Line capacity means the number of trains that can be run on a section in 24 hours.
Line Capacity is calculated in three different ways:
- Maximum Line capacity – This the maximum number of trains that can be plotted in the master chart so that it is impossible to introduce even a single train.
- Practical Line capacity – This is number of trains which can be run on a given section in practice. This can be derived from Maximum Line capacity by making allowances for maintenance of Permanent way, time required for operational exigencies/irregularities etc. In general in Railways Line Capacity means Practical Line Capacity.
- Economic Line Capacity - Following diagram shows Cost analysis against number of trains on a section.
- It can be seen that as the number of trains in a section goes up the cost of running trains decreases resulting in higher return upto a certain point. This is due to the better utilization of available resources. But as the number of trains goes higher than this point section get saturated making it increasingly difficult to increase train services without operational delays. Ultimately this leads to an increase in Cost. Optimum number of trains which can be run on the section economically (Point E in the graph) is called Economic Line Capacity.
Calculation of Line Capacity - Following are the commonly used methods for calculating Line capacity
1. Scott’s formula
Line Capacity C = 1440/(T+t) x E
Where T is the running time of the slowest goods train over the critical block section, T is the Block operation time and E is the Efficiency facto
2. Charting method
- Charting method is the most reliable method of calculating Line capacity. The train paths are plotted in a time-distance graph for 24 hours. Fist paths of all Scheduled Express/ Passenger trains are plotted. Then scheduled goods trains are plotted. And after other paths are plotted as many as possible in the chart.
- Line Capacity by charting is more accurate as this method takes into account all the peculiarities of a given section. It should not be less than the Line capacity as per Scott’s formula as it is based on the slowest moving train over critical section.
- In Indian Railways Line Capacity is calculated based on Charting method.
- A section can be considered saturated when it is running more than 90% of Line capacity arrived by charting.
- Terminal facilities should not be taken into account while calculating Line Capacity.
Increasing Line Capcity
- From Scott’s formula we can see that Line capacity increases, if we decrease Running time T, Block operation time t and increase the Efficiency FactorE.
- Reducing T - Can be achieved by reducing length of Block sections (provision of intermediate block stations etc.) or by increasing speed of trains.
- Reducing t - Block operation time can be reduced by provision of tokenless Block instruments, panel interlocking, automatic signaling etc.
- Increasing E - Efficiency Factor E can be increased by Time table improvements, improved maintenance practices ,improving staff efficiency, yard and terminal improvements, provisions of simultaneous reception, additional loops etc.