A Semaphore or Traffic Light (Semáforo) is a signal device that is located at intersections and other places to regulate traffic, and therefore, pedestrian traffic. This type of device is usually installed on streets.
This means the right answer to the question ¿Dónde vemos un semáforo? (Where do we see a traffic light?) is:
Vemos un semáforo en una calle.
(We see a traffic light in a street)
Not in a truck (el camion), the highway (la autopista) because usually cars move faster there, neither in a key (una llave).
