Indian Railways has taken a major step in increasing their freight-carrying capacity. They have decided to permit additional loading of wagons above the prescribed axle load limit of 20.3 tonnes per wagon, a norm that was fixed more than four decades ago.

This was done on a trial basis to see what benefits accrued. The results are already apparent. The railways will carry 64 million tonnes extra freight during the current year. 

Such an impressive increase in the freight-carrying capacity would not have been possible without increasing the loading limit of each wagon. However, doubts have been raised about safety norms being compromised because of the additional pressure on the tracks.

But these doubts are misplaced because this is not the first time that this is being done. Higher loading was first practised in the early 1980s when M S Gujral was the chairman of the Railway Board.

He turned around the system by several innovative measures, one of which was to increase the loading capacity of each wagon. This policy was subsequently abandoned on the ground that higher loading would damage the tracks. But was the judgement correct?

The argument that by increasing the loading limit by 8 tonnes, a wagon would adversely affect safety needs to be considered in a historical context. Until the 1960s, steam locomotives were in use and many of these locomotives had axle loads varying between 22.5 tonnes and 23 tonnes.

In steam locomotives, a phenomenon called "hammer blow" occurs during every rotation of the wheel, which tends to increase the impact loading on the track by 25-30 per cent. In the era of the steam locomotive, the track structure consisted of 90-pound (or 45-kg) rails, wooden sleepers and fish-plated rail joints.

The Indian Railways now uses electric and diesel locomotives that have no hammer blow. Moreover, the old 45-kg rails have been replaced by superior 60-kg rails that are placed on concrete (instead of wooden) sleepers.

Rail sections are now welded for long lengths at joints, thereby reducing the severity of impact in comparison to fish-plated joints. The welded tracks of improved strength under reduced impact loading today are, therefore, more than a match for the tracks used in the past that used to withstand an axle load of 23 tonnes with 30 per cent additional impact loading.

The other apprehension is the adequacy of the strength of bridges, most of which were constructed many years - if not decades - ago. These bridges had been designed for steam locomotives with higher impact loading.

The design factors were intentionally kept on the high side to make these bridges extra safe, especially since stress measurement techniques available at that time could not accurately indicate stress levels encountered under different operating conditions.

It can, thus, be safely argued that existing bridges can take higher loads than what is conventionally presumed or generally believed.

Modern techniques can assess bridge capability fairly accurately and in good time. It is widely acknowledged that structures do not collapse immediately under conditions of overload but only when fatigue sets in after extended periods of increased stress. Thus, there is reasonable time to have bridge capability assessed while increasing axle load.

Another issue pertains to the legal aspects of increasing the axle load. The current 8 tonnes a wagon increase in the axle load is on a trial basis. After an initial period of reluctance, the ministry of railways is at present processing the clearance of the increased axle load with the Commissioner of Railway Safety.

The current increase in the axle load by 8 tonnes a wagon is well within the prescribed safety margins and, therefore, there is no need to ring alarm bells.

A basic constraint being faced by the Indian Railways is poor loadability of wagons, which, in turn, reduces freight capacity since the payload carried per train is less than what most international railway systems currently manage to achieve.

This makes it necessary for more trains to be run for carrying the same freight output, which is not possible unless network capacity is expanded by undertaking substantial capital investments.

The two primary factors that limit the loadability of wagons are Maximum Axle Load and Maximum Moving Dimension. The axle load generally permitted on the Indian Railways is 20.3 tonnes. Each wagon normally has four axles. This translates into each wagon being limited to a gross load of about 81 tonnes.

Since the average weight of an empty wagon or "tare" is around 25 tonnes, the payload carrying capacity of the wagon is just 56 tonnes. A margin of two tonnes is permitted to cover loading inaccuracies.

Thus, the payload is a maximum of 58 tonnes with a tare of 25 tonnes, giving the rolling stock of the Indian Railways a payload to tare ratio of 2.32 as compared to a ratio of between 3.5 and 4 on most railway networks the world over.

An axle load of 25 tonnes has become an international norm in freight intensive railway systems in most countries. If the Indian Railways had a 25-tonne axle load system, the gross weight of each wagon would be 100 tonnes, implying an increase of 19 tonnes over the present gross weight of 81 tonnes.

Since the entire quantum of increase would be in terms of payload, the total payload would increase from 58 tonnes at present to 77 tonnes or an increase of nearly one-third - to be precise 32.8 per cent - a major increase in the carrying capacity of the Indian Railways by merely increasing the axle load.

The second primary factor limiting loadability is the maximum moving dimension (MMD), that is, the cross-sectional space envelope that limits the width and height of wagons on tracks.

All clearances in the route of bridges, foot overbridges, platforms, signal posts and so on, are based on the MMD. In other words, there is no scope for any significant increase in the width and height of the wagons on the Indian Railways.

The time is opportune for the Indian Railways and regulatory bodies to get out of its time warp and start following loading norms that are prevalent the world over. There is a welcome change in the mindset but the process has to be sustained.

It is also necessary to start building wagons with wheels of smaller diameter and with increased width and height within the existing maximum moving dimensions to increase wagon-loading capacities.

The author is Senior Fellow at the Asian Institute of Transport Development.