SNAMUTS Indicators
The Spatial Network Analysis for Multimodal Urban Transport Systems (SNAMUTS) methodology has been developed as a planning and decision-making support tool. It determines accessibility performance from a user perspective, bearing in mind that different users sometimes have different needs: some may value speed more than anything else, some may require barrier-free access as their first priority, others may be drawn primarily to services that are legible and have a high profile in the urban realm. Good accessibility is often the result of a balance and integration of these sometimes competing, sometimes complementary claims on the useability of the land use-transport system.
The analysis includes a set of tasks and measurements that highlight the contribution of public transport network and service development from a range of perspectives. These are known as the eight key SNAMUTS indicators (see below). In addition, there is a composite index and an efficiency change measure.
Service intensity
What is the number of public transport services required to achieve an optimal level of accessibility across the network, noting that the resources may be limited?
Closeness centrality
What is the ease of movement offered on public transport across the city and for each route? Fast and/or frequent services reduce ‘spatial resistance’ to the user compared to slow and/or infrequent services.
Degree centrality
What is the transfer intensity of the network? While transfers are a necessary component of an integrated public transport system, is there a way of measuring whether their occurrence may be excessive or underdeveloped?
Network coverage
What is the percentage of residents and employees within walking-distance to public transport services at a standard that allows for both planned and spontaneous trip making across most hours of the day, seven days a week?
Contour catchments
What is the geographical range users can cover by way of a public transport journey within a particular time frame, and how many destinations are located within this range?
Betweenness centrality
How does the public transport network channel, concentrate and disperse the travel opportunities generated by the interplay of land uses and the transport system?
Resilience
Where on the network do these effects result in a potential mismatch between public transport supply and potential demand?
Nodal connectivity
How well is each activity centre connected in order to attract stopovers on public transport chain journeys and encourage land use intensification to capitalise on such flows of people?
Composite Accessibility Index
How can the results of these indicators be calibrated to arrive at a comparative scale for public transport accessibility between different cities and within one city over a time line?
Key Assumptions and Definitions of SNAMUTS
The core methodology of SNAMUTS was originally inspired by the Space Syntax theory (Hillier and Hanson, 1984) and by the Multiple Centrality Analysis tool (Porta et al, 2006a, 2006b). In this understanding, networks can be characterised by a topological aspect, examining the degrees of separation between a pair of objects, measured in changes of direction, passages through doors or gateways, or (in public transport networks) numbers of transfers. In contrast, the metric aspect examines the objects’ distance from each other, expressed either in common measurements of distance (kilometres, miles) and/or by a proxy measure (travel time, travel cost, ease of movement).
Operationalised for analytic output, these categories inform the concepts of degree centrality and closeness centrality, a terminology used frequently in the analysis of networks (Neal, 2013) and adopted for the SNAMUTS indicator set with some important variations. This is because the relationship between movement and urban form is different in public transport networks than in those for individualised modes of transport: Public transport distributes patrons through a limited number of access points (rail stations or bus stops) and patrons cannot frequent intermediate land uses in the same way as pedestrians, cyclists or (with some constraints regarding the cost and availability of parking) motorists.
Underground rail passengers are also visually removed from what occurs above ground in land use terms. Public transport access points thus assume a particularly prominent role in the land use-transport system both from the perspective of public transport users, and of policy makers seeking to enhance the significance of the mode. A useful way to understand this context is to see public transport access points in terms of both nodes and places (Bertolini, 1999).
Bertolini’s ‘node-place model’ notes that while railway stations provide access to the transport network, which he defines as the ‘node’ element in his model, they also offer a ‘place’ function. The railway station precinct can also be a destination where land use activities are available to public transport users and others. The place function, or accessibility of opportunity, is an important aspect of this study requiring accessibility to be understood not only in terms of ‘ease of movement’ or ‘degrees of separation’. The extent of concentration of activities around public transport facilities as well as within a specific travel time range to and from each destination emerge as equally critical factors in understanding accessibility. These concepts inform the SNAMUTS measures of network coverage and contour catchments.
