-light running.
The report does note that, according to “the literature, a typical level of hard heavy vehicle braking is 4.5g, for lighter vehicles, such as cars, a corresponding value was 0.70g [National Road Transport Commission (NRTC) 2003].”
Though the focus was on an 80km/h zone rather than 60km/h, it says: “The best overall safety effect was found for the straight forward increase in amber time duration from 4.5 to 5.5 [seconds].
“This gave an average of 69% red-light violations and a 72% reduction in the number of post-encroachments.”
But the conclusions state this is likely a short-term fix.
“This solution is, however, known to be subject to behavioural adaptation, which significantly reduces the overall impact in the medium to long term,” the report says.
“Furthermore, allowing additional unutilised amber on each signal cycle is inefficient from a traffic performance perspective.”
The researchers, noting further research is required, instead advocate two other vehicle-actuated signal treatments:
• extend green time for heavy vehicles caught in the dilemma zone before the change to yellow/amber
• a suitable extension of all-red when a vehicle is deemed to have a high probability for red-light running during the amber or all-red phase duration.
WHO CARES?
Well, apart from those caught out, or destined to be, by what appears in practice to be unfair system of strict liability, gaining acknowledgement from authorities that there may be a problem, in ATN’s experience, falls foul of the bureaucracy’s protective instincts.
While Brian’s heroic individual efforts to find out how we got here gained some help from a couple of regional officials and a basic reply from a minister’s office promising to take his concerns to Austroads, repeated journalistic questioning under control or advice of both Transport for NSW and Austroads – and by extension, of the nation’s other road authorities – resulted in significant failures to address the central issues.
These issues were, whether:
• truck braking dynamics were ignored at both levels when setting yellow/amber light durations
• truck drivers trying to do the safe thing are being unfairly penalised for ‘red-light running’
• authorities are going to do anything about what appears an unconscionable situation akin to the refusal in any reasonable manner to provide proper truck stops for fatigued truck drivers.
Austroads did manage to get about half its member authorities to say that they followed its guidelines on yellow light durations, but little more than that.
Read Austroads’ research on traffic flow anomalies, here
Interestingly, there was a hiatus of several weeks between ATN’s approach to Austroads and the appearance of a new set of modelling and measures for heavy vehicles.
When it came, Austroads advised on yellow light duration in a written statement: “The yellow timing is determined by a combination of the driver’s reaction time, the design speed, the deceleration of the vehicle and the approach grade over the stopping distance.
“The complexity of the calculation and the potential impact on delay (for all road users) and safety means it would be unlikely that a traffic engineer would consider simply adding a second on to the timing.
“The impact of an additional second can be significant in terms of traffic flow and driver behaviour.”
On what consideration of heavy vehicles and traffic lights has been taken, there was a chink of light.
“A review of acceleration and deceleration characteristics for heavy vehicles has been undertaken from the point of view of traffic modelling as part of a recent Austroads project (AP-R609-19 Improving the reliability of heavy vehicle parameters to support more accurate traffic modelling in Australia and New Zealand).
“The resulting guidance will be considered for update into the Austroads Guide to Traffic Management.
“Green extension, early start, coordinating signal offsets, bypass lanes on signalised motorway entry ramps, and Advance Yellow Warning Flashing Signs (located in advance of the traffic signals and activated before the onset of the amber phase to give heavy vehicle drivers more advance warning of the impending change from green to amber) can all assist heavy vehicle movements.
“These treatments were detailed in Signal Management Techniques to Support Network Operations published by Austroads in 2015.”
It should be noted that an Austroads project on ‘Improving the reliability of heavy vehicle parameters’ for modelling – a document that has no focus on traffic light behaviour apart from when they turn green but does look at all other behaviours – states maximum deceleration measured as metres per second squared (m/s2) is put at 3.0 for B-doubles and semis and 2.75–2.85 for double road trains.
Maximum deceleration for cars is put at 6.0.
So, there is no mystery on the differing braking dynamics between trucks and cars in Austroads thinking. The mystery continues to reside in what will be done about it, especially as the five items it says “can all assist heavy vehicle movements” are yet to be a common feature on our roads.
ACROSS THE POND: HOW THE AMERICANS SEE IT
Given the dreadful toll automobiles big and small have taken on drivers and pedestrians, there can be little surprise that the focus of researchers are on causes and ways to avoid fatalities.
That holds for here as well as overseas, where local researchers go to access a great breadth of knowledge, as the Austroads mention of the Gazidis study (page 55), old though it is, underlines.
So, it is possible to find ‘Guidelines for timing yellow and red intervals at signalized intersections’, prepared for the US National Cooperative Highway Research Program (NCHRP) Transportation Research Board of The National Academies.
It must be said there is little, if any, mention of trucks here either but it does tackle yellow light periods.
“At intersection approaches where yellow signal timing duration is set below values associated with ITE [the US’s Institute of Transportation Engineers] guidelines or similar kinematic-based formulae, increasing yellow change interval duration to achieve ITE guidelines can significantly reduce red-light running,” it states.
Six studies are mentioned and it was “found that increasing yellow change interval duration by about one second at approaches deemed to have insufficient change interval timing was associated with reductions in red-light running ranging from about 36 to 90 per cent.
“This range includes a number of weak study designs. The best estimate of effect on red-light running, based on better designed studies, is about 36 to 50 per cent reduction.
“Likewise, increasing yellow change and/or red clearance interval timing to achieve values associated with ITE guidelines or similar
kinematic-based formulae can significantly reduce late exits, as well as conservatively-defined potential vehicle conflicts.
“Evidence generally shows that increasing the duration of red intervals does not increase red-light running.”
Though one study concluded excessively long yellow change intervals “definitely are hazardous”, though another of those six studies finds this is so only after 5.5 seconds.
The upshot was:
• using the current ITE guidelines to calculate the duration of yellow change and red clearance intervals has been shown to reduce total crashes 8–14 per cent while reducing injury crashes by about 12 per cent
• increasing the yellow change interval to the duration calculated by current ITE guidelines has been shown to reduce red-light running occurrences 36–50 per cent. Increasing the red clearance interval to the duration calculated by current ITE guidelines has not shown to increase red-light running events; however, the crash results associated with installing red clearance intervals at locations previously without are unclear.