Haulage

Haul truck queue time: practical causes and site fixes

Published 2026-11-12 · CycleStudy Pro

The cost of stationary haul trucks

In an open-pit mine, a haul truck standing in queue burns expensive fuel, runs down tire life without delivering tons, and inflates overall cycle time. When three or four 240-tonne trucks bunch up at a single excavator, shovel operators feel rushed, spotters face crowded loading bays, and the downstream crusher starves for feed while loaded trucks sit idling.

Measuring queue time ($t_{WaitT}$) is the foundation of haulage optimization. Ground observers define queue time as the exact span from when a haul truck arrives at the loading zone waiting line to when the driver begins the spotting reverse maneuver into the bay. In top-performing operations, target queue time is maintained below 15 seconds per cycle, while queue times exceeding 45 seconds trigger immediate dispatch intervention.

Mathematical definition of queuing losses

Total truck cycle time ($t_{TruckTotal}$) consists of fixed terminal components and variable transit legs:

Here, $t_{Spot}$ is spotting time, $t_{WaitT}$ is queue time, $t_{Load}$ is loading time, $t_{Exch}$ is exchange time, and $t_{DumpT}$ is dump pad time. The fixed share represents:

When the fixed haulage share climbs above 25% to 30%, queue time is almost invariably the primary offender. In severe over-trucking scenarios, queue time can exceed 25% of the total round trip, meaning a quarter of your haul fleet is effectively parked.

Root causes in pit operations

Three operational drivers generate persistent truck queues:

1. **Fleet Over-Trucking (Match Factor > 1.10):** Assigning more haul trucks than the shovel can service causes trucks to arrive faster than the shovel's bucket loading cycle ($t_{Load}$). 2. **Haul Road Bunching:** Speed variations on long uphill ramps and shift-start mass departures create truck platoons. When six trucks travel nose-to-tail, they arrive at the face simultaneously. 3. **Slow Exchange Times ($t_{Exch} > 35s$):** If the incoming truck takes 45 seconds to reverse or the shovel fails to clean the floor during the exchange, the entire queue backs up into the ramp entry.

Field fixes for pit supervisors

To eliminate destructive queuing without cutting overall shift tonnage:

- **Stagger Shift Starts:** Release haul trucks from the go-line in 90-second intervals based on bench haul distance rather than dispatching the entire fleet at once. - **Implement Double-Sided Loading:** Where bench width and safety berms permit, spot trucks on both sides of the shovel ($60^\circ - 75^\circ$ swing angles). This reduces exchange time to 18-25 seconds and cuts truck queue dwell time in half. - **Dynamic Re-Routing:** Monitor live queue counts. When a loading bay exceeds two waiting trucks, divert subsequent arrivals to an alternative shovel or waste dump run.