Use IRI to Reduce Haul Road Downtime, and Increase Safety

Why haul road roughness matters

Mine haul roads, gravel roads, and resource access roads are essential operating assets. They carry production vehicles, fuel, supplies, personnel, and expensive equipment across the site.

When these roads become excessively rough, the effects go beyond driver comfort. Rough sections can reduce travel speeds, increase haul-cycle times, damage vehicles, create risks for sensitive loads, and eventually contribute to unplanned road closures.

Haul road roughness monitoring gives operators an objective way to identify deterioration early and complete routine maintenance before conditions become a larger operational problem.

Using IRI to monitor road condition

International Roughness Index, or IRI, is a standardized measure of longitudinal road roughness. Higher IRI values indicate a rougher road surface.

For mine and gravel roads, the value of IRI comes from collecting it repeatedly across the same road sections. This allows operators to track changes over time and determine whether each section remains within an acceptable operating range.

An operation can establish internal condition categories such as:

• Normal operating condition
• Monitor or watch condition
• Maintenance required
• Immediate inspection required

When a section moves outside its acceptable range, the result can trigger an inspection, grading, spot repair, drainage correction, compaction, or surface material replacement.

The goal is not simply to produce an IRI number. The goal is to use the number as an operational trigger before road deterioration begins affecting production, equipment, or safety.

Reducing the risk of unplanned downtime

Gravel and haul roads can deteriorate quickly due to heavy loading, rainfall, drainage problems, corrugation, rutting, potholes, or surface material loss.

If these changes are not identified early, a manageable maintenance issue can develop into a failure that affects production, access, deliveries, or emergency response.

The potential production impact can become significant very quickly.

Consider a simplified operation with:

• 10 haul trucks
• A payload of 200 tonnes per truck
• A 45-minute complete haul cycle

Under normal operating conditions, this fleet could move approximately 2,670 tonnes per hour. A four-hour closure of a critical haul route could therefore delay the movement of more than 10,000 tonnes of material.

The actual financial effect depends on the value of the material, processing capacity, stockpiles, alternate routes, and whether production must stop completely. However, even a partial interruption can cost substantially more than routine grading, drainage correction, or spot repairs.

Regular IRI monitoring helps teams detect increasing roughness before the road becomes difficult or unsafe to operate. This supports planned maintenance instead of emergency intervention.

The cumulative cost of slower travel

A road does not need to become completely impassable before it begins costing the operation money.

A relatively small reduction in average vehicle speed can create a large cumulative impact when trucks travel the same route repeatedly.

For example, travelling across a five-kilometre road section takes:

• 10 minutes at an average speed of 30 km/h
• 12 minutes at an average speed of 25 km/h

That is only two additional minutes per pass. However, at 100 truck passes per day, the rough section consumes approximately 3.3 additional truck-hours every day.

Over one year of continuous operation, this represents approximately 1,200 additional truck-hours.

The operation can multiply that figure by its internal cost per truck-hour to estimate the effect on fuel, operators, equipment availability, maintenance, and production.

This calculation does not include queuing, downstream delays, or the cost of adding more trucks to maintain the same production target.

Regular roughness monitoring helps identify these slow sections before the resulting productivity loss becomes accepted as part of normal operations.

Keeping roads within operational tolerances

The objective is not necessarily to keep every mine road as smooth as a paved highway. Different roads can operate effectively at different roughness levels.

A primary production route may require a tighter tolerance than a low-volume access road. Routes carrying sensitive, hazardous, or high-value loads may also require stricter monitoring.

Appropriate roughness tolerances should consider:

• Vehicle type and loading
• Normal operating speed
• Traffic volume
• Road surface material
• Production importance
• Cargo sensitivity
• Seasonal conditions
• Site safety requirements

There is no universal IRI threshold that is appropriate for every haul road.

Each operation should develop internal thresholds based on its vehicles, road conditions, maintenance standards, operating requirements, and historical results.

Once these tolerances are established, IRI can be used to identify roads that remain acceptable, sections that should be watched, and locations requiring maintenance or immediate inspection.

Understanding the effect of rolling resistance

IRI and rolling resistance are different measurements.

IRI measures longitudinal road roughness, while rolling resistance describes the force required to move a vehicle over the road surface.

However, many conditions that increase roughness, including corrugation, rutting, loose material, potholes, and surface deformation, can also increase resistance, vibration, speed variation, and energy consumption.

Each additional one percentage point of rolling resistance creates a resisting force equal to approximately one percent of the vehicle’s gross weight.

