Transport supply
Transport supply represents the capacity of transport systems offered to move people or goods within a specific region.
Where transport demand describes who wants to travel and when, supply describes what they have to travel on.
In agent-based modelling
Within agent-based transport modelling, supply is represented as a digital geospatial network through which individual travellers and vehicles undertake their simulated journeys (Alvarez Castro, 2024).
What the network describes
A transport supply network is typically a digital geospatial network describing two things.
Physical infrastructure
- Roads
- Railways
- Airports
- Other transport facilities
Public transport services
- Routes
- Stops
- Service frequencies
- Timetables
Together these provide the spatial and operational structure through which travel between activities is simulated. A commute from home to work, for instance, only becomes a journey once there is a network to make it on.
The minimum a network must contain
The methodology used to construct a transport supply network varies according to the modelling objective, spatial scale and required level of detail. There is no single correct construction.
That said, the handbook is clear about the floor. A network generally requires at minimum a georeferenced representation of the road network containing:
| Element | What it provides |
|---|---|
| Nodes | Junctions and endpoints |
| Links | The road segments between them |
| Connectivity | Which links join which nodes, and in which direction |
| Link length | Distance travelled |
| Travel speed | How fast traffic moves when free-flowing |
| Capacity | How much traffic a link can carry |
| Permitted modes | Which vehicle types may use it |
Additional layers describing public transport infrastructure and services can be incorporated where multimodal travel is represented.
Diverse methods, one hard requirement
The handbook puts it plainly: the methodology to generate a network is diverse and depends on the purpose of the model, although a minimum geospatial representation of the roads is required.
In other words, you can build the network many ways, but you cannot skip the roads.
Why supply attributes matter to the IMP
The attributes above are not bookkeeping. They are what allows a hazard to be translated into a transport consequence.
A flood map from hazard models identifies flooded ground. It is the network that says which links that ground belongs to, what capacity is lost, and which modes can no longer pass. Without link-level attributes, a hazard has nowhere to land.
What this chapter covers
| Page | What you will find |
|---|---|
| Road network | Building the road network from OpenStreetMap with MATSim |
| Public transport | PT2MATSim, GTFS sources for Great Britain, and the Transit Mapper |
| MATSim network | The complete supply file set and what it enables |
| Further reading | Guides, repositories and data sources |
Source attribution
The definition in this chapter is adapted from the doctoral thesis of Alvarez Castro (2024), available from Newcastle University Theses.