In the node-place model the observation that there can be ‘balanced’ or ‘unbalanced’ node-places is also important. A balanced node-place benefits from a good match between the level of transport network accessibility and the mix of activities (opportunities) to access within the precinct. In this way both the transport network and the place are efficiently used. An unbalanced node suffers from good transport network access but a limited number and range of activities, while an unbalanced place will be characterised by a vibrant mix and concentration of activities but poor transport network access.
Further, node-places can experience stress where both node and place functions are exceptionally high, generating pressures such as transport network and interchange congestion, strong market demand for further land use intensification and increasing property values (Bertolini, 2005). To examine and quantify these dynamics, SNAMUTS returns to a concept from the Multiple Centrality Analysis toolbox known as betweenness centrality (Porta et al, 2006a, 2006b). This set of measures aims to assess and visualise how the distribution of land uses in a settlement area and their interdependence generate travel opportunities in accordance with the spatial configuration and service levels of the public transport network. This study also focusses specifically on the phenomena of stress and resilience in the land use-transport system by deriving a dedicated network resilience measure from the betweenness results.
A Matrix of Activity Nodes
To produce a set of accessibility indicators for a land use-transport system, SNAMUTS assesses the hierarchy of central places in an urban area. Strategic planning documents can assist with the identification of district, regional or neighbourhood centres (where there are clusters of employment, retail, education or health facilities, recreational uses and/or large concentrations of residences). A matrix of central places and nodes is compiled as each potential origin-destination pair is subjected to a GIS-based way-finding procedure.
An activity centre is included if it is spatially associated with a particular public transport access point or interchange and if its walkable catchment (an 800-metre radius for rail stations and ferry ports or a 400-metre corridor around surface routes) contains an average minimum of 10,000 residents and jobs. However, major public transport transfer points are generally included in the matrix even where they are located away from land use clusters (the ‘unbalanced node’ archetype).
Minimum Service Standard
Public transport network elements are included where they meet a minimum level of service. This rationale relates to user amenity. To be perceived as a regular service where transport users can organise both planned and spontaneous activities, public transport must allow for a degree of flexibility in personal schedule (i.e. run at a minimum frequency) and maintain a presence throughout the day and week (i.e. have operational hours that cover most or all potential travel purposes).
For the examples shown on this website, the minimum standard applied (SNAMUTS 23) requires that surface modes (bus and light rail) have service frequencies of 20 minutes or better during the weekday inter-peak period (from 10:00am to 3:00pm) and 30 minutes or better on weekends. It also requires that segregated (rail and ferry) modes provide services seven-days-a-week, with service frequencies of 30 minutes or better on weekdays. The differentiation in service standards between modes with or without dedicated right-of-way reflects the ability of rail stations and ferry terminals to act as anchors for urban activities and attractors for land use development in their own right, an effect that tends to be significantly weaker with surface routes, particularly on-street buses.
Many conventional models of public transport performance focus on the weekday peak hours, since this is usually the period when the capacity constraints of a network become most apparent. In most public transport systems, this is also the period when service levels are optimised to facilitate specific trip purposes (such as work and school journeys). In contrast, the weekday inter-peak period offers the greatest diversity of travel purposes and is the best determinant of whether public transport can offer a viable alternative to the ‘go anywhere, anytime’ convenience of the car.
References
Bertolini L (1999) Spatial development patterns and public transport: the application of an analytical model in the Netherlands. Planning Practice and Research, Vol 14, No 2, pp 199-210
Bertolini L (2005) Cities and Transport: Exploring the Need for New Planning Approaches. Chapter 5 in (eds) Albrechts L, Mandelbaum S J (2005) The Network Society. A New Context for Planning. Oxford: Routledge.
Hillier B, Hanson J (1984) The Social Logic of Space. Cambridge: Cambridge University Press.
