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46 to exploit the new form of regulation, but not all those that higher than expected, based on the amount of freight carried arose were foreseen. Nor was the widespread use of liftable and the vehicle configuration. The actual outcome will be far axles foreseen, with the consequent road damage and risk to worse than the desired outcome. bridges that amounted to Can$300 million in additional maintenance costs per year by about 2000. They could not 3.4.4 The Need to Monitor Outcomes foresee the poor dynamic performance of some of the config- urations, as heavy vehicle dynamics was still in its infancy at Highway departments put much thought into a new or that time. It took 30 years for Ontario to start a process to re- amended truck size and weight regulation. Once a new regu- vise what it did in 1970, another 10 years for this process to lation is in place, vehicle designers, sales personnel, carrier address all configurations, and it may be another 20 years be- fleet managers, and drivers put considerable effort into look- fore all the old configurations are finally retired. ing for ways to use the regulation that will give them a com- The M.o.U. provided comprehensive definitions of terms, mercial advantage over their competitors. These people are and detailed and complete specifications for vehicles, to guard very innovative and spend a lot of time thinking, so it may not against the unexpected outcomes that occurred in Ontario. be surprising that the outcomes may not always be those in- These vehicles have, generally, achieved the intended outcomes. tended. It is critical therefore to monitor the effects of the reg- Some jurisdictions have a tendency to write vehicle specifi- ulations to ensure that negative, unintended consequences cations as "A vehicle with (so many) axles shall . . ." followed can be rectified early. by some general dimensional limits and allowable weights. The intention of the B-train specification in the M.o.U. was Such a vague form does not define a vehicle configuration, and that vehicles meeting the specification should look and per- may result in a straight truck, truck-pony trailer, truck-full form like B-trains. One of the earliest vehicles proposed was es- trailer, tractor-semitrailer, A- or B-train double trailer combi- sentially a jeep dolly towing a 14.65-m (48-ft) semitrailer, which nation, or some other configuration depending on the num- met the then-current B-train specification, but took much ber of axles and length allowed. Even if the configuration is more space to turn than a tractor-semitrailer. It was shortly fol- specified, as more axles are allowed, the number of ways the lowed by a tractor-semitrailer with a low-mounted stinger axles can be arranged within each vehicle unit, and over the fifth wheel towing a pony trailer, which also met the specifica- vehicle as a whole, increases exponentially. There is a dramatic tion, but had much less desirable dynamic performance than a range of difference in the dynamic performance of the possi- proper B-train. Once these configurations were observed, the ble configurations, which may have some bearing on the crash Task Force on Vehicle Weights and Dimensions Policy moved rate and the types of crash. Certain dimensions are important quickly to change the B-train specification to preclude them. In to the dynamic performance of some configurations, and the first case, no vehicles were built. In the second case, a small these should have strict limits, but this vague form of specifi- number were built, but only in one province. cation generally does not address these. If 6 or more axles are Monitoring the outcomes of the regulations determined available, then some of these axles will certainly be liftable, as the presence of the deviant configurations. The response pre- is evident in states that allow use of the Federal Bridge For- vented an unintended outcome as it prevented these vehicles mula without other constraints, such as in Washington and becoming numerous, and avoided a need to grandfather Ohio, where vehicles with one or more liftable axles are com- those that had been built for the rest of their useful lives. mon. Michigan allows up to 11 axles, with allowable gross Monitoring the evolution of the fleet resulting from weight determined simply by the sum of allowable axle group changes in regulation provides valuable insight into the effec- loads, and has vehicles with 5 or more liftable axles. tiveness of a given regulatory initiative. A recent study (88) on When a vehicle has a liftable axle with an independent sus- the impact of Canadian size and weight regulation change in pension, the driver sets the load on the liftable axle. Experi- the Prairie Provinces describes how the new policies have in- ence in Canada suggests that a liftable axle is usually down fluenced the fleet mix, resulting in more productive vehicles. when it needs to be down, but it is often loaded less than it It also found that when the new policies were implemented, needs to be, based on the overall load on the vehicle, so other it took 8 to 12 years for the carriers to fully adjust their fleet. axles are overloaded. It is possible that the driver sets the liftable axle to that load that makes the vehicle easiest to drive, 3.4.5 The Need for Dimensional rather than the load necessary based on the total load on the Compatibility vehicle. Many load controls are also not very reliable, so the set load may vary during a trip. The actual axle loads arising A vehicle may travel between jurisdictions if it is within the from the way the liftable axle is set determine the amount dimensional limits allowed in each jurisdiction. It cannot travel of pavement resource consumed on a trip, and the risk to where it is not within the dimensional limits of a jurisdiction. A bridges. When liftable axles are used, this will be considerably fundamental aspect of harmonization of truck size and weight