When can vehicle 1 move forward?

Vehicle 1 can move forward before vehicle 2 because it is likely positioned in a way that allows it to proceed without obstructing vehicle 2. In many driving scenarios, when approaching an intersection or when there's a line of vehicles, traffic rules dictate that vehicles can advance or make turns only when their path is clear and when it's safe to do so.

The traffic flow often prioritizes certain movements; for instance, if vehicle 2 is stopped, vehicle 1 has the opportunity to move ahead, assuming there are no other restrictions or signals preventing it. This allows for more efficient use of road space and helps to maintain the flow of traffic.

The incorrect options suggest conditions that could either conflict with safe driving practices or do not accurately represent the legal or practical circumstances surrounding vehicle movements in traffic.