Friday, November 30, 2012

Why certain zones are prone to railway accidents?

A paper published this year in Physica A, a reputed international journal, has in a very scientific way identified the reasons behind the 11 railway accidents involving express trains in 2010 . Aside from clearly establishing the well-known cause — the disproportionate increase in railway traffic compared with infrastructure — it has also identified zones that are insufficient to handle the congestion and reasons for this.

The authors have identified two main reasons for the 2010 accidents. First, railway traffic has grown disproportionately to railway infrastructure, particularly railroads and routes. Second, there are serious flaws in the scheduling of trains on some routes. So much so that the Railway system would not be able to handle the traffic on certain routes if all trains were to run as per schedule. Hence, the Railways resort to making trains wait at signals, leading to long delays in trains’ run-time. This is alarming, as the system intentionally introduces the possibility of human error and/or system failure leading to accidents.

The 11 accidents were due to derailments or collisions between express trains or some sort of failure of the railway system itself. Incidentally, eight of the 11 accidents took place in a zone which they call the Indo Gangetic Plain (IGP) — a north-eastern belt. This is no coincidence, as the statistical analysis by the authors clearly identifies the reason.

They find that the Indo-Gangetic Plain hosts some of the most traffic-intensive segments of rail routes — seven out of the 20 that they consider high-traffic. Comparing data gathered from 1992 to 2010 from “trains at a glance,” they conclude that this is because the infrastructure such as railway lines and tracks have not grown over the years, whereas the number of trains has increased manifold. They identify the most risk-prone ‘trunk segment’ as the Delhi-Tundla-Kanpur one and identify the Vishakhapatnam-Vijayawada trunk segment from the southern zone as the “safe standard” based on the empirical evidence that it has not had any accident so far.

How sound is the rationale behind keeping the south zone route as a safe standard? Is it not better to keep an absolute value on safety? In an email to The Hindu, Niloy Ganguly noted: “It will definitely be better to use an absolute standard, but we do not know of any such standard for IR….

Note that there have been derailments/collisions even in South India in 2012. Hence, some segments in South India also seem to be nearing the risky zone. This means that the condition of IGP is even worse than what we had estimated in our paper (since the safe standard itself is no longer very safe).”

Another parameter is the headway, or time lapse between two trains as they cross the same point. The possibility of two trains coming dangerously close to one another increases as the headway reduces. They found two segments clearly coming out as risk-prone segments — the Delhi-Kanpur segment and the Ahmedabad-Surat segment. The Vishakhapatnam-Vijayawada segment has a much higher headway and is therefore safer, relatively speaking. Of the two lower headway segments, the Ahmedabad-Surat segment has trains with low headway running throughout the day, whereas in the case of the Delhi-Kanpur segment, trains get bunched up in the early hours.

Runtime delays of trains on these segments were also studied. While 20 per cent of the trains on the Delhi-Kanpur segment were delayed by more than one hour, only about three per cent of the trains on the Vishakhapatnam-Vijayawada segment were delayed to that extent. The delays reflect the high degree of congestion and frequent waiting of trains at the signals, and hence a possibility of an accident.

They also analysed traffic congestion at a fine-grained level by undertaking a simulation of the traffic flow according to the IR schedule. The authors modelled the “block system” followed by Indian railways.

A railway track is divided into block sections (of about 4-8 km) such that when one train is occupying a block, no other train is allowed to enter that block on the same track. Signals or stations at the end of the block control the traffic.

From the simulation, it became apparent that there would be more than two or three trains in one block quite frequently in the Indo-Gangetic Plain if all trains were to run as per schedule and not stopped by signals.

Now, while some blocks have three tracks, most of the IR blocks have only two tracks and so can accommodate at most two trains. So this indicates that the infrastructure is not sufficient to handle the traffic and this is only being managed by stopping trains and delaying them beyond the scheduled time.

Source: The HINDU

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