Indian Railways has launched an extensive programme to convert the metre and narrow gauges to broad gauges. Moreover, steam engines have been replaced by diesel and electric engines. This step has increased the speed, as well as, the haulage capacity. The replacement of steam engines run by coal has also improved the environment of the stations. Metro rail has revolutionalised the urban transport system in India. The replacement of diesel buses with CNG-run vehicles along with the introduction of the metro is a welcome step towards controlling air pollution in urban centres.

Assertion: The speed, as well as, the haulage capacity of Indian Railways has increased in the past few decades.
Reasoning: Steam engines have been replaced by diesel and electric engines.

Both Assertion (A) and reasoning (R) are correct, and R is the correct explanation of A.

Moreover,  steam engines have been replaced by diesel and electric engines. This step has increased the speed, as well as, the haulage capacity. The replacement of steam engines run by coal has also improved the environment of the stations.