Section Capacity and Throughput
Definition: Line capacity is also known as section capacity. Section capacity is defined as the “Number of train which can be run on the section in 24 hours”. This could be expressed in three different ways:
a. Maximum line capacity
b. Practical line capacity
c. Economic line capacity
a. Maximum line capacity: this is represented by the maximum number of trains that can be entered in the master chart so that it is impossible to introduce even a single more train on the section concerned.
b. Practical line capacity: the practical line capacity is represented by the practical number of trains per day which is obtained from the above mentioned maximum line capacity making allowance for such factors as time required for maintenance of permanent way, time margin for scheduling and other operational irregularities. In actual practice the train scheduling is based upon this capacity. When we speak of line capacity in general, we mean practical line capacity also known as effective line capacity.
c. Economic line capacity: When line capacity is under utilized, increase in train services follow the pattern of law of increasing returns due to more intensive utilization of fixed assets. However, as the number of trains to be operated on a section grows larger and larger and the section starts getting saturated, it becomes more and more difficult to increase the train services without increasing the time loss in train operation.
As a result, the utilization efficiency of the rolling stock and the train crew decreases and maintenance cost of the track increases. This leads to gradual increase of the transportation cost per train kilometer. The optimum number of trains which can be run on the section economically is the economic line capacity.
Calculation of section capacity: Though various formulae are there, CR follows the Scott’s formula which is as under:
Where C = Line capacity
T = Running time of the slowest train over critical block section
t = Time for block operation
e = Efficiency factor
Measures with incurring expenditure:
1. To reduce the block section
2. To improve the speed of trains
3. To provide the automatic signals
4. To provide extra corridor
5. Increase use of modern signaling system
6. Provision of Train describer
7. CTC on double line
8. Improving speed of goods train
9. Use of EMU and DMU for stopping train
10. Provision of AWS
11. Provision of ACD
12. Provision of PI / RRI / Electronic interlocking / SSI
13. By increasing CSL / CSR of all the running lines at all stations and yards.
Measures without incurring expenditure
1. Proper planning
2. Proper controlling
3. Proper efficiency
4. Time tabling
5. Proper maintenance of instruments
6. To reduce the time in block operation
7. To reduce the crossing and precedence
8. By implementing Management information system
9. By introducing new software through development of IT
10. By using new techniques in the infrastructure
11. By not using separate traction for different sections
12. To run heavy-haul goods trains
Order of priority for increasing line capacity works:
As section capacity works involve huge investments and long gestation periods, planning for such works has to be done with meticulous care to avoid traffic bottlenecks on one hand and uncalled for expenditure on the other hand. So it is necessary to follow the sequence below for considering increase in section capacity
(a) Organizational and operating measures to ensure optimum utilization of the existing operating assets as follows:
i. Time table improvements.
ii. Reducing disparity in inter-sectional running times.
iii. Review of sectional running times.
iv. Improving efficiency of staff.
v. Efficient operation of yards, station and terminals.
vi. Improved maintenance of equipment.
vii. Monitoring of trains by Officers and Inspectors.
(b) Technical measures:
i. Signaling and Interlocking improvements.
ii. Motive power improvements
iii. Civil Engineering improvements will include following:
(a) Opening additional crossing stations.
(b) Strengthening the permanent way and bridges.
(c) Improvements in alignment, eliminating surface road crossing, removing speed restrictions, providing 1 in 16 turnouts to permit higher speeds on loop lines.
(d) Easing of gradients.
(e) Patch doubling (Doubling of a section is not undertaken in one stage but in phases, the Work being called phase doubling or patch doubling)
(f) Doubling / Triple line / Quadruple line.
The Throughput of a section is the total quantum of Traffic which can be transported over the section in a period of 24 hours.
The traffic moved includes Passenger Traffic and Freight also. The Passenger Throughput is calculated basing on the number of passengers traveled and the distance they traveled. Passenger Throughput is calculated in terms of Passenger Kilometer (PKM)
Passenger Throughput = No. of Passengers Traveled X Distance they traveled in Kms
The Goods Throughput may be expressed in terms of:
(a) Number of wagons moved or
(b) Gross Tonne Kilometers or
(c) Net Tonne Kilometers carried over a section.
Generally, ‘Throughput’ in Railways refers to Goods Throughput for day to day Operation & is expressed in terms of number of wagons. But for Commercial Transactions it is expressed in terms of ‘Net Tonne Kilometers’. Because NTKM indicates the ultimate productive work done by Railways, a keen observation and effort required to improve NTKM.
Advantages of higher throughput:
(1) Wagon Utilisation Increases
(2) Increase in Railways Revenue.
(3) Yard / Sectional Congestions Eased.
(4) Reliability Increases.
(5) Customer is satisfied and repose confidence on Railways.
(6) Cost of Transport of Freight Reduces.
(7) Interchange commitments with adjoining railways fulfilled
Steps to improve throughput:
(A) Running more number of Trains:
a) Utilise the Section Capacity fully by running trains with CC loads
b) Discourage Light Engine Movements by ensuring that every engine carries sufficient Load.
c) Adopt vigorous marketing strategies
d) Timely ordering of trains.
e) Keeping targets periodically and monitoring.
f) Offer of incentives to efficient staff (Running Crack Specials, Special Trains)
g) Switching over traction from diesel to AC.
h) To utilize more HP locos to run trains with high speed.
(B) Increasing load per Train:
a) Increasing loop capacities.
b) Provision of High Capacity Wagons.
c) Improvement in Track.
d) Multiple Loco Operation or Providing more powerful locomotives.
e) High capacity bearing track shall be used
f) To reduce tare-weight
g) Using technology
h) Platform low level bogie containers
In order to improve the throughput, apart from measures taken for augmentation of line capacity, trailing load has to be increased to improve throughput by
a) Inducting High Capacity Diesel and Electrical Locomotives and Multiple Operations of Locomotives.
b) Improved Rolling Stock with CBC coupling and draw bar capacity of 80 tones or more.
c) Improved roller bearing on Rolling stock
d) Increasing carrying capacity of rolling stock without much increase in length or tare weight.
e) Improved Braking System (Air Brake and Disc Brake System) to maintain desirable ‘Braking Distance’.
f) Increasing Permissible Axle Load and permissible moving dimensions by Civil Engineering Works.
g) Increasing Loop Capacity and Strengthening the Loop Lines.
h) Improved system of Communication between Engine crew, Train Staff, Station Master and Controller.
i) Adequate Terminal Capacity and facility to deal with Heavy Haul Operations.
j) Re-scheduling and Curtailing running of slow stopping passenger trains on heavy haul routes or on dedicated tracks.
k) Integrated ‘Mega Blocks’ to prevent frequent departmental maintenance block.
l) Up gradation and modernization of techniques and methods of attending to trouble shooting and break downs.
m) Up gradation in the Skill and Knowledge of ‘Train Running’ and ‘Train Passing’ staff.