Capacity augmentation has always lagged the traffic growth in IR since independence. So, there has been no appreciable increase in the avg. apeed of trains in spite of the fact that the operating speed of trains has increased due to strengthening/modernisation of track.
At the time of independence, most of the lines were single but sufficient for the traffic at that time. As the traffic increased very fast with rapid industrialisation & development, the tracks begin to get congested. Accordingly, the required doubling was not done or done too slowly. By the time doubling was done, the traffic is too high and demand third track!