an arrangement in concrete blocks which are intended to be positioned end - to - end to form barriers for e . g . roadways and parking lots . the concrete blocks have an elongate shape with an essentially triangular cross - sectional configuration with rounded side walls , and are interconnected by means of t - shaped metal pieces , the latter being secured in the end faces of the blocks during the casting thereof and formed with cross - bars , the interconnection of the blocks being effected in that two such cross - bars at adjoining end faces of two concrete blocks positioned end - to - end are enclosed by a tubular member , whereby the blocks are locked together . the blocks may be provided with a device widening their upper part and increasing the ability of the block to guide vehicles safely back to the roadway .