Where the presence of a truck that is about to enter the road is automatically detected, the TC-31A sign may be used, with two amber flashers, one on each side of the sign, alternating in a 'side to side' manner, activated by the detector, so that the amber flashers provide a positive signal to motorists that a truck is about to enter the road. When the TC-31A sign is used, the TC-20AT when flashing tab sign must also be used.