Using Potential Path Trees to Map Sex Offender Access to Schools

Many states and municipalities prohibit registered sex offenders from residing near schools or other places where children gather. Such residence restrictions are employed in order to prevent sex crimes against children by reducing sex offender access to possible victims. Although numerous academic studies suggest that residence restrictions fail to reduce crime rates or are otherwise inappropriate, the potential effectiveness of these policies has not thoroughly been evaluated from a spatial accessibility perspective. This study explores the spatial accessibility of sex offenders to public schools in a city with enforced residence restrictions, St. Louis, Missouri. The goal of the analysis is to examine how accessible schools are to sex offenders with a history of crimes against children or minors. Unlike previous studies, however, accessibility is measured not only near the place of residence but also during expected routine activities that occur away from the home, such as at the work place or during commutes. To accomplish this, methods of time geography are used to measure cumulative sex offender accessibility to schools based on the home and work addresses of registered individuals. Specifically, potential path trees are used to estimate sex offender access to schools given estimated daily travel budgets. The results show that, while few registered offenders in the city live near schools, nearly all are expected to come in close proximity to them either near the work place or during the expected journey to work. In the context of public policy, this suggests that—from a strictly spatial perspective—residence restriction laws are unlikely to achieve their goal of limiting sex offender access to school children