Which of the following is NOT a type of guardrail end?

The correct choice is based on the identification of guardrail end types typically used in safety applications for roadways. Sand-filled, shielded, and foam-filled guardrail ends are common forms of systems designed to absorb impacts and reduce the severity of collisions.

Sand-filled guardrails utilize a container filled with sand to help dissipate energy upon impact, while foam-filled options incorporate materials that compress and absorb force. Shielded guardrail ends often involve protective elements that redirect or cushion the impact so that a vehicle doesn't collide directly with the rail itself.

Concrete, on the other hand, is not typically classified as a guardrail end type, as it does not serve the same purpose as the others listed. Instead, concrete barriers are standalone protective measures that do not function as part of a guardrail system. They are used for different applications, such as separating traffic lanes or preventing vehicles from crossing into hazardous areas, rather than ending a guardrail run.