The Motor Industry Staff Association Misa on Friday warned motorists to remain vigilant against criminals on the N4.
The latest case occurred eastbound between Silverlakes and Donkerhoek when rocks were placed on the road, causing several vehicles to suffer flat tyres, the union said.
Five weeks ago, one of Misas employees was involved in a spiking incident on a on-ramp of the N14 in Krugersdorp when objects were placed in the road. She managed to escape unharmed.
