The reason for northern states depending on more on Railways is the length of rail line and roadways is the same between Delhi to respective state cities like Jaipur Ajmer, Chandigarh Ludhiana Amritsar,n Agra Kanpur Lucknow Allahabad. While in southern India the distance between metro cities or towns to state capitals are shorter by 50-100 km in some routes making road transport a better alternative for some residential and business parts of the 3 metros.
Second the truck traffic is very high in northern states that road network takes more time for personal vehicle as well as high end buses as in connecting southern metros. In southern states to metros it's easy to achieve an avg of 60-70kmph during night...
more... while in northern states its 50-60kmph.