"Put the brakes on and the bus just slides," he said, adding that the root of the problem was a lack of watertable maintenance.
"No one's cleaning out the drains, so the water runs across the road, scouring out channels and breaking the road edge," he said.
"Some places are just about impassable, and it's going to get worse given that we are bound to get more wet weather for some months."
A slip on Whangape Rd had deteriorated over recent days, thanks to heavy rain, Mr Swinburne added. It had been marked with pegs but nothing had been done about repairing it, and it was now close to closing the road to school buses, if not all traffic.