Local knowledge is clearly an advantage in street photography. However when intending to explore an unknown urban area it is worth doing some research before setting out. This is not particularly difficult in the internet age because tools such as Google Earth, Google Street View and numerous urban exploration websites are available.
It is certainly worth exploring an area of interest on foot a day or two before doing any photography. Carry a small notepad or audio recorder and make notes about the areas visited. Some will be more suitable than others, so there will be no need to carry equipment to unpromising areas. It is also worth taking a small compact camera to collect snaps of sites of potential interest.
Urban exploration websites have vast quantities of information, including photographs, relating to derelict and unused sites of all descriptions. However, urban exploration is very different to street photography. In some cases urban exploration photographers were obviously trespassing and may have put themselves at risk in gaining access. In most cases there are no people in the images.
Every photographer must decide for themselves what level of risk is acceptable, but there is no need to trespass or climb over fences to obtain good street images. Sites that are fenced or closed are, by definition, more or less deserted and unlikely to provide opportunities to photograph people and their interactions with the environment. If there is good reason to be interested in gaining access to a private or restricted site, try asking for permission to take photographs. At least in some cases, access may be allowed and the need to take risks is removed. The best street photographs are obtainable on the public side of fences and restrictions.