For an illustrative loaded truck weighing 400 tonnes:

• A one percentage point increase in rolling resistance adds approximately 39 kilonewtons of resistance
• This is equivalent to approximately four tonnes of additional continuous pulling force
• At 25 km/h, overcoming that additional resistance requires approximately 273 kilowatts of wheel power

If road condition adds two percentage points of rolling resistance, the additional resistance increases to approximately 78 kilonewtons, or eight tonnes of continuous pulling force. At 25 km/h, this represents approximately 545 kilowatts of additional wheel power.

These calculations do not mean that a specific increase in IRI automatically produces the same increase in rolling resistance.

They demonstrate why changes in road surface condition can create a major energy and productivity penalty for extremely heavy vehicles.

IRI can provide an early warning that a road section is becoming rougher and should be inspected for conditions that may also be increasing rolling resistance.

Potential fuel savings across a fleet

Fuel consumption depends on road grade, vehicle size, payload, speed, surface condition, driving practices, and the proportion of each cycle spent on the affected road.

A mine can still use a simple sensitivity calculation to determine whether improved road maintenance could produce a worthwhile return.

Consider an illustrative fleet with:

• 10 haul trucks
• Average fuel consumption of 100 litres per operating hour
• 4,000 operating hours per truck each year

This fleet would consume approximately four million litres of fuel annually.

If improved road condition, more consistent speeds, and lower resistance reduced total fleet fuel consumption by only 2-5%, the annual fuel reduction would be approximately 80,000-200,000 litres.

At a delivered diesel cost of $1.00 per litre, that represents approximately $80,000-$200,000 per year.

At $1.20 per litre, the range increases to approximately $96,000-$240,000 per year.

The 2-5% range is an illustrative planning scenario rather than a guaranteed result. The actual effect should be measured using the mine’s own fuel, telematics, and road-condition data.

Protecting expensive vehicles and equipment

Mining and resource vehicles are expensive to purchase, operate, maintain, and replace.

Rough roads expose these vehicles to repeated vibration, impact, and dynamic loading. This can increase stress on:

• Tires and wheels
• Suspension and steering systems
• Frames and structural connections
• Hydraulic components
• Mounted instruments and electronics
• Vehicle bodies and cabs

Road roughness is not the only factor affecting equipment wear. Vehicle speed, loading, tire pressure, suspension design, driving practices, and environmental conditions also contribute.

However, the financial case for better road maintenance does not require a dramatic reduction in equipment costs to be worthwhile.

For example, assume an operation spends $2 million annually on maintenance categories that may be affected by road condition, including tires, wheels, suspension, steering, frame repairs, mounted components, and vibration-related failures.

• A 5% reduction in those costs would save approximately $100,000 per year
• A 10% reduction would save approximately $200,000 per year

These percentages are illustrative scenarios rather than universal industry benchmarks.

The most useful calculation will use the operation’s actual maintenance records.

IRI trends can be compared with:

• Tire replacement frequency
• Suspension and steering repairs
• Cracked frames or structural components
• Wheel and bearing repairs
• Hydraulic and electrical failures
• Unplanned vehicle downtime
• Maintenance labour hours

If equipment repair frequency increases as specific road sections become rougher, the operation has a measurable basis for comparing the cost of road maintenance against the cost of continued equipment damage.

Supporting hazardous and sensitive transport

Some mining and industrial operations transport materials or equipment that are sensitive to vibration, shock, or excessive movement.

These may include fuel, chemicals, hazardous materials, explosives handled under approved procedures, sensitive instruments, or high-value components.

Maintaining these routes within a defined roughness tolerance can support a broader transportation risk-management process.

An operation may choose to survey critical routes regularly or before specific movements.

If a section exceeds the established tolerance, the team can inspect the road, complete maintenance, reduce travel speed, modify the transport plan, or apply other controls.

This provides a measurable way to determine whether the transport route remains within the operating condition established by the organization.

IRI monitoring does not replace applicable transportation regulations, vehicle inspections, load securement requirements, or site safety procedures. It provides an additional objective measure of road condition.

Prioritizing maintenance resources

Maintenance teams often have limited time, equipment, material, and staff.

Without objective condition information, road maintenance can become reactive. Crews may be sent to the location with the most recent complaint or the most visible defect rather than the road presenting the greatest operational risk.

A mapped IRI survey helps identify which road sections are the roughest and which are deteriorating most quickly.

