Dogs sometimes have not had enough socialization and have missed out on learning what people, buses, trains, other puppies and dogs and a host of normal day to day things are. If they miss out on this stage, then they can become fearful of their environment. This means they become frightened and can start barking at cars, people or any moving objects. For those dogs nervous of new environments, it is critical to start small and slowly desensitize. Adult dogs can be desensitized but it takes time. Make sure you are patient and don’t rush it.