breakable when impacted by a car and prevent build up of debris under the front of the car thus avoiding ramping debris can be a potential problem because of the low cg of race cars and their minimal ground clearance also the fragmented parts can be quickly cleaned up because of the tapers on the walls of the tubs and rings for each size barrier a plurality of tubs can be nested together and a plurality of rings can be nested together to facilitate shipping and storage of the two components also the tapers on the tub and the ring facilitate their removal from the molds in which they are produced further even though the plastic tubs and rings are of thin wall construction they are sufficiently strong to resist breakage during normal handling and installation barrier 20 and similarly barriers 20a and 20b is assembled and installed by placing flange 24 of ring 22 on level ground placing tub 34 on ring 22 with upper edge 30 nesting within notch 44 and then filling the tub with the dispersible mass such as water or sand the flared flange 24 distributes the weight of barrier 20 over the ground and prevents the ring 22 from sinking into soft surfaces notch 44 cooperates with upper edge 30 of ring 22 to hold tub 34 and mass 36 in place on ring 22 fig5 and 6 illustrate another embodiment of the invention the frangible barrier 50 includes an outer thin plastic casing 52 attached to an inner thin plastic casing 54 forming an inflatable air chamber 56 there between casing 54 has a bottom wall 58 and a generally spherical sidewall 60 defining an open pocket 62.