Identifying public transport gaps using time-dependent accessibility levels Koos Fransen a,b, ⁎, Tijs Neutens b , Steven Farber c , Philippe De Maeyer b , Greet Deruyter a,b , Frank Witlox b a Department of Industrial Engineering, Ghent University, Valentin Vaerwyckweg 1, 9000 Ghent, Belgium b Department of Geography, Ghent University, Krijgslaan 281 S8, 9000 Ghent, Belgium c Department of Human Geography, University of Toronto Scarborough, 1265 Military Trail, Toronto, ON, Canada abstract article info Article history: Received 29 January 2015 Received in revised form 16 September 2015 Accepted 17 September 2015 Available online xxxx Keywords: Transport gap Transport disadvantage Social exclusion Public transport GIS Flanders One of the concerns that has aroused much scholarly attention in transport geography lately is the extent to which public transport provision enables the less privileged population segments, especially those without pri- vately owned motorized vehicles, to participate in activities that are deemed normal within the society they live in. This study contributes to this line of inquiry by proposing a methodology for identifying public transit gaps, a mismatch between the socially driven demand for transit and the supply provided by transit agencies. The methodology draws on the latest accomplishments in the field of modeling time-continuous, schedule- based public transport accessibility. Accessibility levels to key destinations are calculated at regular time inter- vals, and synoptic metrics of these levels over various peak and off-peak time windows are computed for week- days and weekends. As a result, a temporally reliable picture of accessibility by public transport is constructed. The obtained index of public transport provision is compared to a public transport needs index based on the spatial distribution of various socio-demographics, in order to highlight spatial mismatches between these two indices. The study area consists of Flanders, which is the northern, Dutch-speaking region of Belgium. The results indicate that mainly suburban areas are characterized by high public transport gaps. Due to the time-variability of public transport frequencies, these gaps differ over time. © 2015 Elsevier B.V. All rights reserved. 1. Introduction The past two decades have witnessed a large and growing academic and policy interest in the social implications of transport planning alongside the traditionally well-studied economic and environmental outcomes (Lucas, 2012). Understanding the ways in which inadequate or lack of mobility can contribute to social disadvantage and isolation has been brought to the forefront of the transport policy agenda. Cur- rently, there is a wide recognition that transport policies may generate spatially and temporally uneven accessibility effects that unduly favor certain population groups above others (Grengs, 2015). One of the concerns that has recently aroused much scholarly atten- tion is the extent to which public transport provision enables the less privileged population segments, especially those without privately owned motorized vehicles, to participate in activities that are deemed normal within the society they live. Various studies conducted under the umbrella domain of transport-related social exclusion have used geographical information systems (GIS) to unravel the connections be- tween social disadvantage, public transport needs and public transport provision. However, much of the empirical work to date has explored these connections by examining social disparities in access to the public transit system rather than by the transit system. For example, in their assessment of the impact of bus network changes on different social groups in Northern Ireland, Wu and Hine (2003) suggested the use of public transport accessibility levels (PTAL) which essentially express accessibility as the sum of walking time to the closest bus stop plus av- erage waiting time at that stop. Likewise, Currie (2010) applied a com- bined indicator of access to public transit stops (e.g., spatial coverage of walk catchments around public transport stops/stations) and their rela- tive service (e.g., the number of bus/tram/train vehicle arrivals per week). While such indicators are insightful in identifying socio-spatial differences in access to the public transport system, they do not provide insights into whether the system brings people to desired activity loca- tions within an acceptable travel time at the desired time of day. Fur- thermore, these indicators ignore that inadequate proximity to public transport provision can be compensated by local availability of ameni- ties. Other recent studies that link transit access to social disadvantage like Delmelle and Casas (2012) assumed that public transport vehicles ride at a constant travel velocity in order to be able to construct a routable walk-transit network layer. Their multimodal approach accounted for ingress and egress time, but ignored wait and transfer times leading to an underestimation of the overall journey travel time. Other cognate studies have calculated end-to-end travel times by public Journal of Transport Geography 48 (2015) 176–187 ⁎ Corresponding author at: Krijgslaan 281 S8, 9000 Ghent, Belgium. E-mail address: Koos.Fransen@UGent.be (K. Fransen). http://dx.doi.org/10.1016/j.jtrangeo.2015.09.008 0966-6923/© 2015 Elsevier B.V. All rights reserved. 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