You stop your vehicle upon seeing an officer with one arm extended horizontally; you may resume driving when the officer...

When an officer has one or both arms extended horizontally, they require users approaching from any direction that intersects the direction indicated by the extended arm or arms to stop, regardless of their direction of travel, and this remains in force even if the officer lowers their arm or arms, as long as they do not change position or make another signal. Therefore, driving may be resumed when the officer indicates so with the corresponding signal, such as giving long whistle blasts or using their arm to indicate that we may proceed. The officer lowering their arms means nothing — no signal is being given — and therefore driving may not be resumed under any circumstances in that case.