why dig up roads

we dig up roads even before the tar dries up.
for valid reasons many times. to lay cables along side.
but for gods sake why not lay an iron or concrete pipe
along all new roads . cables and even water pipes can
easily be pushed thru this conduits. with out digging
up the roads. these pipes can be even even across the
road at junctions for future use. but then if roads cannot
be dug up what   p w d   for . what prestige water works
departments can claim.