A road traffic barrier module comprises a hollow body adapted to receive ballast and adapted at either end to link with similar modules to form a barrier in which there is a pair of upper and lower horizontal bolts passing through mating ends of adjoining modules and there is also a pair of cables the ends of which are also secured by the bolts. In an alternative form adjoining modules are linked by vertical pins passing through mating ends of the adjoining modules and there is a pair of cables the ends of which are also secured by the pin. The modules are molded from a plastic material and the walls may also be clad with metal pressings to increase structural integrity and to protect against damage.