. Because precise portioning of the various the various attenuator components of crash barriers to be fastened is an absolute necessity, alignment of the parts with their mounting holes in the concrete is critical. This exact position requirement makes it virtually impossible to cast anchors in place and difficult to align some types of drop-in anchors. This, however, is no longer a problem. Installation times for auto crash barriers can be reduced by using parabolic anchor bolts Installation of the type drop-in fasteners calls for relatively few steps. The anchors require a drilled hole no larger than the bolt diameter itself, so the holes can be drilled while the attenuator parts are in place. Since the hole diameter is no larger than the bolt, less concrete need be removed.