This presentation discusses the temporal dimension of accessibility and its application in detecting causes of low accessibility. It reviews existing approaches to measuring accessibility over time and how new data sources can help capture temporal changes in land use, individual movement, and transportation networks. As a case study, it uses speed profiles and public transit data to analyze job accessibility in Madrid at different times of day and under different transportation scenarios. The temporal analysis helps identify specific constraints on accessibility like congestion levels, routing networks, and frequency of public transit.