One way gates are sometimes used to allow large mammals that are stuck inside the fenced road corridor to escape to the safe side of the fence. The metal bars are spring loaded, so they will close automatically after the animal has pushed itself through. Currently wildlife jump-outs or escape ramps seem to be recommended instead by road ecologists. One-way gates can injure the animals, especially if the metal pints are not protected with plastic knobs (much like tennis balls). One-way gates can also become two way gates if elk decide to bend the metal bars.