Gardaí yesterday warned motorists in Co Kerry to watch out for punctures after thousands of nails were spilled from what is believed to be a truck or builder's van.
The main road between Kenmare and Kilgarvan was closed while gardaí attended the scene, and council workers cleaned up the one-inch (2.5cm) nails.
The nails were first spotted shortly after 9am at Clontoo.
Ann Randles was one of the first to alert gardaí. During a school run, she noticed what she thought were pellets on the road. She soon heard "a hissing" sound and two new tyres on her car were punctured. Some 20 nails were in one tyre.
Dozens of motorists are likely to have been affected as the incident happened at one of the busiest times of the morning, according to Garda Paul Brown.
Some motorists reported all four tyres punctured.
Garda Brown said the nails may have been carried on tyres for some miles, and then deposited on the N22 between Cork and Killarney where other motorists could be punctured.
The nails were of a slab-type design used in electric guns and are normally packed in 20kg boxes.
Motorists in the area can expect flat tyres possibly for the next week as a result of slow punctures.
Gardaí are investigating the incident.