We propose the following method for evaluating road network patterns. An evaluation of these patterns is important not only for an understanding of the structure of a city, but also for compliance with the rule in the Building Standards Law (the basic law related to buildings and cities in Japan), that makes it possible to preserve lanes (i.e., narrow roads less than four meters wide). This rule, however, does not provide a method for judging whether or not road network patterns are laid out in a suitable manner. We conducted an interview at a local administrative office and found that this provision is closely related to the need to ensure access for fire-fighting equipment and personnel. Thus, by determining whether, in an area encircled by wide roads, there is a 'fire-inextinguishable area' (FIA) more than 140 meters from the nearest wide roads (i.e., an area where fires cannot be put out effectively), we can determine whether or not road networks are appropriately laid out. In addition, we present a mathematical formula showing that if there is no 'fire-inextinguishable area' (FIA) in an encircled area, there will not be an unsuitable, blocked position for putting out fires. Observing this difference, as well as the ease in turning right or left at intersections in the areas encircled by wide roads, we found that grid road network patterns are appropriately set up. Also, by using indices based on graph theory as a complementary method for evaluating road network patterns, we found that while almost all narrow road networks are classified as belonging to the tree pattern, some of these narrow networks are considered to be almost in the grid pattern, and are directly connected to wide roads. This indicates that actual road networks in Tokyo have weak connectivity, which may cause difficulties in ensuring two-way escape.