Roads and traffic have a multitude of impacts on wildlife populations. Wildlife existing within the confines of fragmented reserves are particularly susceptible to fatalities on roads, especially those situated within urban and semirural matrices. The sustainability of many wildlife populations within reserve fragments are tenuous as roads further subdivide reserved areas and increase the frequency of animal–vehicle contact. Although many studies have assessed the quantity and diversity of fatalities from collisions, few studies have examined the long-term viability of wildlife populations living adjacent to roads. We chose to examine the effects of disturbances, including fatalities on roads, on a population of swamp wallabies (Wallabia bicolor) within the Royal National Park on the urban fringe of Sydney, Australia. Despite having an extensive range, researchers suspect that many local populations of this sole member of Wallabia are in decline. We used a combination of population modeling and sensitivity analysis to assess the impact of disturbances on the population. Under current conditions, the forecast of the population was to decline over the next 100 years with the possibility of becoming extinct. We found that female reproduction and breeding were most influential on the population model. Of the range of management options investigated, by far the most rewarding was the reduction of fatalities on roads, as only a 20% decrease in female fatalities on roads has the potential to reverse the current decline and represents the best option for maintaining long-term viability. We suggest that documentation and subsequent management of road impacts, within the context of other threats, is essential to the conservation of similar species in road-affected environments.