Canadian Forest Industries Magazine

Slippery Slopes?

How steep is too steep? That's a question that has plagued the forestry industry in BC since a runaway truck careened off a steep logging road grade in 2003, killing the driver. Since then, WorkSafe BC and logging companies have been struggling to determine the maximum grades that can be safely traversed by logging trucks. FERIC got involved, and has recently completed a report on 'fat trucks' (off-highway logging trucks with axle widths of 3.34 metres hauling payloads of up to 120 tonnes) and logging road grade limits.

Logging road grades have been getting steeper, and that's not necessarily a bad thing for forestry companies. They can reduce their road-building requirements (and environmental footprint) by building roads on steep ridges rather than unstable slopes in mountainous terrain. New trucks have also allowed forest companies to push the envelope, as advances in engine brakes have increased the slowing power of heavy trucks.

But these trends have created new dangers for off-highway log haulers, many of whom have never encountered such steep grades despite their usually extensive off-road driving experience.

"There have been a lot of situations where WorkSafe BC has had to shut down hauling because of concerns about steep grades," explained Seamus Parker, senior researcher with FERIC. "Our members came to us to analyze the situation, and to see what conditions they can safely haul at."

BC forest road grades are separated into two categories: Over and under 18%. It's generally assumed that a well maintained logging truck can safely navigate grades of 18% or less without any difficulties. Grades over 18%, however, are a more complicated matter - and there is no shortage of them in BC. In fact, the grade that claimed the life of the aforementioned driver in 2003 was a 26% white-knuckler.

Calculated Risks

BC requires that logging companies perform a risk assessment on grades steeper than 18%, as well as develop safe descent procedures. FERIC wrote its recent report to assist forestry companies in this process. The study involved equipping a fat truck with onboard instrumentation that measured all kinds of data to determine the retardation and stopping limitations of heavy trucks on steep downhill grades.

Parker found that in many cases, the driver can have a significant influence on a truck's ability to safely descend steep grades.

"They get a little complacent sometimes and don't take the proper precautions, like ensuring the brakes are adjusted properly, which was a factor in the fatality," Parker said. "There are specific speeds they can go down - they want to go down as slowly as possible," he added, noting gear selection is the most important consideration.

Fat trucks don't use automatic slack adjusters, due to the harsh operating environment they run in. So drivers are urged to regularly check to ensure their brakes are in adjustment. Since most of the braking is done by the engine retarder, Parker said drivers often neglect to maintain the service brakes. As a result, they're not always there when needed. "There's too much reliance on the engine brake," he pointed out.

As well as maintenance, Parker said traction plays an important role in determining whether or not a truck can safely descend a steep grade.

"If you don't have the right traction conditions, you can't go down and expect to stop," he said.

The FERIC study found that the driveline accounts for about 35-55% of retardation on steep declines, while the service brakes only provide 10-20% of a truck's stopping power. The rest can be attributed to rolling resistance. As a result of this finding, FERIC was able to develop a detailed set of guidelines on steep grade descent limitations. The data should prove invaluable to forest company road planners. (The full report can be downloaded from FERIC's website at www.feric.ca).

Some of the main suggestions emerging from the study included:

• Forest operations planners should review current road networks in light of the guidelines contained in the report.
• Load weights should be limited to each specific harvest block, and the use of on-board scales should be encouraged.
• Load height should be limited to 6.4 metres to improve stability.
• Trucks should be properly maintained at all times.
• The best available road-building materials should be used to maximize traction.
• Hauling should be halted when traction is compromised by snow or ice.
• Steering axle brakes should be used and maintained to improve retardation levels.
• Brake temperatures and air chamber stroke should be monitored closely.

Next up, FERIC plans to conduct a similar study for on-highway trucks.

"Highway trucks have more axles, better braking capacity and they're geared to go a little faster, but they also have more brakes which allows them a greater ability to go down steeper grades," said Parker. That study is already underway, and its findings will be of interest to log haulers right across the country.

James Menzies is executive editor with Trucks West, and writes this column exclusively for CFI Magazine