Neal Z P (2013) The Connected City. How Networks Are Shaping the Modern Metropolis. New York: Routledge
Porta S, Crucitti P, Latora V (2006a) The Network Analysis of Urban Streets: A Dual Approach. Physica A, Statistical Mechanics and its Applications, Vol 369, No 2
Porta S, Crucitti P, Latora V (2006b) The Network Analysis of Urban Streets: A Primal Approach. Environment and Planning B: Planning and Design, Vol 33, pp 705-725
The Spatial Network Analysis for Multimodal Urban Transport Systems (SNAMUTS) methodology has been developed as a planning and decision-making support tool. It determines accessibility performance from a user perspective, bearing in mind that different users sometimes have different needs: some may value speed more than anything else, some may require barrier-free access as their first priority, others may be drawn primarily to services that are legible and have a high profile in the urban realm. Good accessibility is often the result of a balance and integration of these sometimes competing, sometimes complementary claims on the useability of the land use-transport system.
The analysis includes a set of tasks and measurements that highlight the contribution of public transport network and service development from a range of perspectives. These are known as the eight key SNAMUTS indicators (see below). In addition, there is a composite index and an efficiency change measure.
Service intensity
What is the number of public transport services required to achieve an optimal level of accessibility across the network, noting that the resources may be limited?
Closeness centrality
What is the ease of movement offered on public transport across the city and for each route? Fast and/or frequent services reduce ‘spatial resistance’ to the user compared to slow and/or infrequent services.
Degree centrality
What is the transfer intensity of the network? While transfers are a necessary component of an integrated public transport system, is there a way of measuring whether their occurrence may be excessive or underdeveloped?
Network coverage
What is the percentage of residents and employees within walking-distance to public transport services at a standard that allows for both planned and spontaneous trip making across most hours of the day, seven days a week?
Contour catchments
What is the geographical range users can cover by way of a public transport journey within a particular time frame, and how many destinations are located within this range?
Betweenness centrality
How does the public transport network channel, concentrate and disperse the travel opportunities generated by the interplay of land uses and the transport system?
Resilience
Where on the network do these effects result in a potential mismatch between public transport supply and potential demand?
Nodal connectivity
How well is each activity centre connected in order to attract stopovers on public transport chain journeys and encourage land use intensification to capitalise on such flows of people?
Composite Accessibility Index
How can the results of these indicators be calibrated to arrive at a comparative scale for public transport accessibility between different cities and within one city over a time line?
Key Assumptions and Definitions of SNAMUTS
The core methodology of SNAMUTS was originally inspired by the Space Syntax theory (Hillier and Hanson, 1984) and by the Multiple Centrality Analysis tool (Porta et al, 2006a, 2006b). In this understanding, networks can be characterised by a topological aspect, examining the degrees of separation between a pair of objects, measured in changes of direction, passages through doors or gateways, or (in public transport networks) numbers of transfers. In contrast, the metric aspect examines the objects’ distance from each other, expressed either in common measurements of distance (kilometres, miles) and/or by a proxy measure (travel time, travel cost, ease of movement).
Operationalised for analytic output, these categories inform the concepts of degree centrality and closeness centrality, a terminology used frequently in the analysis of networks (Neal, 2013) and adopted for the SNAMUTS indicator set with some important variations. This is because the relationship between movement and urban form is different in public transport networks than in those for individualised modes of transport: Public transport distributes patrons through a limited number of access points (rail stations or bus stops) and patrons cannot frequent intermediate land uses in the same way as pedestrians, cyclists or (with some constraints regarding the cost and availability of parking) motorists.
Underground rail passengers are also visually removed from what occurs above ground in land use terms. Public transport access points thus assume a particularly prominent role in the land use-transport system both from the perspective of public transport users, and of policy makers seeking to enhance the significance of the mode. A useful way to understand this context is to see public transport access points in terms of both nodes and places (Bertolini, 1999).
Bertolini’s ‘node-place model’ notes that while railway stations provide access to the transport network, which he defines as the ‘node’ element in his model, they also offer a ‘place’ function. The railway station precinct can also be a destination where land use activities are available to public transport users and others. The place function, or accessibility of opportunity, is an important aspect of this study requiring accessibility to be understood not only in terms of ‘ease of movement’ or ‘degrees of separation’. The extent of concentration of activities around public transport facilities as well as within a specific travel time range to and from each destination emerge as equally critical factors in understanding accessibility. These concepts inform the SNAMUTS measures of network coverage and contour catchments.
