A spacer for a road safety barrier is provided. The spacer includes a rail support having a front face to be fastened to a rail, a rear face to be fastened to a post and a flange that connects the front face to the rear face. The front face includes a connector housing and a weaker area connecting the connector housing to the upper edge of the front face, the mechanical resistance of the weaker area being strictly lower than the intrinsic mechanical resistance of the constituent material of the remaining part of the front face of the rail support. The spacer also includes a rail guide including a fastening area for fastening the rail guide to a post above the rail support, a connecting piece and a rail reinforcement area for fastening the rail guide to the reverse side of the rail.