In this article, we quantify the impact of individual and contingent factors on citizens’ decisions to regularly use the public bus transportation in Barcelona, Spain. Using data from an original survey, we approximate the effect of traffic congestion as a deterrent to becoming a high-frequent bus rider and show that level of education and employment status, as indicators of environmental concerns, fuel the regular use of bus services. Simulations conducted to identify the group of citizens most prone to changing their transportation habits additionally show that regular commuters in the urban area and with a higher level of education are more responsive to reductions in congestion that increase their probability of becoming frequent bus users.