Safety initiative for dairy tanker drivers

Data from the National Transport Insurance (NTI) National Truck Accident Research Centre (NTARC) shows that, on average, dairy tankers are 2.4 times more likely to be involved in a crash than other freight transport types.

That frightening statistic led NTI, with partial funding through the National Heavy Vehicle Regulator’s (NHVR) Heavy Vehicle Safety Initiative, to investigate just what was going wrong.

At trucksales we have some empathy with milk tanker drivers, having done a few farm-pickup stints in the past, while testing new trucks. The experiences of coping with variably shifting loads and dodgy access roads remain with us.

Milk transport is a vital part of a very big business. IBISWorld’s Milk and Cream Processing in Australia reported that we produce $4.3 billion and export around $621 million worth of milk annually. Dairy Australia data indicates that there are around 5700 dairy farms in Australia, with widely varying access, loading facilities and production amounts.

Milk production rates vary considerably due to seasonal factors, particularly in Australia’s southeast. When rainfall is generous in early spring, high-quality grass is abundant and cows produce much more milk for a few months. In typical years, production is highest between August and January, with peaks in October to November.

Essentially, road milk tankers visit dairy farms in sequence and then return to the milk processing plant. That means, within one driving shift, the trailer(s) become progressively heavier. This is known as ‘milk gain’ and directly relates to a combination’s stability and driveability.

Experienced milk tanker drivers know about this quirk, but during peak times, permanent dairy tanker drivers’ workloads increase and operators may need seasonal drivers to meet demand, increasing crash risks.

Drivers in some areas change vehicles frequently, sometimes daily. They may not know which vehicle or combination they will be driving until they turn up at the depot.

Complicating truck scheduling arrangements is the fact that cows’ daily milk production can vary by ten per cent and there are possible milk-weight variations between farms, making volume calculations difficult.

In many regions, milk pick-ups take place around the clock and most transport companies have both day- and night-shift drivers.

Obviously, milk tanker operators want to take advantage of the latest payload-efficient vehicle configurations, but road and farm access conditions can limit the usable types and sizes of trucks. Many minor roads will not allow 26-metre B-Double or PBS-vehicle access.

The milk cartage industry currently uses many vehicle combinations, operating on access and mass schemes that vary considerably across the fleet and its routes. Most common combinations are six-axle semi-trailers; seven-, eight- and nine-axle B-Doubles; PBS-approved A-Double and PBS-approved dog trailer combinations.

A common feature of milk tanker combinations is the Kompensator trailer coupling and most non-tanker drivers won’t have come across one of these. Because tanker bodies are torsionally stiff, with no ‘give’ over uneven surfaces it’s necessary to provide some flexibility in the truck’s fifth wheel connection, to prevent twisting forces causing the tanker bodywork to crack over time.

The fifth wheel ‘legs’ of the Kompensator are mounted on ramps that allow limited lateral and upward movement, countering centrifugal force and helping resist roll-over forces. Also, the assembly is mounted on a ball-race turntable, so that the resistance provided via the legs is constant, regardless of the articulation between truck and trailer.

As with nearly all road tankers, milk collection tankers are fitted with baffles, to restrict fore and aft movement of liquid. The typical milk tanker has a ‘spill-over’ bulkhead in the forward third of its volume, that fills first, to put weight over the drive or dolly axles. When that compartment is full, milk spills over into the rest of the tanker.

The NTI/NHVR engineering research included fitting cameras into milk tanker interiors, to see in real time just what was happening. The program also involved roll-over potential for different loading percentages.

The investigation showed that sloshing and surging presented the greatest risks to vehicle stability when the tankers were 40 to 70 per cent full. If a vehicle is in this load range and on a high-risk road section, it is significantly more challenging for the driver to maintain control of the combination.

That load movement situation showed up in NTI’s data on major incidents, showing critical differences between dairy tankers and all other unit types.

The most significant difference is the frequency of ‘inappropriate speed’ crashes that are predominantly single-vehicle, ’un-tripped’ roll-over crashes. Note that the leading cause is ‘inappropriate speed’, not ‘breaking the speed limit’. With highly dynamic loads, milk tankers can crash at relatively low speeds.

Dairy tankers crash differently from other unit types. NTARC’s data show that the leading causes of single-vehicle un-tripped rollovers for dairy tankers are inappropriate speed (32 per cent), inattention/distraction (20 per cent) and not at fault (16 per cent).

For other unit types, the leading causes are inattention/distraction (16 per cent), inappropriate speed (13 per cent) and not at fault (12 per cent).

Slosh, in particular, can elevate crash risk, because it raises a tanker’s centre of gravity and generates significant centrifugal force, pushing the tanker outwards on a curve. It is particularly dangerous when a tanker is around half full (40 to 70 per cent), when the load has significant mass and room to move.

High-risk roads for milk tanker roll-overs are narrow, winding roads, with successive or tightening bends and at roundabouts and freeway on- and off-ramps, where closely-connected sequences of left-right-left bends are common.

Another critical difference in the dairy tanker crash data is the proportion of single-vehicle crashes: 80 per cent involved the tanker only, compared with 59 per cent for all unit types. This difference likely reflects tankers’ operating environment, with lower traffic exposure than other freight tasks.

Dairy tanker crashes occur earlier in the day than for other unit types, because farm pick-ups are mainly in the first half of the day.

Schedulers and managers should consider dairy tankers’ sensitivity to changing load dynamics and ensure they allow drivers enough time to safely pick up and transport their loads, NTI asserts. Drivers should understand how slosh and surge affect their vehicles’ and combinations’ dynamics and adjust their speed accordingly.

NTI’s Transport Research Manager, Adam Gibson and other road transport professionals appear in several training brochures and videos that illustrate the unique challenges facing milk tanker drivers.

One video shows the varying swept-path characteristics of different vehicle combinations, including graphic proof of the excellent manoeuvrability of PBS designs that have steerable axles.

Probably the scariest videos cover the real-world behaviour of milk in a part-filled tanker. The degree of weight transfer fore and aft and from side to side explains why erratic handling can be experienced at relatively low speeds – around only 20km/h.

Adam Gibson uses a model tanker combination to show clearly the effects of surge on stability. The model tanker is made of clear material, so it’s easy to see in scale the movement of milk inside the tanker.

NTI has produced safety posters in pdf format and all the video training material is available free of charge here.