Traditionally, a significant proportion of switches and crossings (S&C) for UK tramway and urban railway systems (and for the mainline UK rail network) are manufactured from cast austenitic- manganese steel (AMS). This has been used owing to its good resistance to abrasion, high work hardening capacity on impact and excellent toughness following solution treatment and water quenching.
Following the passage of several million gross tonnes of traffic, AMS S&C can reach hardness levels of 500 to 550 HB. However, the time taken to reach optimum hardness depends on axle load and, for tram/light rail applications, is inevitably considerably longer than on heavy rail networks.
This variability, plus other drawbacks including the tendency for noise and vibration to be generated by the jointed connections used with AMS, has prompted VTS Track Technology to explore the use of alternative materials. VTS, through its parent companies Vossloh Cogifer and Tata Steel, is well placed to be able to bring to the UK market both proven technologies and methods and new innovative steel compositions.
Switches and crossings which are machined from rolled steel blocks have long been in use on tramway networks throughout continental Europe, and over the past several years VTS has pioneered their use into UK tramway systems with installations at Manchester, Nottingham and Croydon.
There are several different grades of steel which can be offered to the client dependant upon the frequency and tonnages of traffic. For example, at Piccadilly Gardens in the centre of Manchester both switches and crossings have been supplied in 400HB COGIDUR Material due to the high frequency of traffic. Elsewhere in Manchester, including at Media City, the crossings have been produced in a lower grade steel. There are also other long-life steels being developed by Tata Steel which will replace existing applications for crossings in both the light rail and heavy rail sectors.
Whichever steel is chosen, the switch and crossing will be supplied as a single unit. This will eliminate the need for fishplated joints which, in addition to causing noise and vibration, can lead to longer term issues of maintenance which can be particularly problematic for track embedded in the street.
Giving crossovers a lift
Recognition that noise and vibration and areas for concern in the urban environment have led VTS to introduce the lift over crossover which has, to date, been installed at Nottingham and Manchester and is designed to remove rail discontinuities.
In the case of the Nottingham installation, trams passing over the turnouts on the Royal Centre crossover (between the northbound and southbound tracks outside the Theatre Royal in the centre of Nottingham) were causing unacceptable levels of noise and vibration inside the theatre. To reduce the peak level noise produced by the trams passing over the crossing, all rail discontinuities (associated with traditional fishplated cast manganese crossings and wheel transfer across the throat area of the crossing) needed to be removed.
A lift-over crossing allows trams passing in the through directions to travel at speeds of up to 30 km/h on the plain rail with no rail gaps. Trams using the crossover to traverse tracks must pass over the through rail on their flanges at a reduced speed not exceeding 5 km/h.
Using a lift-over crossing made the vibration go away, and now nothing can be heard inside the Theatre Royal. It worked as traffic predominately uses the through route – only using the crossover road during emergencies or engineering works when the reduced- speed lift over crossing is more than adequate.
The crossing block for the Royal Centre crossover was manufactured from COGIDUR 1300 N/mm2 grade weldable steel. The abutting closure rails were then welded to the crossing block in the workshop to eliminate joints.
The switches are of grooved type and are also manufactured from COGIDUR monoblocks. They have been supplied with maintenance- friendly, removable switch blades (also in COGIDUR steel) that can be changed easily. The switches were alumino- thermic welded to the closure rails in the factory and the layout was supplied in two large sections (held to gauge by tie bars) to minimise on-site welding during the installation process. The only site welds that were required were between the two turnouts and at connections with the existing rails. Both switches were also provided with Hanning and Kahl HWU 40D manually-operated switch mechanisms. These were fitted and fully integration-tested before delivery to site.
The versatility of using rolled steel blocks rather than AMS also allows for other solutions to be implemented that reduce the ‘squealing’ noise associated with traffic on tight curves which complements other extensive noise reduction systems available from both Vossloh Fastening Systems and Tata Steel.