Distinguishing between a truck and two motorcycles based solely on seeing two lights at night can be challenging, as the visibility and characteristics of the lights can vary. However, there are a few factors you can consider to help make an educated guess:
Headlight Configuration: Motorcycles typically have a single headlight, whereas trucks generally have multiple headlights. If you can observe the number of lights on each vehicle, it may give you a clue. However, it's important to note that some motorcycles, particularly larger touring or adventure bikes, may have multiple headlights as well.
Spacing: Motorcycles generally have their headlights mounted closer together compared to trucks, which typically have headlights mounted wider apart. If you can perceive the distance between the lights, it might provide an indication of whether it's a motorcycle or a truck.
Height and Size: Trucks are larger and taller than motorcycles, so if you can judge the height and size of the lights in relation to the bridge or other objects nearby, it may help you differentiate between the two.
Sound: The engine and exhaust noise of a truck are usually louder and distinct from that of a motorcycle. If you can hear the sound accompanying the lights, it can assist you in identifying the type of vehicle.
Remember that these are general guidelines and not foolproof indicators. Other factors, such as the specific make and model of the vehicles, the presence of additional lights or indicators, and the distance between the lights, can affect your ability to accurately determine the type of vehicle you are observing. It's always best to exercise caution, maintain an appropriate speed, and yield to oncoming traffic until you can clearly identify the vehicles and ensure a safe crossing.