Q. Isn't electric traction better than diesel because ... ? Isn't diesel traction better than electric traction because ...?
The debate over the relative merits of diesel and electric traction and which one is 'better' is a lively one and springs up every now and then on IRFCA and other railway forums. There are advantages and disadvantages to both forms of traction, and each is suitable for certain applications. Economic and operational advantages of either type of traction may be different in the Indian context, and direct comparisons to European, American, or other railway practice may not be appropriate. *Some* (and only some!) of the considerations that frequently come up in this discussion are listed below. However, the main thing to note...
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about this topic is that it has caused much rancorous debate among railfans, without either side 'winning', and there may not be much benefit to raking up the debate again unless you feel that there is substantial new information or novel points to be considered in your argument.
Trade: Diesel uses oil that's imported with foreign exchange; electricity can be generated from plentiful domestic coal or hydroelectric plants, etc.
Pollution: Diesel yields nitrogen and sulphur oxides and particulate matter; electrics are cleaner locally but the power plants generate pollution or may be environmentally dangerous (hydroelectricity, etc.). Diesel technology is getting cleaner all the time. So is the pollution control at power plants, where efficiencies of scale help. Clean coal burning technologies may help further.
Efficiency: Diesel involves the whole petroleum transportation system and is limited by the efficiency of the internal combustion engine on the loco. Electrics are more efficient on-board (no need for an engine), and power plants can have better efficiencies by scale, but there are problems of transmission losses and other inefficiencies in the distribution of power.
Freight Capability: The placement of the overhead catenary for electric traction prevents the use of double-stacking of container traffic. However, it is to be noted that with new, low-height container wagons, double-stacking may still be possible on electrified lines in India.
Reach: Diesels can obviously travel anywhere; electrics are limited to electrified lines. On the other hand diesels need to refuel periodicall while electrics can keep going.
Capital investment: Electrification involves large up-front investment to set up the OHE and power supply and may not be economic for branch lines or other areas with low traffic. Heavy freight movement and busy passenger lines are the best suited for electric traction.
Power: Electrics can supply a lot of additional power for short periods since they can draw more current as needed from the OHE; diesels are limited in the power they can provide at any time.
Maintenance: Diesels are generally somewhat more complex to maintain since they have many more mechanical systems associated with the diesel engine itself.
Plant failures, etc.: OHE failure -- perhaps because of problems at a remote power plant -- strands all electric locos in a region. Theft of OHE cables also affects all electric traction in a section.
Perception: There is a common perception that electrics are 'more advanced' than diesels. In fact both electric and diesel technology have been around a long time and both have advanced a lot and are still being improved tremendously.