The SNAMUTS resilience measure provides a comparison between the significance of a route segment for the land use-transport system (betweenness) and the level of service provided (capacity). Where the ratio between segmental betweenness and route capacity appears to be well-matched, the network elements can be considered resilient. Where the betweenness score appears to overwhelm the carrying capacity, network elements appear to be under pressure or stress.
Note that such pressures do not necessarily manifest in instances of actual overcrowding of public transport vehicles or interchanges. A poor resilience score on a service with sparse real-life patronage may also be indicative of ‘latent demand’. Conversely, a good resilience score on this index is no guarantee that overcrowding will never occur on the segment; for instance, it may derive from travel generators other than residences and workplaces.
Network resilience is visualised on a network map using traffic light colours and a scale where a positive score between 0-30 (green) is considered resilient, a negative score between 0 and -30 (yellow-orange) a cause for concern and a score below -30 (red-maroon) under stress.
Resilience
where:
Rk = Segmental resilience index of segment k
Pij(k) = Paths between nodes i and j that pass through route segment k
acti = Number of residents and jobs in catchment area of node i
actj = Number of residents and jobs in catchment area of node j
Lmin,ij = Minimum cumulative impediment between nodes i and j
fk = Service frequency along route segment k
ck = Modal coefficient for route segment k
Bg = Global betweenness index
N = Number of activity nodes in the network
The nodal resilience value, displayed on resilience maps added since 2018, is calculated by determining a nodal average of the median segmental resilience values along all journey paths between the reference node and all other nodes on the network, weighted by catchment size and travel impediment (like the betweenness index). Nodal resilience conveys a sense of the pressures on public transport accessibility in each location. Positive (green) values suggest that public transport to and from the node in question has spare capacity for patronage growth. Negative (yellow, orange and red) values indicate that some public transport journeys to and from these nodes may be subject to overcrowding and/or a poor public transport market share.
Note that such pressures do not necessarily manifest in instances of actual overcrowding of public transport vehicles or interchanges. A poor resilience score on a service with sparse real-life patronage may also be indicative of ‘latent demand’. Conversely, a good resilience score on this index is no guarantee that overcrowding will never occur on the segment; for instance, it may derive from travel generators other than residences and workplaces.
Network resilience is visualised on a network map using traffic light colours and a scale where a positive score between 0-30 (green) is considered resilient, a negative score between 0 and -30 (yellow-orange) a cause for concern and a score below -30 (red-maroon) under stress.
Resilience
where:
Rk = Segmental resilience index of segment k
Pij(k) = Paths between nodes i and j that pass through route segment k
acti = Number of residents and jobs in catchment area of node i
actj = Number of residents and jobs in catchment area of node j
Lmin,ij = Minimum cumulative impediment between nodes i and j
fk = Service frequency along route segment k
ck = Modal coefficient for route segment k
Bg = Global betweenness index
N = Number of activity nodes in the network
The nodal resilience value, displayed on resilience maps added since 2018, is calculated by determining a nodal average of the median segmental resilience values along all journey paths between the reference node and all other nodes on the network, weighted by catchment size and travel impediment (like the betweenness index). Nodal resilience conveys a sense of the pressures on public transport accessibility in each location. Positive (green) values suggest that public transport to and from the node in question has spare capacity for patronage growth. Negative (yellow, orange and red) values indicate that some public transport journeys to and from these nodes may be subject to overcrowding and/or a poor public transport market share.
