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Step 3 is about mapping the intervention logic – the causal chain between the services provided, their expected outcomes and longer term impacts, identifying both intended and unintended consequences and how these might be measured. An ‘intervention logic map’ is used to illustrate the relationship between the intervention and the impacts. A table is helpful for creating this, and summarising for each service:
• Inputs – the investment in resources and activities
• Outputs – for example, the target groups reached, number of in-vehicle units to be installed, the software to be created (such as for generating messages)
• Outcomes – the short and medium term results such as changes in traffic flow or speed, journey times
• Impacts – the longer term results such as improvements in safety and environmental benefits.
Step 4 involves defining the purpose of the evaluation, the primary and secondary impacts of the use cases to be investigated and then formulating the research questions and the hypotheses to be tested. The measures (or indicators) to be used to answer these research questions are then defined, covering both quantitative and qualitative measures. It is helpful to be able to compare results between different C-ITS trials, which is feasible if indicators are designed to be comparable with those used in other trials.
As an example, the research questions for a Road Works Warning service may include:
• What is the effect on the speed of the equipped vehicle at the point that the road works start? (Do equipped vehicles reduce risk for road workers?)
• What is the effect on the speed of the equipped vehicle on approach to the road works? (Do drivers in equipped vehicles brake earlier?)
• What is the effect on the speed of upstream vehicles?
• What were the driver’s opinions of the service?
The data to inform these research questions are expected to include: Speed of equipped vehicles at the start of road works (source: GPS data logging); Speed at intervals on approach to the road works (source: GPS data logging); Speed of upstream vehicles (source: video or loop data); and Drivers’ opinions of the service
In addition to these detailed metrics, key indicators for the trial data are expected to include:
• Road safety – Number of fatalities
• Road safety – Number of serious injuries
• Road safety – Number of slight injuries
• Road safety – Damage cost of injury collisions
• Travel time – Total time spent travelling and also the proportion of total time, that is ‘lost vehicle hours’
• Fuel consumption – Money spent on petrol (excluding tax)
• Fuel consumption – Money spent on diesel (excluding tax)
• Greenhouse gas emissions – CO2.
