Top Layer:

Top layer has two basic functions. Firstly provide waterproofing for road and secondly provide adequately smooth surface for the least surface friction. Usually, PCC/RCC roads do not require this layer.
Bituminous road material is available to make smooth surface like glass. This material works as waterproofing also. Due to vibration PCC/RCC road does develop hair cracks and need waterproofing. Material used for this layer is the costliest. Top layer must have adequate slope and should not accumulate water. If proper slope is not maintained in lower levels thickness of this layer increases leading to high cost. This layer does not provide any strength to the road. This is also liable to develop cracks if lower layers are not constructed properly. Once cracks are developed the road gets easily damaged on account of water sipping through these cracks. Premix bituminous carpet is neither a solution for new road nor for road repairs. Many times every year new layer of bituminous carpet is laid on existing layer. This is not a solution for good road. On the other hand road level may rise above plinth level of buildings and the buildings may get waterlogged. Most of the local government bodies adopt premix carpet as solution for road repairs. This practice is against engineering norms.