Hollow molded plastic support member for use in forming a variety of traffic warning devices has an inverted Y-shape which forms a pair of spaced angled legs and a vertical post portion. The post portion includes a pair of vertically elongated, spaced apertures defined by integral plastic connecting walls which space the opposed planar side portions of the support member from each other. An opening in the post portion permits ballast to be loaded into the hollow interior of the legs. A single support member can be used in combination with a vertical member having portions which snap fit with the apertures to form a three-legged sign or light support. Pairs of support members can be used with a variety of disclosed cross bar arrangements to form barricades and warning signs. The snapfit design of several of the disclosed warning devices permits the devices to come apart when hit by a vehicle without causing damage to either the vehicle or the warning device.