In mining and heavy industry, haul road geometry is the primary driver of operational costs and site safety. Poorly designed roads don’t just slow trucks down; they accelerate mechanical failure and increase the risk of catastrophic accidents [1]. Let’s explore how the three core geometric factors: width, grade, and curvature impact both safety and productivity.
Road width
Road width is primarily a safety constraint that, if insufficient, forces productivity-killing speed reductions. Standard safety guidelines usually require a road width of 3 to 3.5 times the width of the widest truck for two-way traffic [2]. This provides a “buffer zone” to prevent side-swipe collisions. Proper width allows for the construction of safety berms (usually at least half the wheel height of the largest truck) without encroaching on the travel lane. Wider roads reduce “blind spots,” especially in areas where light-duty vehicles share the road with massive haul trucks [3].
Adequate width allows operators to maintain rated speeds during passing maneuvers [3]. If a road is too narrow, trucks must slow down or stop at “pull-outs,” increasing cycle times and fuel consumption. Narrow roads limit a mine’s ability to upgrade to larger, more efficient truck classes in the future.
Road grade (Gradient)
Grade is the “engine killer.” It determines the maximum potential speed of the truck and the thermal load on the braking system. Steep downhill grades (typically above 10%) can lead to retarder or brake overheating. If a grade is inconsistent (varying between 8% and 13%), drivers may struggle to maintain a safe “constant speed” descent [4]. Steep gradients increase the severity of mechanical failures.
The “ideal” grade for most haul fleets is between 8% and 10%. Constant grades are critical; if the grade fluctuates, the truck’s automatic transmission will constantly “hunt” for gears, leading to power loss, increased fuel burn, and drivetrain wear [3]. A 1% increase in effective grade can significantly reduce the uphill speed of a loaded truck, directly lowering the “tons per hour” the fleet can move.
Curvature and super-elevation
Curvature manages the lateral forces acting on the truck’s tires and frame [3]. Tight curves without proper super-elevation (banking) create centrifugal forces that can cause a truck to slide or tip. Curves limit how far ahead a driver can see. Proper design ensures the “stopping sight distance” is always greater than the distance required to bring a 400-ton machine to a full stop.
In tight curves or switchbacks, the inner and outer tires travel different distances. This causes “scuffing,” which tears the tread and generates heat, leading to premature tire failure (one of the highest costs in mining) [2]. Poorly transitioned curves (going from flat to banked too quickly) cause “frame twist,” leading to metal fatigue and expensive structural repairs to the truck chassis.
Reference
[1] A. Shakenov, “OPTIMAL SLOPES OF MINE HAUL ROADS,” Jul. 2022.
[2] “ZKG international.” Accessed: Jan. 15, 2026. [Online]. Available: https://www.zkg.de/en/artikel/zkg_Road_Maintenance_Safety-2273698.html
[3] pcm_admin, “Optimised haul roads key to efficiency and longevity,” Quarry. Accessed: Jan. 15, 2026. [Online]. Available: https://www.quarrymagazine.com/optimised-haul-roads-key-to-efficiency-and-longevity/
