Keeping metro track in good condition

Metro authorities are increasingly using hi-tech methods to inspect and analyse track condition with a view to improving ride quality and rail longevity.

Track maintenance on urban metros can demand different techniques to those used on main line railways. Train speeds are generally lower, but traffic is often dense. Frequently there is a high proportion of running in tunnel, with access difficult and little elbow room when the engineers do undertake work.

However, forward-looking metro authorities are borrowing some of the high technology techniques being used on main line railways to improve track quality and boost productivity. To begin with, many authorities are seeking to improve their knowledge of asset condition. Many metros have relied on human track inspection, but with high-tech methods now becoming widely available it is becoming easier to undertake predictive maintenance and avoid condition-of-track speed restrictions.

For the past two years ImageMap from Chicago, USA and Wiener Linien, the Vienna City transport operator, have been developing track measurement systems specifically suited to tramway and metro track conditions. Earlier this year, Wiener Linien invited more than 150 European metro and tram operators to Vienna to view these new measurement systems and vehicles in operation. The Vienna metro is being measured with a new car equipped with ImageMap state-of-the-art rail and track measurement equipment which was produced by MAV (Hungarian State Railways).

In addition to the metro car, ImageMap track geometry equipment and rail wear optical inertial equipment has been specially adapted to operate on a city tram that has been equipped to measure both standard and grooved rail. ImageMap says that this is the first time in Austria that a track owner has selected a non-Austrian supplier for this type of track measurement equipment.

ATM, the urban transport authority in the Italian city of Milan, is another operator laying heavy stress on advanced inspection techniques on the city’s metro. The systems employed permit the on-line collection of rough data and their off-line analysis. Such analyses concern:

• The seven main geometric parameters to verify the route quality
• The rail profile wear
• The rail rolling level corrugation
• Superstructure control through video inspection

ATM employs advanced equipment from Speno and others to maintain the metro track in good condition.

Ultrasonic detection

While track geometry (the position of the track relative to structures) is often crucial on urban railways with tight clearances, another area that is attracting interest is ultrasonic inspection for flaws in the rail. For example, last year on the London Underground, a joint initiative by the two Public Private Partnership contractors Metronet Rail and Tube Lines saw the introduction of a road-rail Land Rover equipped with Sperry Rail ultrasonic equipment to detect rail defects. The vehicle tows a trolley fitted with the equipment to identify track irregularities.

The new vehicle represents a substantial productivity improvement compared to manual methods. A comparison of old and new methods is enlightening. Using Sperry roller search units (‘walking sticks’), a team of three or four workers can inspect around 5km of rail in a four-hour night shift. The new ultrasonic Land Rover travels up to 15km/h and can cover 20km during an engineering hours shift, quadrupling the distance tested.

The Land Rover and trolley ‘roller service unit’ can detect defects in the rail web, including bolted joints, insulated rail joints, switches and crossings and defects that originate from the rail foot once it extends into the area under the web. This latter instance was the cause of a derailment of a London Underground train at Hammersmith in October 2003.

The Land Rover is being used on the open track sections of the Underground, which account for more than half the LU network. A number of modifications have been incorporated for the Underground, including a dead man’s handle, LU-pattern train stops, external emergency stop buttons, closed circuit television for a view to the rear and changes to clearances because of the Underground’s two electric rails. The work was carried out to meet the operating safety case of TransPlant, the plant division of Tube Lines, which supplies plant for most of the LU network.

The new system ultrasonically inspects, creates, displays and stores data from both rails simultaneously and can detect the full range of rail defects during one inspection. In addition, rail depth can be measured every 5mm along the track, identifying rail wear and corrosion. While the manual ‘walking sticks’ rely on operatives to register defects as they go along, the new vehicle gives a record of the run which is scrutinised within 24 hours. Records are being built up of each section of track, as frequency of inspection increases.

The PPP contractors say the greater frequency of runs will enable management of the rail asset to be much more scientific, with development of planned removal of defects, causing less disruption to passenger services. Metronet is working with the American decision support specialist Zetatech to develop a risk-based model of the history of defects, enabling increased testing frequencies in higher risk areas. For example, the north section of the Circle/ Metropolitan Line, under the Euston Road, has particularly heavy usage and inspection can be concentrated here.

The ultrasonic test road-rail vehicle on the Underground is an interim measure to improve the frequency and quality of track inspections while Metronet and Tube Lines develop an automated inspection train that can run during passenger service, costing in excess of £3 million.

A key requirement of extending inspection to deep tube lines is train location, as the satellite-based Global Positioning System used on the surface is not available. Doppler radar, electronic ‘tagging’ of stations and visual recognition are among systems being considered. The train will also add other complementary technologies such as track geometry, quality recording and heat imaging.

Lubrication

Enhanced inspection techniques are showing where rail and flange wear rates are particularly high and where metro authorities could usefully employ lubrication. For example, on the Circle Line in London, maintenance costs were high because a dirty ballast base gave rise to poor track geometry. Tight curves exacerbated the problem and on some sections rail was wearing very quickly. There were also reliability issues, as small particles of steel rubbing off the rail were affecting the insulation of the track circuits.

Intensified inspection, including the fitting of a video camera under a train to monitor how the track was behaving under the stresses of vehicles on it, revealed a number of problems. One was that lubricators were not dispensing sufficient grease. Engineers altered the dispensers, which mainly came from the British division of Portec of the United States, to dispense more grease.

More lubricators were installed to ease wear at critical points. Lubricators supplied by QHI of Australia, the design of which means the amount of grease dispensed is independent of train speed, were installed at the approaches to stations, where there had been a problem in getting sufficient grease on to the track. Another design, supplied by British company R. S. Clare, has low maintenance requirements – a useful feature on the tube, where access is difficult.

The improved lubrication regime employed on the Circle Line has resulted in reduced rail wear rates and longer intervals between rail replacements. The techniques employed on the Circle Line are now being used on other parts of the London Underground network.

Rail grinding

On main-line railways, rail grinding has been found to be a very effective method of controlling rail defects by grinding out flaws in the surface of the rail before they have time to develop and spread down into the rail web. Metro operators, too, are increasingly finding this a useful technique. For example, Metronet Rail in London is using a rail grinding machine to improve track quality and reduce noise on the Victoria, Bakerloo and Central Lines.

The machine, manufactured by Schweerbau, is designed to operate within tight tunnel clearances and around sharp track curves. Two grinding units, each with four grinding stones are towed by a manually driven 400kW diesel power unit.

The grinding units are computer controlled using settings for the depth of grind and angle of the wheels inputted by the grinding operator. Continuous feedback on the progress of the grind is provided to the operator so adjustments can be made depending on the condition of the rail head.

In tandem with rail grinding, wheel re-profiling is usually employed to maintain the wheel/rail interface in optimum condition. Many authorities have invested in wheel lathes from suppliers such as Hegenscheidt with a view to keeping metro train wheels in good condition and reducing wear on the rails.

For example, last year Tube Lines awarded a £2.1 million contract to Birse Rail for the design and construction of a wheel lathe at Northfields depot on the Piccadilly Line. The lathe is capable of reprofiling wheelsets without removing the axles. The project has involved the creation of the lathe together with associated building, mechanical and electrical works.