lesson 5 railway transportation signals.doc

Lesson 5 Railway Transportation SignalsHistory of Railway Transportation SignalsRailway transportation signal can be divided by sight signal and hearing signal. All of the drivers must obey it.Railway transportation signal are invented and developed in practice. At the begining, trains are leaded by workers who ride on the horse. In order to attract attention, they ware the black top hat and black coat and white trousers, use their hand as signal to conduct the train go ahead or stop. At that time the trains were in motion in daytime and the speed just 6 km/h-16km/h, and people can signal the train by using the horse. But it wasnt need long time for the numbers of trains and the speed increasing, horse can not catch up the train, obviously trains neednt signal which is at the trains back. So people strart to use the fixed signal to make the trains safety. When the trains run in the night, the red lights means the stopping and white lights means the movement. Genuine knowledge comes from practice, people recognize that rectangle light can be seen longer than other shapes. This discovery was use in London first. Red lights also means the stopping and because the white lights are easily mixed up with the civil light, the green lights instead of it. About Railway Signal A signal is a mechanical or electrical device that indicates to train drivers information about the state of the line ahead, and therefore whether they must stop or may start, or instructions on what speed they may drive their train. Signals are used to indicate one or more of the following: that the line ahead is clear (free of any obstruction) or blocked; that points (also called switch or turnout in the US) are set correctly; which way points are set; that the driver has permission to proceed; the speed the train may travel; the state of the next signal; Signals can be placed: ahead of points/switches; at the start of a section of track (with block signaling); ahead of a level crossing; ahead of platforms or other places that trains are likely to be stopped.Control and Operation of Signals The earliest signals were directly operated by a signalman on the basis of his knowledge of the line ahead. There was no mechanical check that the signal provided correct information. Later, signals were mechanically connected to the points that they protected, so that the signal could only be set to show a “proceed” indication if the points were in fact set (or set and locked) correctly. When multiple signals are used to control movements in the same area, the signals will also be connected together to prevent conflicting indications. These signals are said to be “interlocked”. For example, two signals facing trains approaching from opposite directions on the same track are interlocked so that only one of the two signals can show a “proceed” indication at the same time. A subsequent development was to connect the signals to devices that detected the presence of trains, so that a signal could not show a “proceed” indication when there is a train in the section of track protected by the signal.Early Signals In early years of last century, timetable and train order operation still has some significant flaws, such as an over-reliance on the ability of the crew of a stranded train to let other trains know of the problem, and a general intolerance for human error. When everything goes perfectly it works well, but mistakes are easy and deadly. Timetable and train order is only suitable for railway lines which carry relatively little traffic, and is unworkable on busy rail lines because it requires great separation between trains. Where this is the case, physical signals need to be used (either mechanical semaphore signals, or-more commonly in the modern era-electric light signals ) to show the train crew whether the line ahead is occupied and to ensure that sufficient space is kept between trains to allow them to stop.Blocks If two trains cannot be running on the same section of track at the same time, then they cannot collide. This notion forms the basis of most signaling systems. The rail network is divided into sections, known as blocks. Two trains are not allowed to be in the same block at the same time. A train cannot enter a block until it is permitted, generally by a signal that the block ahead is empty. on high-speed railways, block signaling has disadvantages because the required block length to safely stop a train would severely decrease the lines capacity. Also, signals become increasingly hared to spot and recognize at