Guide dogs

Guide dogs, are normal dogs that have been trained to guide blind people. Usually are 'Golden retrivers' who lead this kind of people to across the street, among other things.
For the visually impaired control the dog should be able to realize potential dangers for the owner because  architectural barriers, requiring very high capacity as intelligence and advanced training level of the animal.

Although dogs can be trained to avoid various obstacles, do not distinguish colors like green and red so you can not interpret a stoplight.