More stringent European safety regulations now stipulate that new railway tunnels have to be designed as two separate single-track bores. Furthermore the track system must take into account the need for road vehicles to access the line in case of emergency. Double-track tunnels currently under construction are also being built with such vehicular access in mind.
Tracks with this facility reduce the risks to which passengers are exposed when escaping along the line and allow them to do so without help from other parties. The almost completely closed surface of slab-track makes walking in a tunnel considerably safer, providing better underfoot conditions with the danger from protruding rails minimised.
It is for these reasons that RAIL.ONE’s RHEDA 2000® ballastless track is a particularly attractive system for existing tunnels of any length. In evacuation situations, it increases by many times the inherent safety of sections where it is installed and is effectively equivalent to the line being in the open.
So far, RHEDA 2000® has been adopted in more than ten countries on over 2,600km of railway, as well as incorporating around 150 turnouts and rail expansion joints. The road vehicle access system for this ballastless track has been designed to accommodate passenger cars and lorries, and has no adverse operational impact. It is rated for vehicles with axle loads of up to 10 metric tonnes.
Another stipulation of the tunnel regulations demands that the access system is designed to take sufficient account of the lifting forces – pressure and suction – exerted on the track surface by passing trains, rated at 5.3kN/m2.
Road vehicle access system
The system comprises small, individual components made from reinforced or fibre concrete. These cover 90% of the track, with their top surface 50-60mm lower than the rail head. Space around their edges enables visual inspection of the track supports without the system having to be disassembled.
With RHEDA 2000®, the precast units are not only located in the four-foot but also in the six-foot on double-track routes as well as between the cess rail and trackside path or other components installed along the sides of the tunnel.
In the four-foot, the units are triangular and pairs interlock to provide direct contact support, eliminating any hollow space beneath them as well as preventing rocking or tilting. Each one rests on three support points on the sleepers beneath the rail pad. The supports are in the form of pre-stressed bolt-spring connectors. These ensure the elements cannot displace vertically – which would otherwise result from the lifting forces of a passing train – and allow for precise position levels with respect to the rail head. The horizontal transfer of force takes place exclusively from positive geometrical locking between the elements and sleepers.
The rectangular outer units are installed over the track concrete layer where their distribution provides uniform transfer of the loads applied by road vehicles. They rest on two neighbouring sleepers and two integrated supporting bolts – these are height-adjustable to ensure the correct vertical level between the rail and trackside path, as well as ensuring a flat transition for vehicles driving onto them.
Quick and simple
RAIL.ONE’s road vehicle access system for RHEDA 2000® is highly adaptable and the vehicle access elements remain independent of the track they occupy. The system can accommodate the full range of the road vehicles you might expect to find on the railway. It can be assembled and removed quickly, and demands little in the way of maintenance.
Post-installation adaptations are possible to reflect changes in safety regulations or modifications that need to be made to the permanent way, such as derailment protection, new signalling equipment or safety systems. No special planning is needed to incorporate the system – expertise is already in place for the well-known RHEDA 2000®.
Plans to conduct trials of the vehicle access system under live railway conditions are being developed and these are likely to take place in the near future.