Cambridgeshire
The Cambridgeshire case study asks a focused question: which road links become most vulnerable to rainfall as demand grows?
It answers it without agent-based simulation, by combining a demand projection with an empirically estimated rainfall sensitivity.
The workflow
Step 1: Assemble the inputs
Base-year traffic volumes from National Highways WebTRIS are combined with four further datasets:
| Input | Source |
|---|---|
| Base-year traffic volumes | National Highways WebTRIS |
| Population projections | ONS |
| Employment data | BRES |
| Development allocations | Greater Cambridge Local Plan |
| Road distances | OpenStreetMap, calculated using OSRM |
Step 2: Project demand with the gravity model
These inputs are used in the gravity model to:
- Estimate changes in accessibility between 2024 and 2045
- Produce projected traffic demand for 329 Strategic Road Network sensor sites
Step 3: Apply the resilience model
The projected demand is then combined with observed and future rainfall information in the GLM Resilience Model to estimate:
- Link-level rainfall sensitivity
- Future traffic speeds
Step 4: Map the result
The resulting spatial outputs can be mapped to identify the road links most vulnerable to rainfall-related disruption under combined future demand and climate conditions.
What makes this case study distinctive
Two futures at once, not one
Most vulnerability assessments vary one thing. This varies two: the network carries more traffic and faces a changed climate.
A link can be comfortable under today's demand in heavy rain, and under 2045 demand in dry conditions, while failing under both together. Combining the projections is what surfaces that.
Breadth over depth, by design
Compare this with North East England, which simulates individual travellers through a modelled flood.
Cambridgeshire covers 329 sensor sites with a single measure, speed sensitivity. North East England covers one conurbation with 32 metrics. Neither approach would substitute for the other, and the IMP runs both.
Where the components are documented
| Component | Chapter |
|---|---|
| The gravity model and its five inputs | Transport demand: inputs and outputs |
| The GLM Resilience Model | Resilience tool |
| WebTRIS, ONS, BRES, OSRM sourcing | Resilience tool: inputs |