Metros present a unique environment as a combination of underground and overground track. The frequency of train passage is significantly higher than mainline railways and it is theoretically possible to accumulate a large volume of historic data for the same track section over a short period of time. Given fixed capacity issues, track possession tends to be difficult and there is hardly any time between trains to carry out inspection. It is a typical misconception that Metros do not have the same level of track defect issues as mainline or freight networks. The shear forces between rail and wheel are much higher because of high curvature with higher train passage frequency. Consequently, the rail-wheel interface becomes a very significant issue. Poor rail grinding and poor track geometry can easily lead to excessive track load on specific rail sections, causing major damage to the rail in terms of rail breaks, corrugation, shelling, weld fractures, and rail head and wheel flats. The wheel damage on metro networks is much more pronounced, requiring frequent wheel reprofiling that reduces its life. Despite lower speeds of travel, generally <100 km/hr, the level of noise and vibration remains very high, and wheel flange wear is significant because of high track curvature. Metros also lay a greater emphasis on issues that affect rolling stock, e.g. tunnel clearances, overhead line inspection, third rail issues and noise and vibration that may affect residents or passengers that may not be the highest priority for mainline railways. Even though Metro tracks are of smaller length, less than 3 hours daily are available for any repairs of track walking which is wholly inadequate. Several diagnostic measurements cannot be made through human eyes, e.g. track geometry or early stage defects such as newly developing rail fractures, which makes diagnostic automation very important. Currently most Metros use handheld tools for measuring wheel and rail profiles and track geometry which is supplemented by regular track walks. Unfortunately, given time constraints, track measurements are often only made in curve sections or in limited areas as opposed to the entire track, as each measurement may take up to 15-20 minutes, and measuring over say 50 meter section can take up an entire 3 hour session.

Metro networks often include tunnels which mean that defect positioning cannot depend on GPS. Wheel encoder based distance measurement coupled with regular synchronisation against known landmarks is important. In the future, given the short route sizes associated with Metros, it will become possible to use a combination of various highly accurate track positioning technologies that are costly for mainline railways (for example RFID). Given short distances involved, regular repeat runs of the track can quickly build a very detailed understanding of track quality at all times.

In a recent survey by Rail Vision of a leading metro system, looking at 450 incidents that caused major delays across two year period, the following defects and their frequency of occurrence were noted.

1. Damaged switch blades (Included in 1% defective switch and stock rail)
2. Damaged or loose stretcher bars (Included in 3% loose components)
3. Defective block joints. Mainly rail rolled over the T piece (end post) and metal debris on the T piece (30% defective block joints)
4. Signal track wires distressed or displaced (28% broken bonding wire)
5. Broken rails (8% broken rails)
6. Rolling contact fatigue (Included in 1% WRI)
7. Squats and wheel burns (Included in 1% WRI)
8. Missing keys and clips (Included in 3% loose components)
9. Loose and missing components (Included in 3% loose components)
10. Lubrication and grease build-up (Included in 8% build up of grease /fluff)
11. Cracked, damaged or arcing insulator pots (Included in 7% defective insulator pot.)
12. Obstruction in train stops (3% obstruction under train stops) 
13. Stock rail bolts (Included in 3% loose components)
14. Dipped and battered joints (Included in 1% WRI)
15. Lipping (Included in 1% WRI.)
16. Build-up of debris (Included in 8% build up of rubbish)
17. Corrugation Amplitude (mainly) and wavelength are required.

The above study provides some insight into maintenance issues important for metro networks.

RV Diagnostics

Rail Vision provides a range of diagnostics suited for metros with systems that can be mounted on passenger trains. A system can easily cover all metro lines that the train can travel on. Our integrated TrackVue Z series systems can measure track geometry, rail wear, vehicle dynamics and rail wheel interaction parameters while at the same time performing complete visual inspection with line-scan cameras. The following slide-show presents typical metro rail track defects detected by TrackVue product series Z.

A slide-show of metro railway track defects

RV Advantage

The main advantage of using Rail Vision products for metro railways includes:

  • We have extensive experience of working on Metro networks in India and Singapore. We bring a wealth of experience from these operations having installed diagnostic systems on passenger trains.
  • We have solutions for use on both maintenance vehicles and passenger trains. The solutions for passenger trains do not use any in-cabin space for our equipment.
  • All of our systems can be operated remotely and are therefore invisible to the train driver and passengers
  • Our systems work at speeds of up to 100 kmph, typical of such networks providing high quality image resolution compared to any other vendor (< 0.33 mm/pixel) and with 20 cm sampling distance for rail wear and geometry measurements
  • We are able to pull together data from multiple sensors to explain the root cause of problems, e.g. excessive or one side track and wheel damage and we re able to provide a range of data post-processing tools and services for predictive maintenance.
  • We offer cloud based data management services to reduce IT burden on customer organisation