Urban growth, new economic activities, infrastructure and mobility projects change the way a city and their citizens interact. To assess changes based on the above factors, we use the concept of social fragmentation for two different periods. We propose a methodology that evaluates the degree of social fragmentation in different zones of Bogotá and the impact of the introduction of a Bus Rapid Transit system (BRT). The fragmentation analysis shows an increase in interactions for the three different income groups analysed in the 1995–2005 comparison. The spatial distribution of defragmented zones has also changed. Peripheral zones were isolated in 1995, close to ghettos or closed community concept, while in 2005 their interactions with the city saw an important improvement. The difference in difference analysis shows that feeder lines, serving specially those peripheral zones, have a positive impact on population as the fragmentation indicator decreases. However, no evidence was found regarding trunk line zones.