Signal set to go

The words 'signal failure' can make the blood of many travellers boil as they know their journey to work or home is going to be a lot longer than anticipated.

One common cause of this commuter nightmare is faulty track joints that short out signals and falsely indicate the presence of a train in the rail section.

While we in the UK have grown accustomed to complaints about our train service, one Canadian rail-fastening company thinks it might have come up with the solution to relieving rail woes, though it is yet to be taken up in the UK.

NorFast has developed a breed of insulated joints made of tougher, modular components which promise to cut down on rail line maintenance and delay times. The joints are made of a combination of thermoplastic polyester and an elastomer that can be installed without in-track welding. The product, called NIJ-6 Hercules, would replace steel joints, which are bolted and glued into the middle of the rails with epoxy resin.

Insulated joints play an important role in current railway circuit-based signal systems, but the epoxy resin traditionally used to affix them can introduce weak points in the rail that can lead to signal failure or potential derailment.

Insulated joints divide track into electrically isolated, two to five-mile segments that detect train presence and activate trackside signals. When an epoxy de-bonds it can cause the bars or bolts in the joint to make contact with the rails and short out the signal in each block, which then falsely indicates the presence of a train in the rail section.

These type of undependable joints, nicknamed 'glue joints,' were popular and effective when they first came out in the 1960s, says Paul Tucker, NorFast vice-president for operations.

'When glue joints came on the scene they were absolutely wonderful, but if you go back and look at what was happening on the freight railroads in the 1960s, probably one of the heaviest lines that you had would be 20-25 million gross tonnes (MGTs),' he said. 'As time went on, into the mid to late-1980s, tonnages, axle loads and frequency of trains increased, and the railroad line that ran 20MGT in the 1960s was all of a sudden running 100MGT, whereas the life of a glue joint runs somewhere from 175MGTs to 300MGTs.'