Revised 7 April 1998.
The Symposium brought together regulators, manufacturers, researchers/consultants, operators and drivers from around the world. It covered a wide range of issues connected with heavy vehicle operations - not just "weights and dimensions". Conference proceedings are available on CD ROM from IFRTT (updated link pending).
The effects of government budget cuts were evident - there were very few representatives from overseas government organisations but several papers were presented on behalf of regulators who couldn't make it to the Symposium.
These notes are my personal observations about some of the many topics covered at the conference. The notes are very biased towards topics that interest me!
Performance standards for vehicle dynamics
Many authors presented papers on the evaluation of the dynamics of heavy vehicles. Most of these built on previous research on issues such as roll stability, yaw stability (eg rearward amplification), road space requirements, swept paths, lateral road transfer ratios and gradability.
Additional "performance measures" were proposed by several authors. Boudewijn Hoogvelt from TNO and Hans Huijbers from the Netherlands Ministry of Transport, presented a paper on a pilot study of longer, heavier articulated vehicles. Their evaluation included an innovative way of assessing the effectiveness of the driver's mirrors for viewing critical points on the vehicle during a turn. Also covered were overtaking considerations, time to clear an intersection, cross-wind effects and the consequences of multi-vehicle pile ups on motorways. The MADYMO modelling for the latter evaluation was rather dramatic. It is a valid research question but I do not think the media or public is ready for a "performance measure" that, in effect, estimates the number of cars crushed when a heavy vehicle runs into the back of a queue of cars!
Computer simulations of heavy vehicle dynamics
It is evident that computer simulations of various dynamic situations agree well with experiments on real vehicles. Researchers are able to evaluate the dynamic behaviour of complete vehicle systems (ie combinations) against performance targets such as those mentioned above. I am not confident, however, that we will reach the stage where these sophisticated packages can be used for direct regulatory control of vehicle performance. One problem in Australia is that the regulations tend to apply to individual components of a combination but the dynamic performance also depends on the way that these components are combined (this has been a long-standing problem with braking regulations). I believe the packages are essential tools to enable highly qualified personnel to determine whether innovative vehicle configurations meet the intention of the vehicle regulations (more on this below). These experts can then assist in the preparation of a specification for construction of the vehicle and a submission to the registering authority. An extract from the specification could then be carried on the vehicle to aid in vehicle operations (eg coupling the correct trailers) and on-road enforcement.
One extension of the computer simulations that I would like to see is determination of the rate of onset of instability such as rollover or trailer sway. For example, the benefits of having good roll stability are diminished if the onset of roll is so sudden that the driver gets no warning. The presentation "Heavy truck size and weight safety" by Chris Winkler (UMTRI) described a study which measured the lateral accelerations of hundreds of vehicles in service. This study found that there is a wide range of rollover thresholds and that drivers tend to adjust their driving to these thresholds (in effect, the total time spent near the roll threshold of the vehicle totalled several minutes per year). Perhaps a roll warning system is just as important as roll performance so that the first time that drivers get near the limit they are alerted and can adjust their driving to suit (Rod George from ARRB advises that there are some difficulties balancing sufficient warning against false alarms with these devices).
Highway bends and long combination vehicles
An area that requires further investigation is the ability of long combination vehicles to negotiate bends on highways. At very low speeds the cut-in of the last axle groups tends to increase ("centrifugal" forces and other effects tend to reduce the cut-in at higher speeds). This means that a very long combination might not be able to stay within its lane if it is forced to negotiate a turn at low speed. A further problem, which was mentioned by several presenters, is that considerable "drag" forces can accumulate from the trailer tyres when the combination travels around a bend (another contributing factor might be the angular difference between the direction of the last trailer and the direction of the hauling vehicle: proportionately more traction forces must be generated in order to overcome the drag). This, effect, combined with the extra tyre scrub at low speed, means there is the risk that a large combination will stall if forced to negotiate a corner at low speed. And there might be insufficient traction to get the combination started again.
The possible need to enter a bend at a minimum speed raises obvious safety concerns!
Inclusion of principles in vehicle standards
One way to introduce more flexibility into the vehicle standards is to include in these standards (which might be regulations or guidelines) a clear statement of the principles that they are intended to address. I am involved, on a voluntary basis, with an innovative approach to town planning in the local government area of Warringah near Sydney (see "Draft LEP"). Traditional town planning building controls are grossly over-regulated and yet the results are usually a mess - certainly not what the regulators had intended. Warringah is taking the radical approach of including a "statement of desired character" in the regulations, together with general principles such a sharing of views, quality of rainwater runoff and the like. In this way building inspectors, builders, architects and Land and Environment Court assessors will have a clear indication of the type of buildings that the community prefers in a given location.
One of the problems with current vehicle standards is that the intention is implied (safety, network efficiency, environment etc) but is not actually stated. Therefore every time that an innovative "non complying" vehicle is proposed to the regulators they have to make value judgements about the degree to which prescribed requirements can be varied. Such judgements will always need to made but a statement of principles would provide much clearer guidance for the decision makers.
