Tracking signal

Railway track signal syn. railway fusees or railway torpedo, warning signals placed on railway tracks that produce a loud report when crushed by the train. 

Tracking Signal—The ratio of the cumulative algebraic sum of the deviations between the forecasts and the actual values to the mean absolute deviation. Used to signal when the validity of the forecasting model might be in doubt. 

For example, in period 2 of Table 8.4, the forecast error is 10. The sum of the forecast errors to that point is 20 (period 1 + period 2). The MAD for the first two periods was 10. So, dividing the sum of the forecast error (20) by the MAD (10) gives a tracking signal of 2. This is less than the tracking signal critical value, so no problem is indicated in the forecast. 

Tracking signal A signal that forecasting techniques should be reevaluated. (Handbook of MRP II and JIT)... 

Forecasts are d5utamic and they are updated as more information becomes available. Hence, after selecting an appropriate forecasting method and the forecasts based on that method, it is important to continuously monitor the forecast accuracy. For this, one can use one or more of the forecast errors discussed in Section 2.9. In practice, another measme, called Tracking Signal, is also commonly used for monitoring forecast accmacy. 

Tracking signal Tracking signal at period k, denoted by TSt, is the ratio of Bias and MAD up to period k. hi other words. 

Unlike the forecast error defined in Section 2.9, tracking signal is not a single number. Instead it is a series of numbers, which can be used to detect changes in the pattern of the forecast. 

The generally acceptable values of TS are 6. When the tracking signals go outside these limits, the forecaster should be notified to determine the cause of fhese limit violations. 

Tracking signals outside the limits do not automatically imply that the forecasting method is not working. Environmental conditions, such as local economy, sales promotions, new competition, etc., can cause sudden fluctuations in tracking signals. 

Consider the data given in Table 2.9 (Example 2.11). Compute the tracking signals and plot. 

Institutionally, privatization replaced a unified vertical command structure with a complicated structure of some sixty independent businesses contracting with each other. Some of these had previous railway experience, others had none. The new structure separated the operation and the maintenance of the infrastructure from the operation of train services. At the centre of the new structure are the infrastructure controllers, the only widespread element in the new system (HSE, 1996 129) and important because they have been allocated central safety responsibilities (see below). Railtrack, which was set up in April 1994, is so far the only infrastructure controller and as such it owns and manages the track, signalling, and other operational infrastructure of the railways. The company is devolved geographically into ten zones. BR remains in operation to control those parts of the industry not yet privatized, so the company is effectively being slowly run down. 

Standardised safety requirements and safety targets are necessary to achieve full compatibility between trains, railroads (track, signalling, power supply, telecommunications, etc.) and operating rules. A nttmber of novel techniques, as well as extensions of existing techniques and tools, have been used to enable safety risk modelling as follows ... 

The insulation afforded by plastics materials with the poorest properties, such as polyamide 6.6 or plasticized PVC, is still more than adequate, except for the most critical uses. This is exemplified by the use of the former by British Rail as an insulant in automatic track signalling, and of the latter in domestic cable insulation. 

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