General principles - site traffic control
Site traffic control relies upon a combination of physical features such as the selection of appropriate vehicles to carry out the necessary work in the conditions that prevail, road layout and marking, signs and signals and other considerations such as systems, procedures and training.
Site traffic control should typically consider the following types of traffic:
- Road traffic - commercial delivery vehicles (including road tankers, wagons, couriers etc), internal vehicles (including fork lift trucks, mobile cranes, bicycles), visitor and staff cars/motorbikes/bicycles etc;
- Pedestrian traffic - site employees, contractors and visitors either on their way to or from their normal place of work at the beginning or end of the working day, or as part of their work during the day.
Road users, both drivers and pedestrians, should know exactly what is expected of them. This can be achieved by establishing a Road Hierarchy, which is used to provide a consistent standard for each road type in terms of design standard, signing, access constraints etc.
Traffic routes should be determined and can be classified as either access/through routes to site for deliveries, shuttle routes between buildings for on-site activities, or emergency access routes for fire engines, ambulances etc. Careful planning and consideration of site traffic control issues can result in a reduction in the likelihood of collisions between vehicles and/or equipment.
Incompatible types of traffic should be segregated as far as possible to avoid potential interactions between chemicals in the event of a collision between road traffic vehicles or between road traffic and stationary storage facilities or pipelines carrying chemicals.
This guidance is not concerned with traffic control within buildings such as warehouses or process plant areas where special consideration needs to be given to the potential interaction between fork lift trucks and/or pedestrians.
Traffic flow
In order to assist in controlling traffic flow on-site a number of additional measures can be incorporated in order to manage traffic flow in congested areas and reduce speeds on-site. Such techniques include the following:
- Traffic lights can be used to control flow at busy junctions, in narrow locations and at entry and exit locations to the site;
- One-way systems should be considered where necessary to reduce the likelihood of collision, reduce congestion and improve traffic movement;
- Roundabouts may smooth traffic flow and avoid road traffic turning directly in front of on-coming traffic;
- Traffic calming devices such as speed humps, rumble strips, width restrictors etc can be incorporated into road design to encourage a reduction in speed. (Such devices are not appropriate in areas where fork lift trucks routinely operate since they introduce additional hazards for this type of vehicle). The design of such features must be appropriate for the type of traffic envisaged;
- Physical barriers should be incorporated into road design to protect vulnerable and hazardous installations such as storage tanks, pipework systems, buildings or pedestrian access areas;
- Signs and road markings; and,
- Site speed limits.
Site based immobilisation systems
A variety of different site based schemes can be considered for immobilising vehicles and ensuring safe operations during loading/unloading procedures.
In the simplest form, chocks can be positioned beneath the wheels of the road tanker in order to immobilise the vehicle. The chocks will provide some form of resistance against road tanker movement in the event of any attempt to move the vehicle. There is the possibility that the chocks may not be removed when the loading operation has been completed leading to problems.
Removing and retaining the road tanker vehicle keys in a control room or remote location can also be considered.
However, such systems rely upon manual intervention and may not therefore be relied upon.
Other systems for dedicated loading/unloading facilities may involve automatic barriers that should be lowered before the offloading/loading valves can be operated. These barriers can be automatically interlocked through a computer system (DCS or similar) to the operation of the loading valves or interlocked via a physical system (key interlock system or similar). Motion detectors attached to the vehicle can also be used.
The advantage of these systems is that they are owned and maintained by the site and are therefore directly under the control of the site.