The one-to-one trailer/truck mass ratio which applies in Australia (see Rod George's paper "The dynamics of truck trailer combinations") is a classic example of an arbitrary prescribed standard which is design restrictive. This ratio appears to have been introduced many decades ago and the reasons for this particular value are now lost. If a statement of principles which describes a well-behaving, controllable truck trailer combination had been included in the original regulation then subsequent regulators could have allowed exemption from the prescribed mass ratio, provided that the principles were met.
Another example is the regulation of roll stability - an effective roll warning device could more than compensate for a vehicle which did not meet a prescribed limit on roll threshold. Therefore any regulation which limits roll threshold should be linked to a principle about the prevention of rollover.
The people who prepare the regulations will probably be horrified at the thought of the inclusion many more words but the benefits to regulators and vehicle operators cannot be overlooked.
Dynamic wheel loads
David Cebon, from Cambridge University, gave an overview of vehicle/pavement interactions (the paper is not in the CD ROM). One outcome from recent findings seems to be that caution should be exercised when trying to apply the "4th power law" to "inflexible pavements".
On the matter of the "4th power law" it was interesting to see reference to the effects of "the merging of the tails of two bell curves" (to use Chris Winkler's description from a different context) in the paper "Pavement Variability and Reliability" by Bill Kennis and Weijun Wang (US Dept of Transport). Figure 4 of their paper shows the effect of merging bell curves. Several years ago, at a conference in Melbourne, I pointed out to Bill that the cumulative normal distribution curve and a fourth power curve can be very similar over a narrow range and that maybe there was a statistical explanation for the tests, conducted in the 1950's, on which the 4th power law is based. Note, however, that in the paper the merging bell curves are used to explain a different phenomena. As far as I can tell, there is still no physical explanation for the "4th power law".
Don Streit from Pennsylvannia State University presented a paper "Vehicle based weigh-in-motion system". This has potential to be a very low cost alternative to the use of expensive and cumbersome instrumented wheel hubs to measure dynamic wheels loads. The principle is that a sensor is located just inside the wheel rim at the six oclock position and the capacitance between the rim and the sensor is measured as the wheel rotates. Normally wheel run-out and other cyclic effects could be expected to swamp any effects due to deflection of the wheel and rim under dynamic loads. By sensing the angle of rotation of the wheel (on the prototype metal "lumps" were glued on the inside of the rim to produce spikes in the capacitance) and applying Fourier analysis techniques to eliminate spurious data, Don's team was able to obtain good correlation with a strain gauge system mounted on the axle.
The Australian Heavy Vehicle Standards prescribe signs for
B-doubles and Road Trains. I regularly hear discussion about the
effectiveness of these and other signs. Perhaps the sign should
"TO OVERTAKE OR NOT TO OVERTAKE: IS IT REALLY WORTH THE RISK?"
The point is that car drivers in Australia really need to be shaken out of the fixation "there a truck up ahead - I must overtake it as soon as possible". Twenty years ago or more a trip might have been noticeably delayed by being stuck behind a truck but that no longer applies to typical highway trucks. I once listened to a politician complaining that B-doubles were so large and fast that she could not overtake them at night in the rain. It begged the question "Why on Earth would you want to overtake in those circumstances?" but I refrained!
Les Bruzsa from Queensland Transport presented results of a comprehensive trial of B-triples in Queensland. The economic analysis was interesting because he compared the running costs (cents per tonne-kilometre) of a range of vehicles from conventional artics to road trains. Subject to Les's caution that the types of operation were not necessarily comparable he found that B-triples performed marginally better than B-doubles (about 29 cents compared with 33 cents, I recall) and that, surprisingly, road trains were slightly higher than B-doubles. The artic was about 42 cents per tonne kilometre.
Although the differences between the large combinations are marginal, they would add up to substantial savings over the year. However, if we are to consider the economics over an extended time for a large number of vehicles then it would be appropriate to also consider the cost of accidents since, under the same operating conditions, some types of vehicles are likely to be more prone to accidents (I don't think these costs were factored into the Queensland analysis). Another uncosted factor which would be considered by operators is the inconvenience of the restriction on area of operation of some configurations such as road trains.
Several authors mentioned the potential to use ITS/Telematics to automatically charge heavy vehicles on a distance travelled basis. One of many obstacles to successful implementation of such a scheme is the privacy issue. For those involved in road charging I can recommend a report prepared by Michael Schabas and published by the Centre for Policy Studies, London, titled "Charging for roads - a better way to ease congestion". The brilliant suggestion he makes is that there should be a high usage fee and vehicles registered under this fee would be ignored by the ITS/Telematic system. In other words, the operator pays a premium to have unlimited use of the road network and, as a result, remains anonymous to "big brother".
See Road Safety Web Links for
links to many of the organisations represented at the
email me if you have any
comments or wish to be added to that links page.
This web page prepared by Michael Paine, 4 April 1998. These notes are the author's views and do not represent the views or policy of any organisation.