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the rail engineer • November 2013
Fitting more brakes PAUL CONWAY
O
n-track plant, mostly construction equipment which has undergone a road-rail conversion, is very common on the railway infrastructure. There are various types of conversion, each of which has its advantages and disadvantages. Back in issue 89 (March 2012), The Rail Engineer reported on a Network Rail initiative to fit direct rail wheel braking (DRWB) to approximately 450 excavator-based machines by means of automotive-style disc and calliper brakes.
High-ride excavators The program followed serious ‘failure to stop’ incidents reported on by the RAIB (Rail Accident Investigation Branch) at Raigmore near Inverness and Rannoch Moor involving two variants of 9b high-ride excavator. These are vehicles with rail wheels which, when deployed, jack the rubber-tyred road wheels up clear of the railhead. Instead, the tyres impinge on the rail wheels, imparting drive and also braking. If for any reason the tyres do not contact the rail wheel properly, then there is no drive but also, more importantly, no braking. As an immediate response to the two incidents, Network Rail undertook a risk assessment of the use of 9b RRV equipment to maintain and renew the infrastructure, the output of which was proposed gradient restrictions and a medium term plan to upgrade machines with brakes that act directly on the rail wheels. Subsequent discussion with the ORR (Office of Rail Regulation) resulted in the enforcement of the gradient restrictions by way of an Improvement Notice which held Network Rail to its declared braking plans. The upgrade program saw Network Rail contracting with a number of the established vehicle converters rather than just one, to ensure maximum capacity in the market and hence achieve the throughput of machines to satisfy the regulator with the rate of upgrade in response to the improvement notice. Each converter submitted designs for review and evaluation by Network Rail Plant Engineering against the remit. Once the commercial process was complete and contracts were in place the upgrade programme began with the successful companies, Rexquote, GOS Engineering and Alan J Hargreaves Plant.
LOIs In parallel with the upgrade programme, the risk of ‘failure to stop’ incidents was contained with a number of control measures as briefed out in a Network Rail Letter of Instruction (LOI) NR/BS/LI/235 including: 1. Restriction of use of 9b machines on gradients equal to or greater than 1:75; 2. Planning hierarchy to select 9a or 9c machines as a first choice; 3. Use of trailers with service brakes to enhance system braking; 4. High Ride checks to ensure an optimal interface between road and rail wheel. The LOI was phased in its approach, mandating the 1:75 restriction on six Delivery Units (DUs) initially and so addressing those with the greatest population of steep gradients. These were Perth, Glasgow, Plymouth, Cardiff, Motherwell and Shrewsbury. The use of service-braked trailers (point 3 above) is an important point to note. The owners were encouraged via the Rail Plant Association and other industry forums to upgrade their trailer fleets to incorporate service brakes with many owners choosing to fit hydraulic and pneumatic solutions to give maximum flexibility and compatibility with host RRVs. Around.80% of the national fleet has now been updated and another LOI will remove the remaining park-brake-only variants from Network Rail’s infrastructure at the end of March 2014. The upgrade of machines was regularly reviewed against plans to ensure that the volume of machines available to work on gradients met the intent of the LOI to minimise business impact and reduce system risk.