Assessing how road network interventions impact both safety and emissions at the same time is a challenging task, even at a singular study area, while assessing the transferability of these impacts to new study areas is even harder to perform. To that end, this paper introduces the concept of the Impact Modification Factor (IMF), expressed as the fluctuation of the examined impacts before and after interventions. IMFs offer a top-down indicator to compare different scenarios by demonstrating how much a measure affects an impact relative to existing conditions. In this study, IMFs were estimated separately for emissions, iRAP star rating results, and road safety indicators, ensuring consistency with the corresponding simulation and iRAP results. This methodology was applied to road sections of the Athens urban network to explore how selected interventions influence safety outcomes and pollutant emissions, within the context of the Phoebe Project. Three scenarios were implemented in a traffic simulation environment: (i) the baseline, (ii) an intervention scenario with infrastructure changes, and (iii) an intervention scenario with infrastructure changes and a zonal 30 km/h speed limit reduction. The infrastructure changes include modifications to geometry, lane layout, and traffic management. Each simulation produced information on flow, speed, and travel time for every road section. Using these outputs, the London Emission Model (LEM) estimated CO₂ and NOₓ emissions, reported in grams for each segment. Road safety was analysed separately through the iRAP protocol. Specifically, each segment was described by its key physical and operational features, such as lane width, number of lanes, intersection type, and speed limit. The iRAP model then generated Star Rating Scores (SRS) and Fatal and Serious Injury (FSI) indicators for pedestrians, cyclists, motorcyclists, and vehicle occupants. All datasets were merged using a common identifier, ensuring that every segment carried both safety and emission data. The IMF was then derived for each case. For safety indicators, a value above one indicated improvement compared with the baseline, whereas for emission indicators, a value above one represented deterioration, since higher values correspond to increased pollutant levels. Out of two hundred ninety-one segments, ninety-six featured IMF values under one, showcasing network improvements. Two-lane arterials presented the largest number of improvements, whereas wider divided roads showed mixed results. In certain central corridors, such as along Fillelinon and Vasilissis Amalias, IMF values for the iRAP and road safety indicators were above one, demonstrating the benefits of the interventions. In contrast, narrower sections with more consistent traffic flow tended to show positive changes in both emissions and safety indicators. By using IMFs, comparisons between design alternatives become more straightforward, since both environmental and safety outcomes are expressed on a single scale. The approach also helps reveal cases where one goal improves at the expense of the other, giving decision-makers a clearer view of trade-offs that might otherwise remain unnoticed. Moreover, IMFs facilitate the transferability of results of one road network sub-section to another, when segments are comparable, in order to have an initial rough estimate of how interventions might affect the road environment.
| ID | pc679 |
| Presentation | |
| Full Text | |
| Tags |
