1. UNIT IV TRACK CONSTRUCTION

2. POINTS AND CROSSINGS Point and Crossings are peculiar arrangement used in permanent way to guide the vehicle for directional change. Broadly point andcrossing assembly consists of three maincomponents namely Point, Lead and Crossing element

3. . A point consists of one pair of tongue rails and Stock Rails with necessary fittings.Crossing is a device in the form of V- piece introduced in the track to permit movement of wheel flange at the inter section of two running lines.It has gap over which the wheel tread jumps.The track portion between point and crossing is is called lead.

5. TURNOUTS Turnouts are called left hand or right hand, depending on the side, to which the rolling stock gets diverted. Similarly tongue, wing and stock rails are called LH or RH depending on their position, looking in the facing direction of the points

6. SIGNALLING A signal is a mechanical or electrical device erected beside a railway line to pass information relating to the state of the line ahead to train/engine driversrailway linetrain/engine drivers. The driver interprets the signal's indication and acts accordingly. Typically, a signal might inform the driver of the speed at which the train may safely proceed or it may instruct the driver to stop.

7. APPLICATION AND POSITIONING OF SIGNALS signals displayed simple stop/proceed indications. As traffic density increased, this proved to be too limiting and refinements were added. One such refinement was the addition of distant signals on the approach to stop signals. The distant signal gave the driver warning that he was approaching a signal which might require a stop. This allowed for an increase in speed, since trains no longer needed to be able to stop within sighting distance of the stop signal.

8. USES OF SIGNALS that the line ahead is clear or blocked. that the driver has permission to proceed. that points are set correctly. which way points are set. the speed the train may travel. the state of the next signal. that the train orders are to be picked up by the crewtrain orders

9. WHERE SIGNALS CAN BE PLACED at the start of a section of track.section on the approach to a movable item of infrastructure, such as points/switches or a swingbridge.swingbridge in advance of other signals. on the approach to a level crossing.level crossing at a switch or turnout. ahead of platforms or other places that trains are likely to be stopped. at train order stations.train order stations

10. INTERLOCKING In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings. The signalling appliances and tracks are sometimes collectively referred to as an interlocking plant. An interlocking is designed so that it is impossible to give clear signals to trains unless the route to be used is proved to be safe.railway signallingtracks

11. INTERLOCKING TYPES Mechanical interlocking Electro-mechanical interlocking Relay interlocking Electronic interlocking

12. TRACK CIRCUITING A track circuit is a simple electrical device used to detect the absence of a train on rail tracks, used to inform signallers and control relevant signalstrainrail tracks

13. CONVENTIONAL AND MODERN METHODS the sole train operator on the line, parallel double tracks were built for trains traveling in opposite directions, timetables were established and a crude signaling system was established to prevent collisions. These methods of operation became standard on railways across the world.double trackssignaling This speeded up the transportation of coal to the sea as the River Tees there was deeper.River Tees Further upstream around Stockton-on-Tees shallow waters greatly hindered shipping.Stockton-on-Tees In 1834 a rival line, the Clarence Railway, was also built for the shipping of coal, this branched off from the Stockton and Darlington Railway at Shildon and terminated at Haverton Hill and Port Clarence on the opposite side of the river to Middlesbrough.ShildonHaverton HillPort Clarence

14. MATERIALS USED. BALLAST Track ballast forms the trackbed upon which railway sleepers (UK) or railroad ties (US) are laid.railroad ties *It is packed between, below, and around the ties. It is used to facilitate drainage of water, to distribute the load from the railroad ties, and also to keep down vegetation that might interfere with the track structure.drainagevegetation *This also serves to hold the track in place as the trains roll by. It is typically made of crushed stone, although ballast has sometimes consisted of other, less suitable materials. The term "ballast" comes from a nautical term for the stones used to stabilize a ship.crushed stoneballast