Which safety measure is advisable when working under an unstable vehicle?

When working under an unstable vehicle, implementing a tension buttress system is a crucial safety measure. This practice involves the use of supports that help stabilize the vehicle and prevent it from moving or collapsing while personnel are underneath. By effectively distributing the weight and providing additional support, a tension buttress system significantly reduces the risk of injury.

Lifting bags also serve a purpose when stabilizing vehicles, but they are typically used to lift rather than provide ongoing horizontal stability. Wearing safety harnesses is important in many contexts but doesn’t address the primary concern of securing a vehicle. Removing the wheels can compromise the vehicle's stability and is generally not advisable because it can lead to unforeseen risks.