Integration with IMP
The Decision Support Process and the Integrated Modelling Platform are complementary components of TPRAF. This page sets out how they work together, including which IMP outputs each of the six DSP processes draws on.
The division of labour
| Decision Support Process | Integrated Modelling Platform | |
|---|---|---|
| Provides | The decision-making structure | The analytical capability |
| Through which | Problems are identified, risks assessed, interventions developed and options evaluated | Future conditions are simulated, system impacts quantified, and the consequences of alternative decisions evaluated |
| Produces | The questions that need answering | The evidence that answers them |
What the DSP asks
The DSP defines the questions that require investigation:
- Which assets, networks or services are of concern?
- What planning horizons should be considered?
- Which uncertainties should be explored?
- Which future climate, demand or operational scenarios should be assessed?
- What risks require investigation?
- What interventions are being proposed?
- What outcomes are being sought?
What the IMP supplies
The IMP supports the DSP by providing evidence relating to:
| Evidence | Documented in the IMP handbook |
|---|---|
| Climate and weather scenarios | Climate scenarios |
| Hazard occurrence and severity | Hazard models |
| Future transport demand | Transport demand |
| User behaviour and mobility patterns | Social behavioural impacts |
| Infrastructure deterioration | Transport supply |
| Transport-system disruption | Transport model |
| Economic, environmental and social impacts | Performance metrics |
| Consequences of alternative interventions | Adaptation measures |
The IMP's distinctive contribution
A key function of the IMP is to quantify how asset deterioration, disruption and intervention options affect the wider transport system, its users, and the services it provides.
That reach beyond the individual asset is precisely what the DSP's own modules cannot establish. An asset-level assessment can tell you a bridge will fail; only a system model can tell you what that does to the journeys that depend on it.
Either one can be used alone
The DSP can operate without the IMP where sufficient evidence already exists. Equally, individual IMP components may be used independently of the DSP.
But the value is in the combination
The handbook states that the greatest value is achieved when the two are used together, allowing decisions to be informed by quantified evidence rather than assumptions alone.
Stage by stage
The role of the IMP varies throughout the DSP. In some stages it describes future conditions and uncertainties; in others it quantifies the consequences of deterioration, disruption or intervention. The interaction therefore changes as the decision progresses.
1. Asset / Network Evaluation
The IMP provides evidence relating to:
- Climate scenarios
- Weather variables
- Hazard models
- Transport demand
- Transport supply
- Transport-system performance
- Impact assessment metrics
These support evaluation of current and future system performance, resilience, capacity and risk, and provide evidence on the potential consequences of deterioration, disruption and failure across the wider transport system.
2. Problem Framing and Scope
IMP outputs help stakeholders understand:
| Future operating conditions | What the system will have to cope with |
| System vulnerabilities | Where it is weak |
| Potential future constraints | What will limit the options |
| Emerging risks and pressures | What is coming that is not yet a problem |
This supports the identification, prioritisation and definition of problem statements, helping ensure that subsequent activity focuses on the issues of greatest significance.
3. Risk Reduction Analysis
The IMP supports understanding of:
- Consequences of deterioration
- Consequences of disruption
- Consequences of system failure
- Potential risk-reduction benefits
This helps determine whether identified risks are acceptable, and supports assessment of risk-reduction strategies by quantifying the consequences of different future outcomes.
4. Detailed Option Assessment
The IMP can be used to evaluate:
- The impacts of alternative interventions
- Changes in transport performance
- User impacts
- Economic impacts
- Environmental impacts
- Social impacts
- Network-level consequences
This enables comparison of alternative interventions using quantified evidence.
5. Portfolio Optimisation
The IMP can be used to assess:
- Multiple intervention portfolios
- Different implementation timings
- Future demand scenarios
- Alternative climate futures
This is where the IMP earns its keep
Comparing portfolios under different future conditions is what identifies robust strategies: those that perform well across multiple climate, demand and disruption scenarios, rather than only under the single future that was assumed.
A portfolio optimised for one projected future is a bet. One tested across several is a strategy.
6. Outcome Assessment
The IMP can be used to compare predicted and observed outcomes, and support learning from implemented interventions. That information is then fed back into future iterations of both the DSP and the IMP.
The interaction is iterative, not linear
This is the point the handbook returns to most often.
The DSP identifies the problems, risks and intervention options requiring investigation. The IMP quantifies future conditions, system impacts and the consequences of the alternatives. The resulting evidence is then used to:
- Refine assumptions that proved wrong or too coarse
- Modify interventions in light of how they performed
- Reassess risks against the quantified consequences
- Evaluate whether predicted outcomes are acceptable, before progressing
Only then does the process move to the next DSP stage.
The loop runs in both directions
Outputs produced by the IMP inform decisions within the DSP, while decisions made within the DSP define the scenarios, interventions and questions to be explored within the IMP.
Neither is upstream of the other in any permanent sense.
This feedback is what enables interventions, assumptions and strategies to be tested, refined and reassessed before implementation, improving the robustness and transparency of decision-making.
A missing figure
The source handbook refers to Figure 6.1, illustrating the interaction between the DSP and the IMP, and the caption is present in the document. The figure itself was never inserted, so it cannot be reproduced here.
It is one of two missing figures in the handbook. The other is Figure 2.1, the overview of the DSP embedded within TPRAF.
Further reading
The IMP has its own handbook covering the nine components in full. Start at the IMP introduction, or go directly to the framework overview, which carries the conceptual diagram the IMP is built around.