Indian Railways: WAP4 vs WAP7, Which Locomotive is Better?

• Report rights infringement
• published: 02 Feb 2013
• views: 130788

One of the most stirring debates in Indian Railways for the past decade is based on the performance of the WAP4 class of locomotives in comparison to the newer three-phase WAP5 and WAP7 locomotives. Voices in support of three-phase locomotives point to their faster acceleration capabilities courtesy the higher horsepower ratings - 6,000 HP and 6,350 HP for WAP5s and WAP7s, compared to 5,350 HP for WAP4s. Proponents of WAP4s point out that despite the advent of WAP5s and WAP7s as regular locomotive links for a multitude of trains, including Rajdhanis, Shatabdis, travel times for these trains have not significantly reduced. Through two videos documenting a natural experiment, I have attempted to observe and contrast the acceleration of a WAP7 and WAP4 in real-life and discern any significant difference between them. The key feature of natural experiments is that all other factors which might affect the variable of interest, in this case, acceleration capability, are held constant. In this light, this compilation presents the acceleration of the Howrah Rajdhani Express, powered by a Ghaziabad WAP7, and the Poorva Express, powered by a Mughal Sarai WAP4, upon departure from the station of Parasnath, Jharkhand. Both videos capture approximately the first five kilometres covered by both trains after exiting Parasnath. Parasnath is a small station and the trains halt on the platform on the main line and thereby, there are no barriers to acceleration like a number of points or switching of tracks. In the absence of any additional speed restrictions imposed by railway authorities, trains have the license to accelerate to their maximum permissible speeds (MPS) at their earliest upon departure from the station. Both the Rajdhani and the Poorva have no halt after Parasnath till Dhanbad so we would expect them to have a comparable performance in terms of acceleration. In this respect, if we assume away certain differences (listed below), this is as close to a natural experiment as we in our roles can passengers can enact. An improvement on this would probably involve the racing of two identical trains side-by-side on the same day with the two different locomotives. The differences which could affect the observed evidence in the video are: 1. The videos were captured within three months of each other. Thus, there could be some minor speed restrictions imposed on either trains, affecting their acceleration, though I do not believe that was the case, given how both trains took-off! 2. The Poorva Express is a 24 coach rake, as opposed to the 19 coach Rajdhani so there is a slightly heavier load for the WAP4 hauling the Poorva. 3. The Rajdhani is a fully air-conditioned rake whereas only 6 of the 24 coaches of the Poorva is air-conditioned. The drag effect on the Poorva is therefore much higher, which would reduce its acceleration capabilities. 4. The Rajdhani was over 3 hours and 20 minutes delayed so there was theoretically a higher incentive for the Rajdhani to accelerate quicker and make up some time. This and the above factors add a small bias against the Poorva and in favour of the Rajdhani. 5. I was in the first coach of the Rajdhani and the 18th coach in the Poorva. 6. There is a 20 second lag in the Rajdhani departing, from when I start videoing. For the Poorva, I started videographing around 20-30 seconds after the train departed. The results I must say surprised me (though pleasantly). The WAP4 displayed an absolutely stunning performance. There is pretty much no difference in performance of both these trains for the first two minutes (around 3 km) and there is a slight difference in favour of the Rajdhani after that. T The WAP4 hauled Poorva notches up to 80 kmph in about 2 minutes and 25 seconds, 100 kmph in around 3 minutes and 110 kmph in around 3 minutes and 30 seconds. The WAP7 powered Rajdhani on the other hand hits 120 kmph in 3 minutes and 10 seconds and 130 kmph in 3 minutes and 30 seconds. Towards the end of the video, we cross an abandoned block hut and the Poorva takes approximately 15 seconds more to get there, which can possibly be explained by the higher speeds attained by the Rajdhani for at least 20 seconds. However, we also need to bear in mind factors 2 and 3 -- the slightly higher load of the Poorva and the drag it faces due to a higher number of non-airconditioned coaches. Taking these factors into consideration, there is actually very little difference between the performances of two locomotives. Of course it is unscientific to make any strong conclusions on the basis of a single pair of observations but given the evidence of the two videos, we can at least commend both the WAP4 locomotive, and its loco-pilots, for a superb performance, where they almost matched a WAP7 hauled Rajdhani with a higher speed permit, blow for blow!