Multi-occupation segregation through London's tube network

Social segregation occurs in and through space (Shen, 2019; Wong and Shaw, 2011). The public transport system, an essential component of urban activity space, reshapes the way people are co-present when they move in and out of the network and when they remain in the carriages passing through the network (Batty, 2013). Stations and carriages are new public spaces where social segregation is perceived. The configuration of the public transport network, therefore, is not a background upon which travelling flows are projected but a foreground in which transport-related social segregation is reproduced and constrained.

Commuting is one of the highest frequency travelling behaviours in our daily lives. This article investigates social segregation in and through London's tube network during peaks within a multigroup context. We measure two types of multigroup segregation for the nodes and edges of the tube network, in-segregation and through-segregation, referring to the segregation experienced by commuters in stations when they enter or leave and the segregation perceived by those in the tube carriages moving between stations, respectively. Two components are considered: density and diversity effects. More specifically, in the multigroup segregation index, we incorporate the number of commuters (N) and the normalised entropy of the subgroups of the population (E) in an exponential function ( N E ) as the base and exponent, respectively. This index is then assigned to the nodes and edges of the public transport network, showing a reciprocal of segregation. The data used are the origin–destination commuting flow data by National Statistics Socioeconomic occupations and mode extracted from 2011 UK census data. We simulate the flows of each occupation travelling from areas with more than 0.1% of commuters using the tube to commute in London by minimising the transfer times and travel hours in the shortest distance algorithm. The flows for tube users in different occupations are then applied to compute the segregation index for every node (station) and edge (tube segment) in London's tube network.

The results are documented in a refined London tube map, shown in Figure 1. The width of segments shows the through-segregation levels, where the more segregated a segment is, the thinner it will be. The size of the station nodes reflects in-segregation, where smaller nodes are characterised by greater in-segregation. Inconsistency exists between the in-segregation distribution and through-segregation pattern for London's tube network. For in-segregation, Green Park, Oxford Circus and Bond Street are the three stations with the lowest levels, followed by Knightsbridge, Bank, and Leyton. Transfer stations and those in the city centre, however, are not always socially inclusive. Some nodes that are close to the end of the line are also highlighted as having a lower degree of segregation, e.g., Heathrow Terminals, Walthamstow Central, Brixton, Morden, Lewisham, etc. As in-segregation is mainly experienced by commuters who live or work nearby, the land-use pattern around the stations is a vital factor determining the variation in segregation. In the line-wise comparison, Metropolitan Line is detected to be the most segregated due to the co-presence of the smallest average flow size and local entropy for various occupations, while Victoria Line is outstanding for having the lowest average levels of segregation characterised by the largest mean number of commuters and mean entropy scores for all segments. Overground is highlighted as a segregated line due to the small size of its flows despite a higher level of average inter-occupation balance. Some segments in the central areas are much more socially segregated than their neighbouring segments, as they are relatively less used by people in different groups during peak hours, e.g., the segments between Baker Street and Oxford Circus via Regent's Park.

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Figure 1.

The segregated tube – multi-occupation segregation in and through London's tube network during peak hours in 2010.

This study uses commuting flow data for London via the true tube system by occupation to quantify the multigroup segregation patterns in nodes and segments of the tube network and maps them in a schematic representation – ‘the Tube’. The segregation morphologies in and through the tube network clearly demonstrate that segregation in public transport is jointly determined by the configuration of the tube network and the interconnected land-use distribution. A station or segment with more people is not necessarily more socially inclusive. The scope of this work is, to the best of our knowledge, normally absent from segregation research and neglected by transport planning. This research provides an approach to access the social performance of the public transport network in a multigroup social context, which can be useful for previewing relevant policies at the node and segment scales. The public transport space is one of the ‘third’ places between homes and the workplace and should not be overlooked, and it requires visualisation tools to measure, interpret and plan.