He instantly thought a "flash of light" that caught his eye was a speed camera and barely had time to think, 'they'll get that truck for going too fast', when wham, something was hurtling toward his head.
"But of course there was no speed camera. The flash is likely to have been the glint of metal as it came flying up off the surface or off a truck," he said.
He thinks it may have been a bolt, spring or some other metal fitting as the small, deep crater where it bounced on his bonnet is hard edged, unlike the dent a rock might make.
Mr Allen was doing about 30km/h but aware some other drivers were not even slowing to the signposted speed limit of 50; that limit still too high for the conditions, he thinks.
He contacted the Advocate about his near miss after reading about a pothole on a bridge approach on SH1 near Baldrock Rd, Brynderwyn, that caused at least 30 punctures on Thursday.
That fairly deep and 80cm wide pothole was hidden by surface water in heavy rain.
New Zealand Transport Agency (NZTA) Northland highway manager Brett Gliddon said potholes are not unusual at this time of year due to wet conditions and there were extra repair crews on board.
He said motorists were encouraged to report potholes and other hazards to NZTA at 0800 4 HIGHWAYS .