Plying a route on a mix of highways with different gross vehicle weight (GVW) restrictions, such as primary and secondary highways or private and public forest roads, forces trucks to load for the lowest-rated road. Sometimes there is no safe limit – typically in the springtime – and roads can be closed completely for several weeks. The former scenario drives down revenue; the latter shuts it off completely.

In several provinces however, the implementation of tire pressure control systems (TPCS) and related record-keeping equipment has several Departments of Transportation authorizing higher GVW for TPCS-equipped rigs on weight-sensitive roads; TPCS lets drivers lower and raise their tire pressure to pre-set levels with a touch of a button in the cab.

The secret to increasing the road load limits is lower tire pressure, because underinflated tires distribute weight over more road surface. The Forest Engineering Research Institute of Canada (FERIC) has studied the relationship between load weight, tire pressure and road damage and shown that lowering tire pressure from 100 psi to 50 psi nearly doubles the contact area with the road and distributes loads far more uniformly over the road surface. As well, the tire sidewalls bulge more, and act as a second set of shock absorbers to reduce the hammering of the road, according to Allan Bradley, a senior researcher in the Road Group in FERIC’s Western Division.

The reality then, is that truck A, hauling 65,000-kilograms on 55-psi tires, may stress a road no more than truck B hauling 55,000 kg on 95-psi tires. So why not let Truck A travel roads rated for truck B?

And indeed, the Departments of Transportation in Saskatchewan and British Columbia are doing this; New Brunswick is running trials; there is ongoing research with forestry companies in Newfoundland and Quebec; and similar activity in Nova Scotia.

FERIC supplied the evidence. What remained was to bring together technologies so drivers could change tire pressure on the fly and regulators could be confident that participating trucks were compliant.

Drivers on a primary road might select a tire pressure of 95 psi. For a secondary road with a lower maximum permitted GVW, they can select, say, 55 psi. The only compromise is having to slow down to prevent tire overheating.

The TPCS is connected to global position system (GPS) equipment, computers and transmitters that record and transmit position and tire pressure information either to the trucking companies, which must present the data to on demand to DoTs, or directly to DoT Web sites. Weight data is collected at weigh scales and manually entered in to the databases.

In Saskatoon, Federated Co-operatives Ltd. has been using TPCS since 1996. Federated runs B-trains equipped with TIREBOSS, a TPCS system manufactured by Tire Pressure Control International Ltd. in Edmonton. A system typically costs around $25,000.

“We deal with a big-time rural market, so we drive secondary roads often. Each truck would find themselves on a secondary road every day,” says Federated petroleum distribution services manager Craig Kezama.

On primary roads the trucks run at 90 psi and up to 90 km/h – 65 psi and up to 80 km/h on the secondary roads. TPCS is worth the up front cost, says Kezama. “The payback has been very good.”

For Saskatoon’s Winn Bay Sand LP, installing TPCS was the only way to make its new sand mining industry viable. Five company eight-axle B-trains and seven B-trains owned by lease operators have been using TIREBOSS since 2003 on a 922-km round-trip dedicated run between Saskatoon and Hanson Lake, Man. The route is roughly equally split between primary and secondary roads.

The normal secondary highway GVW is 54,500 kg year round, and 62,500 kg on the primary highway. But with TPCS Winn can haul 65,500 kg year round on both road types; an agreement with Saskatchewan Highways and Transportation lets both Winn and Federated exceed the usual maximum GVW for the primary highways. On the secondary roads Winn trucks begin at 60 psi for the tractor wheels and 55 psi for the trailer wheels, and drive a maximum 80 km/h. For the primary road drivers select 90 psi on their TPCS; once inflated, in roughly eight minutes, they speed up to 90 km/h.

Winn Bay Sand collects GPS, speed and tire pressure data and periodically downloads it to its database. Saskatoon-based International Road Dynamics (IRD), which designs and installs Intelligent Transportation Systems, picks up the data and makes it available upon request to Saskatchewan Highways and Transportation.

For Federated, IRD handles transmission of location, speed and tire pressure data. Every five minutes the data is sent via satellite to Federated’s distribution office in Regina.

The program has been successful, according to Saskatchewan Highways and Transportation director of trucking programs Bill Cook. He believes that the program will grow, but notes that it will be for industries that regularly use a combination of secondary and primary roads.

In British Columbia, forestry company Tembec has been using TPCS since the spring of 2003 to get fully-loaded logging trucks across “pinch points” – sections of weight-restricted gravel roads between non-restricted forestry roads and normal-GVW primary roads.

Under normal seasonal load restrictions – when the roads remain open at all, that is – a truck can typically run to 70% of normal load. Those using TPCS can haul 100% loads [55,300 kilograms GVW] on the roads at that time, according to Jack Bennetto, the district manger, transportation, with the British Columbia Ministry of Transport.

“We asked the industry to submit their proposal in late October to run CTI on a particular road. To date all the roads that have been applied for have been approved; we like to encourage this. Because this is a new policy, we are monitoring the roads, and so far we have had positive results. We didn’t see road damage, so we are comfortable applying this as policy,” Bennetto says.

There are currently 20 TPCS-equipped contract trucks working for Tembec, says Duke Armleder, technical manager for forest resource management for Tembec’s British Columbia Division. “In the first year we got buy-in from 11 trucks. That rose to 20 trucks in the second year. The trucks work two months more with TPCS. In 2004 hauled 70,000 cubic metres of wood during the restricted period.”

In Tembec’s Northern Ontario Eastern Division, Cochran Unit, operations superintendent Ken Johnston has been working with TPCS since 2004, with seven trucks and two floats the first year, and 12 trucks and two floats the next. Johnston’s problem is not GVW-restricted roads, but rather, expensive company roads built on swamp and clay.

“Using Central Tire Inflation [an older term for what is now more precisely referred to as TPCS] has to do with accessing the forest, period,” explains Johnston. “In our area, the clay belt region, which has always been a winter logging story, we do not have a lot of summer haul road.

“Before CTI, the [road] layer was 1.5 – 2.0 feet thick gravel that had to be hauled in, resulting in expensive roads. The idea now is to reduce our roads costs by using clay over rootmat, material which is located near the sides of the road.

“We are currently building a rootmat (stumps, moss and roots) with about one foot of clay. Sand and or gravel are applied sparingly over this clay road. The CTI technology and our clay roads over rootmat are now allowing us to haul from these areas that were too expensive to access with our older, more expensive roads.

“It gives us more of a window in the nonfrost conditions to move wood. It has the potential to reduce the maintenance on the roads we have. We are anticipating a 50% reduction in road maintenance.”

On pavement, the TPCS trucks run at 80-90 km/h at 100 psi. On Tembec’s main gravel road they travel at 60 km/h at 65 psi. On tertiary roads, which is a simple bulldozed road designed to last one year, the logging trucks plod along a
t 20-30 km/h and 40-50 psi.

There are implications for Tembec’s contractors associated with creating what some call “CTI roads”, says Johnston. “We don’t want non-CTI trucks on CTI roads. They will damage these roads beyond repair. Part of our commitment to our CTI guys is that they have first priority to haul during the summer months, and they are the only ones to haul on our cheaper built clay over rootmat roads. CTI enables them to have more opportunity to haul during the non-frost conditions.

FERIC is working with Quebec forestry companies to explore the benefits of TPCS. New Brunswick Transport says that it began TPCS tests in the spring of 2004, but it does not yet have conclusive results to report.

As the tires spread, so does the trend to using TPCS, allowing beleaguered trucking companies to boost their bottom lines. With TPCS, says Armleder, “You are running the perfect and proper inflation for the road, load and speed.”