AbstractThe use of cul-de-sacs and one-way streets has been proposed as a means to reduce crime in several locales. Closing streets or restricting flow patterns on them make travel through neighbourhoods more difficult and may also serve to define better the neighbourhood. Both of these effects it is hoped will reduce crime. A deleterious side-effect of cul-de-sacs is the increased difficulty of travel for all people who traverse the neighbourhood—specifically providers of essential services such as the fire department and the police department. A problem faced by city planners is where to most effectively place these impediments to travel so that they make travel difficult for the criminal, but not too difficult for residents and allow essential services to be provided expeditiously. This problem is modelled and its complexity explored, with several simplified variants studied. A prototype interactive design aid, that will enable city planners to use a computer to develop solutions, is described and its potential use is explored.