Urban areas continue to be at the forefront of new energy choices for transportation that improve environmental quality and resilience in the face of extreme conditions. A key challenge, however, is incorporating urban edges into the core so they also benefit from environmentally sound transportation that is also resilient to extreme events. According to U.S. census data, in the first decade of the 21^st century the least populated areas showed the highest rates of growth and according to NOAA, many of these areas also experienced record damages from disasters given their location and the lack of availability of resources to withstand these pressures. Public transportation is critical to surviving such disasters if positioned and protected adequately. Coverage of public transportation in outlying areas, however, tends to be uneven and equity issues arise which reduce availability and access even more for certain sectors of the population. This paper uses the lens of public transportation network characteristics to understand how viable services for outlying areas within cities are relative to dense inner areas and how efficiently smaller outlying areas are linked to urban cores so they can withstand adverse environmental conditions. Measures of connectivity, concentration and flexibility of services and facilities are identified and developed based on network science. In order to compare how different networks fare under adverse environmental conditions, the measures are applied to representative public transportation system configurations in both inner core and outlying areas including the capacity for transfers among different modes to promote connectivity. Ways of alleviating these pressures are identified as network adaptation including changes in and interconnections among travel mode.

The approach is based on representative systems within the seventy areas served by heavy rail, commuter rail, and light rail under the National Transit Database. First, using transit network maps, characteristics such as number of routes, end points and intersections are measured for systems within each type of the three types expanding the author’s recent work on heavy rail systems. That work found considerable structural variability among heavy rail systems in terms of the extent to which they served outlying areas and have the flexibility within the core to adapt to network outages. The transit systems within each of the three types are grouped in terms of end point coverage (system isolation) and system integration (in terms of intersections). Second, characteristics of the user population in terms of population density, race, ethnicity and income are identified to compare with system network characteristics. Third, the relative proximity of transportation routes in each of the systems to adverse environmental conditions associated with low lying areas vulnerable to sea level rise and flooding are defined. Then, the extent and characteristics of system network coverage in areas exposed to adverse environmental conditions will be compared also observing differences in service populations. Finally, opportunities that currently exist or could be used to improve the efficiency of transportation systems to adapt to these conditions will be examined in terms of current technological innovations and user behavior.