|(a) A barrier required under §21.706 of this subchapter must be determined by the department to be sufficient to prevent the normal passage of vehicular traffic from entering the site of the pit. (b) The design of the barrier must be approved by the department to insure proper performance. (c) The barrier may be a guardrail, concrete barrier, or berm barrier. A guardrail must meet the current department specification and standard detail for metal beam guard fence. A concrete barrier must meet the current department specifications and standards for a rigid barrier and the appropriate standards for end treatments, attenuators, and crash cushion. A berm barrier must meet the current department specifications and standards for berm barriers. (d) A barrier that was determined to conform to construction standards for the issuance of a safety certificate and that has deteriorated so that it no longer meets the construction standards applicable at the time the safety certificate was issued will be required to be improved to conform to those standards.