Types and Structure

This chapter discusses the types and structural features of high-speed railway turnouts in terms of structural composition, classification, technical requirements, and features of high-speed turnouts. In this part, high-speed turnout technologies are briefly explored, with examples of turnouts in three nations: France, Germany, and China. In addition, developments in other nations such as Japan and the United Kingdom are also introduced.

Keywords

Structure of high-speed turnouts; type of high-speed turnouts; technical requirements for high-speed turnouts; technical features of high-speed turnouts; high-speed turnouts in France; high-speed turnouts in Germany; high-speed turnouts in China

A turnout is a trackside installation enabling railway vehicles to change tracks or crossover another track. It is an essential part of a railway track system. In fact, a turnout is an integrated system. It is difficult to maintain and critical to riding speed and safety. In addition, it is regarded as the weak point of a line and a main concern in high-speed railway (HSR) construction [1,2].

1.1 Main Types [3]

High-speed turnouts refer to the turnouts for 250 km/h and above in the main line. Among these turnouts, those for 160 km/h and above in the diverging line are known as high-speed turnouts in the diverging line, which have greater numbers and longer lengths than other turnouts.

1.1.1 Composition

A high-speed turnout is composed of rails, sub-rail foundations (e.g., fastenings, ties, and ballast or ballastless bed), conversion equipment, monitoring system, turnout heaters, and track stiffness transitions at two ends [4].

It is generally designed as a simple type crossing owing to the structural complexity, that is, consisting of a set of switches, crossing, and transition lead curve.

1.1.2 Classification

Main types:

1. Turnouts for 250 km/h and 350 km/h in the main line.

2. Turnouts for 80 km/h, 120 km/h, 160 km/h, and 220 km/h in the diverging line.

3. Turnouts in the main line, the crossover, and the connecting line (by function). The turnout in the main line lies at the throat of a station, enabling trains to access the receiving-departure track through the main line. The turnout in the crossover, as shown in Figure 1.1, lies away from the station throat and enables a train to switch routes between the up line and the down line. The turnout in the connecting line also lies outside the station throat and enables a train to change tracks between two HSR lines. The three types of turnouts are for 80 km/h, 80-160 km/h, and 120-220 km/h in the diverging line, respectively.

4. Ballasted turnouts and ballastless turnouts (by subfoundations). Ballasted turnout uses prestressed concrete ties; ballastless one may use embedded concrete ties or slabs. The two turnouts use the same rails.

5. No. 18, No. 30, No. 42, and No. 62 turnouts, etc. (by turnout number). In France and Germany, a high-speed turnout in the diverging line may have a nonintegral number (e.g., No. 39.113) when being laid in a line with varied track distances.

6. Turnouts with swing nose crossings or fixed crossings (by crossing type). All high-speed turnouts in China are provided with swing nose crossings, whereas in other countries, fixed crossings may be used in some turnouts for 250 km/h.

7. Turnouts with a rail cant of 1:40 or 1:20 (by rail cant). The rail cant of high-speed turnouts is 1:40 in both China and Germany, and 1:20 in France.

8. In addition, 60 kg/m rails, standard gauge, and trans-sectional continuously welded rail (CWR) track are quite common in HSRs, so high-speed turnouts are not classified by rail type, gauge, or joint.

Normally, a high-speed turnout is named after the combination of the rail type, the permissible speed in the main line, the sub-rail foundation, and the turnout number, such as No. 18 ballastless simple turnout with 60 kg/m rails for 350 km/h.

1.2 Technical Requirements

A high-speed turnout is an intricate system. It involves the technologies of track structures (rails, fasteners, ties, and ballasted and ballastless bed, etc.), interface technologies of CWR track on embankments and bridges, the wheel-rail relation, electrical conversion, and track circuit, as well as interdisciplinary technologies of precision machinery manufacturing, mechanized track laying and maintenance, control survey, and informatized management [5].

1.2.1 Excellent Technical Performance

A high-speed turnout shall meet the following technical requirements:

1. High speed
It shall have the same speed in the main line of the turnout as in a common railway section, and have a relatively high speed in the diverging line without affecting normal traffic. For safety considerations, the design speeds in the main line and the diverging line shall have safety margins of 10% and 10 km/h, respectively.

2. High safety
For a high-speed turnout, the following requirements shall be satisfied when an Electric Multiple Unit (EMU) train travels at the design speed in the main/diverging line:

a. Indicators such as load reduction rate and derailment coefficient are the same as in a section

b. The spreads of switch rails and swing nose rails are sufficient to avoid collision against wheels

c. The conversion equipment functions normally, so that no defective insulation area (where all traffic lights are red) or signal abnormalities occur

d. Moveable rails are locked securely, so that no derailment takes place in case any inclusion appears in the closed zones, or the switch rod is distorted by the inclusion

e. The monitoring systems are integrated to identify faults and hidden dangers degrading riding safety, such as abnormal conversion, inordinate closure, and rail fracture; and

f. Turnout heaters are provided in cold areas to prevent snow or ice accumulating at the switches and crossings in cold weather, so as to ensure normal operation.

3. High stability
When an EMU train travels at a normal speed in the main/diverging line of turnouts, the train will not shake significantly, thus providing the same passenger comfort in turnouts as in sections. The lateral carbody acceleration shall not have first-order inordinateness (i.e., 0.6 m/s2 as per the criteria of the planned preventive maintenance for Chinese HSR) during the passage of comprehensive inspection trains or track geometry cars in the turnout.

4. Excellent comfort
The same passenger comfort can be offered vertically as in a section, and no "jerking" (which may occur at bridge ends) occurs when an EMU train travels at a normal speed in the main/diverging line, nor does any inordinate vertical vibration appear due to inhomogeneous track integral stiffness in the turnout area. The vertical carbody acceleration shall not have first-order inordinateness (i.e., 1.0 m/s2 as per the criteria of the planned preventive maintenance for Chinese HSR) during the passage of comprehensive inspection trains or track geometry cars in the turnout.

5. High reliability
HSRs are in closed operation in the daytime, and occupied for "skylight" maintenance at nighttime. Therefore, high-speed turnouts shall have high reliability, without conversion faults or invalid closure detections, etc.

6. High smoothness
All HSR track structures, including high-speed turnouts, shall have high performance in smoothness. Geometric deviation (alignment, longitudinal level, etc.) and closure clearances of a turnout shall be acceptable. The scant switching displacement shall not affect the deviation of the gauge, and structural irregularities induced by wheel-rail relation shall not affect riding quality.

7. High accuracy
A turnout is composed of thousands of components; each component may have certain manufacturing errors. For high smoothness in assembly geometry and closure, the manufacture, assembly, and laying must be highly accurate (optimally 0.2 mm as per the criteria for planned preventive maintenance for Chinese HSRs).

8. High stability and less maintenance
A high margin of strength is required under the action of high-speed trains and temperature, etc., so that turnouts are less susceptible to large residual deformation, featuring higher structural stability and less maintenance.

9. Easy maintenance
With the increase in operation time, gross carrying tonnage, and deterioration of turnouts, tracks with inordinate irregularities or seriously damaged components shall be repaired or replaced immediately during the "skylight" period to resume normal operation in the shortest possible time. The structural design of high-speed turnouts shall facilitate future maintenance from practical and technical considerations.

1.2.2 High Cost-Effectiveness

The rails (switch rail, point rail, etc.) of a turnout will bear great wheel-rail force when guiding the wheels during conversion operations. Therefore, they are subject to wear...