Speed management should form part of the overall risk management approach that mining operations should have in place and actively promote.
The aim of speed management is to minimise risks with driving at speeds that are inappropriate for prevailing conditions.
This can be achieved by establishing safe speed zones and developing measures to ensure compliance with speed limits.
It is important to create a traffic environment as similar as possible to conditions that drivers encounter on the public road network, it should be recognised that drivers have been trained and conditioned to follow the rules and regulations that apply on public roads.
Consequently, drivers will best know how to behave and respond to traffic inputs if they are familiar.
Australian Standard AS 1742.4:1999 Manual of uniform traffic control devices — speed controls should be referenced when determining appropriate speed limits on mine sites.
According to the Standard, some principles to consider are:
- speed limits shall be capable of being practically and equitably enforced by use of speed zones of adequate length, by limiting speed limit changes and by clarity and frequency of sign posting — in other words, not too many changes in speed limit over a short distance;
- the speed limit shall not be so low that a significant number of drivers will ignore it;
- speed limits shall not be applied specifically for the purpose of compensating for isolated geometric deficiencies — in other words, build well-designed roads so that low speed limits do not have to be used to compensate for design faults (e.g. corners that are too tight); and
- all signposted speed limits shall be in multiples of 10 km/h. When determining appropriate speed limits on mine sites, the following points should be considered.
The function and purpose of a road will provide some guidance as to the likely speed limit that drivers would expect to see.
In addition to set speed zones, advisory speed signs can also be used at specific locations on sealed roads to indicate to motorists that a reduced operating speed is more appropriate.
Examples include curves, steep crests or where the road conditions ahead dictate the need to drive at a lower speed.
Advisory speed signs are not mandatory and only provide advice to the motorist at that particular location.
They cannot be used on unsealed roads because of the variation of the road surface, hence the speed environment cannot be guaranteed.
The speed environment is determined by the elements of the road and traffic environment that influence a driver’s perception of an appropriate operating speed.
The road’s crash history should be taken into account when assessing the appropriate speed limit.
The Australian Standard governs the determination and setting of posted speed limits on public roads. The road environment on mining operations is somewhat different.
The main distinction is that a mine site is a controlled environment where the asset owner, in this case the mining principal, may assert its own controls, procedures and limitations over the traffic.
A good example is the issue of posting speed limits on unsealed roads.
The Standard recommends that speed limits or advisory speed signs are not applied to unsealed roads because the characteristics of unsealed road surfaces change significantly with variations in weather conditions, through watering or due to effects of traffic.
It cannot be guaranteed that a safe speed at certain conditions will be a safe speed if conditions change.
In practice, however, unsealed roads on mine sites are commonly provided with speed limits.
This is deemed to be appropriate as mine management has the legislative responsibility to ensure that work areas, such as roads, are safe.
Establishing speed zones
Set speed limits to provide a reasonable balance between an acceptable level of service and the driver’s perception of the road environment.
Speed limits should be logical, safe, practical and achievable, and reflect the condition of the road infrastructure to which they apply.
By imposing a speed limit lower than what the road configuration allows, some drivers will disregard the posted speed limit and drive at a speed that they perceive as appropriate.
Speed limits below 10 km/h are hard to comply with and not measurable by vehicle speedometers.
Such impractical limits convey the wrong message to road users.
It is important to minimise the number of speed limits within an area to three or four (e.g. 10, 20, 40, 60 km/h).
An important aspect of speed management is to consider stopping distances.
The stopping distance is the distance that a vehicle travels from the moment the external stimulus is within a drivers’ field of vision to its complete stop, in a safe manner.
It comprises the reaction distance (related to reaction time) and braking distance.
The reaction time depends on factors such as physical or psychological state of the drivers, available lighting and distractions.
The braking distance is determined by the vehicle type, operating speed, longitudinal friction factor and longitudinal grade of the road.
It is commonly understood that reducing speed has a positive effect on traffic safety.
Even at what are perceived as low speeds, such as 60 km/h, the reduction in stopping distance between 60 km/h and 40 km/h for cars is 32 m, which can make a huge difference between a vehicle being able to stop safely and being involved in a crash.
On the other hand, it is recognised that vehicle speeds play an important role in productivity and production results, especially for operations that depend on tight trucking cycles such as direct ore feed.
For such situations, it is suggested that the safety aspects of various operating speeds be carefully considered together with implications for production.
Separating light vehicle movements from heavy vehicles will significantly reduce the risk of vehicles being involved in incidents and the speeds on the roads can be set accordingly.
Signing speed zones
Speed limit signs should be erected on the left side of the carriageway.
Ideally, speed signs should be installed in pairs on both sides of the road when a change of speed zone is required and, normally, no other sign should be erected on any post carrying a speed limit sign.
It is also suggested that speed signs used on mine sites should be Size A, which is the largest legal sign size in Western Australia (i.e. used on freeways).
On long stretches of road, repeater speed signs should be erected at regular intervals of 500 m or less if necessitated by prevailing conditions.
Speed zones maps are a useful tool to familiarise drivers with an operation’s speed environment.
They should be used for driver training, advising drivers of any speed limit changes, such as temporary speed limits during road works, and re-installing signs that have been damaged and removed.
The maps should be updated whenever speed limits are changed.
High pedestrian activity areas
Special consideration should be given to areas with high levels of interaction between pedestrians and various vehicle types, such as car parks, administration areas, workshops and processing plants.
Implement a low speed limit environment to ensure the traffic risk at such locations is minimised.
The speed of 10 km/h is generally accepted as a safe speed for areas of high levels of interaction between vehicles and pedestrians.
This speed limit is usually used in public ‘shared zones’ such as malls.
Pedestrians hit by a vehicle travelling at this speed are less likely to suffer significant injury.
The low speed also reduces the possibility of contact between the vehicle and pedestrians.
This speed can also promote walking as the preferred transportation mode and reduces reliance on vehicles for transportation needs
A comprehensive speed management strategy is only partly achieved if there are no effective measures in place to ensure compliance with the requirements.
Site management can implement a number of measures to work towards lowering the risks associated with speeding and unsafe driving behaviour, and encourage compliance with the applicable road rules.
Such measures include procedures, engineering modifications and behavioural modification.
The following list of possible measures is by no means exhaustive:
- Establish realistic and simple speed zones that are easy to comply with.
- Enforcement and disciplinary actions should be used as a last resort measure to show management considers speeding to be an unnecessary risk-taking behaviour that will not be tolerated.
- Regular activities should be undertaken to promote the importance of compliance with speed limits and the serious consequences associated with speeding.
- Engineering measures can be used to physically slow traffic (e.g. narrowing sections of roads, installing speed humps, using invehicle speed monitoring systems).
- Speed checks can be used to modify road user’s behaviour, either as random handheld radar checks or by using portable speed radars with variable message signs to give feedback to drivers about their speed.
For its part, mine management should to ensure that vehicles provided are fit for purpose, roads and road infrastructure are constructed and maintained in a safe condition, and there are no unsafe or impractical speed limits in place.
Mine management should also ensure that there are no work pressures that would require drivers to speed and the road environment is forgiving to those who make genuine mistakes and lose control of their vehicles.
*This article was first published in the Western Australian Department of Consumer and Employment Protection’s MineSafe Western Australia Magazine.
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