Maintenance can then be prioritized based on:

• Sections exceeding the intervention threshold
• Primary production routes
• Roads carrying sensitive loads
• Locations associated with reduced travel speed
• Sections with recurring drainage problems
• Areas showing rapid deterioration
• Routes associated with high equipment costs

This helps direct limited maintenance resources toward the road sections most likely to affect production, equipment reliability, or safety.

Verifying that maintenance was effective

IRI can also be collected before and after maintenance to verify whether the work produced a measurable improvement.

A basic verification process includes:

1. Collect baseline IRI before maintenance.
2. Identify sections outside the acceptable range.
3. Complete grading or corrective work.
4. Survey the same sections again.
5. Compare the before-and-after results.

This provides objective evidence that maintenance was effective and helps identify sections that may require more than repeated grading.

It can also support contractor management.

If an external contractor performs the work, the operation can define an expected roughness tolerance and verify whether the road was returned to the agreed operating range.

Repeated before-and-after measurements can also help determine which maintenance methods produce the longest-lasting improvement.

Identifying rapid deterioration

A single IRI survey shows current road roughness. Repeated surveys show how quickly the condition is changing.

Two road sections may have the same current IRI, but one may have remained stable for months while the other deteriorated rapidly after rainfall or heavy loading.

Rapid deterioration may indicate:

• Inadequate drainage
• Weak subgrade
• Insufficient surface material
• Poor compaction
• Material contamination
• Water accumulation
• Concentrated wheel paths
• Inappropriate grading practices

IRI does not identify the exact cause by itself.

It helps identify where condition is changing so engineering and maintenance teams can focus their inspection and corrective work.

Building a practical monitoring program

A basic haul road roughness monitoring program can follow a simple process:

1. Divide the network into consistent road sections.
2. Collect a baseline while roads are operating acceptably.
3. Establish preliminary warning and maintenance thresholds.
4. Survey critical routes at regular intervals.
5. Inspect sections that exceed the threshold.
6. Collect IRI again after maintenance.
7. Review trends to identify recurring problems.

Survey frequency should reflect the importance and risk of each road.

Critical production routes may be surveyed weekly or monthly, while lower-volume roads may require less frequent collection.

Additional surveys may be completed:

• After heavy rainfall
• After abnormal loading
• Before sensitive transport movements
• Before and after grading
• After drainage work
• When operators report a sudden change in road condition

Building a site-specific business case

The most reliable savings estimate comes from combining IRI results with the operation’s existing fleet, maintenance, and production records.

Useful figures include:

• Fuel consumption per truck-hour
• Cost per operating truck-hour
• Average speed by road section
• Cycle time by route
• Tonnes moved per hour
• Tire and suspension costs
• Unplanned repair hours
• Road maintenance costs
• Production losses during route closures

The operation can establish a baseline and compare the period before maintenance with the period after maintenance.

Measure	Before maintenance	After maintenance	Change
Average IRI	Site result	Site result	Percentage improvement
Average truck speed	Site result	Site result	Time saved per cycle
Fuel per cycle	Site result	Site result	Litres saved
Maintenance cost	Site result	Site result	Cost avoided
Tonnes moved per hour	Site result	Site result	Production increase

This allows each mine to develop its own relationship between road roughness, maintenance activity, equipment cost, and production performance.

Once that relationship has been established, IRI thresholds can be based on actual operating costs and risks rather than an arbitrary road condition rating.

Using TotalPave for haul road monitoring

TotalPave IRI allows road roughness data to be collected using a smartphone mounted in a vehicle.

The system can be used to:

• Survey mine, haul, gravel, and resource roads
• Map results to consistent road sections
• Identify rough sections
• Compare repeated surveys
• Measure before-and-after maintenance results
• Review changes in road condition over time
• Export detailed road condition data

Because the system does not require a specialized profiling vehicle, data can be collected regularly using vehicles already available at or near the site.

This makes IRI practical as a routine maintenance-control tool rather than an occasional engineering study.

Turning roughness data into better decisions

The value of IRI is not the measurement by itself. The value comes from using the data to make earlier and better maintenance decisions.

Regular haul road roughness monitoring can help mines:

• Reduce the risk of unplanned road downtime
• Identify deterioration before it becomes a major failure
• Protect expensive vehicles and equipment
• Reduce fuel and operating costs
• Maintain production speeds and haul-cycle performance
• Support the movement of sensitive loads
• Prioritize maintenance resources
• Verify completed maintenance work
• Identify recurring road and drainage problems
• Develop site-specific maintenance thresholds

Regular monitoring turns haul road maintenance from a reactive activity into a measurable operating process.

To learn more about collecting your own road roughness data, review TotalPave IRI or contact TotalPave to discuss your road network.