When a hazard alert, such as a construction zone or a stopped vehicle is posted, it should not simply expire. It should remain active until a user explicitly responds that it's "Not there."

There's no reason that a long-term construction project, for example, should have to be reported repeatedly day after day for months. The same applies to most types of alerts, such as broken traffic lights and potholes. Once the hazard is gone, users will say so. Until then, it should remain active.