In the node-place model the observation that there can be ‘balanced’ or ‘unbalanced’ node-places is also important. A balanced node-place benefits from a good match between the level of transport network accessibility and the mix of activities (opportunities) to access within the precinct. In this way both the transport network and the place are efficiently used. An unbalanced node suffers from good transport network access but a limited number and range of activities, while an unbalanced place will be characterised by a vibrant mix and concentration of activities but poor transport network access.
Further, node-places can experience stress where both node and place functions are exceptionally high, generating pressures such as transport network and interchange congestion, strong market demand for further land use intensification and increasing property values (Bertolini, 2005). To examine and quantify these dynamics, SNAMUTS returns to a concept from the Multiple Centrality Analysis toolbox known as betweenness centrality (Porta et al, 2006a, 2006b). This set of measures aims to assess and visualise how the distribution of land uses in a settlement area and their interdependence generate travel opportunities in accordance with the spatial configuration and service levels of the public transport network. This study also focusses specifically on the phenomena of stress and resilience in the land use-transport system by deriving a dedicated network resilience measure from the betweenness results.
A Matrix of Activity Nodes
To produce a set of accessibility indicators for a land use-transport system, SNAMUTS assesses the hierarchy of central places in an urban area. Strategic planning documents can assist with the identification of district, regional or neighbourhood centres (where there are clusters of employment, retail, education or health facilities, recreational uses and/or large concentrations of residences). A matrix of central places and nodes is compiled as each potential origin-destination pair is subjected to a GIS-based way-finding procedure.
An activity centre is included if it is spatially associated with a particular public transport access point or interchange and if its walkable catchment (an 800-metre radius for rail stations and ferry ports or a 400-metre corridor around surface routes) contains an average minimum of 10,000 residents and jobs. However, major public transport transfer points are generally included in the matrix even where they are located away from land use clusters (the ‘unbalanced node’ archetype).
Minimum Service Standard
Public transport network elements are included where they meet a minimum level of service. This rationale relates to user amenity. To be perceived as a regular service where transport users can organise both planned and spontaneous activities, public transport must allow for a degree of flexibility in personal schedule (i.e. run at a minimum frequency) and maintain a presence throughout the day and week (i.e. have operational hours that cover most or all potential travel purposes).
For the examples shown on this website, the minimum standard applied (SNAMUTS 23) requires that surface modes (bus and light rail) have service frequencies of 20 minutes or better during the weekday inter-peak period (from 10:00am to 3:00pm) and 30 minutes or better on weekends. It also requires that segregated (rail and ferry) modes provide services seven-days-a-week, with service frequencies of 30 minutes or better on weekdays. The differentiation in service standards between modes with or without dedicated right-of-way reflects the ability of rail stations and ferry terminals to act as anchors for urban activities and attractors for land use development in their own right, an effect that tends to be significantly weaker with surface routes, particularly on-street buses.
Many conventional models of public transport performance focus on the weekday peak hours, since this is usually the period when the capacity constraints of a network become most apparent. In most public transport systems, this is also the period when service levels are optimised to facilitate specific trip purposes (such as work and school journeys). In contrast, the weekday inter-peak period offers the greatest diversity of travel purposes and is the best determinant of whether public transport can offer a viable alternative to the ‘go anywhere, anytime’ convenience of the car.
References
Bertolini L (1999) Spatial development patterns and public transport: the application of an analytical model in the Netherlands. Planning Practice and Research, Vol 14, No 2, pp 199-210
Bertolini L (2005) Cities and Transport: Exploring the Need for New Planning Approaches. Chapter 5 in (eds) Albrechts L, Mandelbaum S J (2005) The Network Society. A New Context for Planning. Oxford: Routledge.
Hillier B, Hanson J (1984) The Social Logic of Space. Cambridge: Cambridge University Press.
Neal Z P (2013) The Connected City. How Networks Are Shaping the Modern Metropolis. New York: Routledge
Porta S, Crucitti P, Latora V (2006a) The Network Analysis of Urban Streets: A Dual Approach. Physica A, Statistical Mechanics and its Applications, Vol 369, No 2
Porta S, Crucitti P, Latora V (2006b) The Network Analysis of Urban Streets: A Primal Approach. Environment and Planning B: Planning and Design, Vol 33, pp 705-725
