Low volume roads, which include the 600-Series highways in Northern Ontario, are not designed to the same structural strength as high volume roads. These roads are at their weakest during spring-thaw, when the sub-grade is saturated. Most transportation agencies in northern climates reduce the allowable weight of trucks on designated roads during spring-thaw to avoid excessive damage to the road. Spring Load Restrictions (SLR) reduce the legal axle loads carried during this period by half, typically from mid-March to mid-May (9 – 10 weeks). (For more information, please see summer 2006 Road Talk article “Flexible Spring Loads"; pg 5). SLR impacts the heavy haul, truck-based industries, such as the forest industry.
Recently, the forest industry has adopted a new technology on their trucks for use when hauling on forest roads, which they have found substantially, reduces the impact to road surfaces. This Central Tire Inflation (CTI) technology is well established, having been used for decades by the military. From the truck cabin, while stationary or moving, the truck driver can reduce the tire pressure, and increase the tire footprint. The net effect is a reduction of both static and dynamic loads on the road surface, and less impact to the road structure. When travelling on non-SLR posted road surfaces the tires can be centrally re-inflated back to a normal pressure.
The forest industry, represented by the Forest Engineering Research Institute of Canada (FERIC), approached the Ministry of Transportation Ontario (MTO) in 2005 with a request to partner in a series of demonstrations and trials, with the goal of MTO adopting CTI during the last 3-4 weeks of an SLR period. FERIC proposed that a British Columbia model be tried.
British Columbia carried out trials in 2000, 2003, and 2004 before allowing CTI-equipped trucks to haul full loads during the latter part of their SLR period. As a condition of participation in BC's Tire Pressure Control System (TPCS) SLR program, the participant is required to retain the services of a qualified company to carry out Benkelman Beam deflection testing, and achieve a deflection reading below 1.5mm. In addition, the trucks must be equipped with an on-board computer (OBC), TPCS, and GPS. The OBC collects trip information on tire pressure, truck speed, and GPS-based routing. This trip data is offloaded at the mill scale in an encrypted format and combined with scale-measured axle weights after each trip. Finally the data is transferred to a data management company who receives the data, compares it to BC Ministry of Transportation specified tolerances, and posts a compliance report immediately to a secure web site for inspection by all stakeholders.
The ministry was willing to evaluate the British Columbia model, but instead of using Benkelman Beam technology, MTO proposed that the road deflection be measured using a new, highly efficient instrument, the Portable Falling Weight Deflectometer (PFWD), to determine when the pavement may safely carry TPCS-hauls.
In Spring 2006, a TPCS field trial conducted by FERIC, MTO and Tembec Industries on Highway 630 (Phase I) was considered by all participants to be a success in terms of demonstrating the technology, capture of TPCS data, data transmission and monitoring the condition of the pavement (which was unaffected by the trial). However, this trial represented findings at only one site, in one season, with an average of eight loads per day, hauled out of a stockpile.
In order to make a decision on CTI policy, MTO proposed a trial to demonstrate that the technology can be used under commercial, large-scale hauling conditions and that it can be regulated by simple, inexpensive means based on solid scientific principles, specifically, a model utilizing a combination of PFWD measurements, freeze-thaw depths, and Road Weather Information System (RWIS) data.
The Centre for Pavement and Transportation Technology (CPATT) at the University of Waterloo was brought on-board to carry out this next phase of research, since CPATT was involved with a parallel MTO project to provide scientific tools for establishing the SLR period limits.
Two sites were proposed for the next phase of the project, based on wood allocation, to commercially demonstrate the technology and prototype an administrative operating environment. The site chosen in Northwestern Region is on Hwy 601 (from 1.6 km north of Hwy. 17 west junction for 9.3 km north). The other site in Northeastern Region is on Hwy 651 (from Hwy. 101 junction for 28 km north).
To-date both test sites have been surveyed and baseline deflection readings taken. In late October, instrumentation to measure frost depth will be installed. The main activity, hauling 15 loads per day of wood chips or logs, will commence mid-April 2008.
The ministry has made a considerable commitment to this project, in support of the development of innovative technologies that encourage economic growth and prosperity of the province, while ensuring that the condition of our highways is not at risk.