I Walked the way from the Thane railway station to Thane west during the early morning hours and i was struck by the way the raods are laid with concrete blocks for big junctions where the buses have to take steep turns, and just plain tar roads for straight roads and sometimes even concrete roads too. this it appeared to me to follow some logic. the concrete blocks are hard and can withstand the wear and tear of the erosion made with the bus tyres. while the concrete road is very resistant to the corrosive effect of running water too(If iam correct).another thing i observed was that these concrete block paved roads were laid only at places where there is a sloping angle to the road, this enables the rain water to run away and not stagnate and i found this arrangement to be a very clever piece of civil engineering.Because stagnant water is more corrosive than running water.