Model validation

The method proposed to validate the model is by Expert intuition, where an expert who has knowledge about the system evaluates the model outputs and behaviour. The first step of the validation was to collect data of a project to be used in the model. Since it was not possible to find data of a real project, experts have made “educated guess” and suggested figures for two fictitious projects in the city of Rotterdam. The next step was to validate the results of the model by experts,

76 based on their experience. The details of the projects used for the Excel model validation, the input data and the results are presented in Appendix H.

Project 1: Nieuwe Binnenweg

The project 1 is located in a shopping/residential street in the region of Delfshaven in Rotterdam consisting of around 500 domiciles. The street is two-way and allows the flow of cars and tramways. The pipeline that needs rehabilitation is located under the sidewalk and consequently no road closure is needed for the open trench or trenchless methods. It is assumed that most of the parking spaces in the area are under subscription for residents and only 10% of them are open for the public. From those, half of the parking spaces are unavailable during open trench execution. Besides, the open trench option causes a pedestrian sideway closure. The trenchless option does not affect the parking availability or pedestrian flow. It is supposed that the loss of parking space and pedestrian walkway closure will impact business revenue by 10% for the open trench option. Regarding the reduction of pavement service life, the pavement degradation fee of 25€/m2 is adopted for sideway concrete tiles.

Figure 16: Nieuwe binnenweg in Rotterdam. Source: Google Maps , 2017

Project 2: Volmarijnstraat

The project 2 is located in a residential street in the region of Delfshaven in Rotterdam. There are approximately 200 domiciles located there. The street is one-way and does not allow tramway transit. The pipeline that needs rehabilitation is located under the road in the middle of the street and therefore a complete road closure is needed in the open trench option. For the trenchless option, only around the manholes will be blocked and therefore partial closure is needed. The pedestrians will not be affected in any case and therefore no pedestrian delay is predicted. All the parking spaces are

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reserved for residents with a subscription and therefore it is assumed that the hourly rate is much lower than a normal parking place. Regarding pavement service life reduction, the degradation fee adopted is 32€/m2 for non-asphalt roads.

Figure 17: Volmarijnstraat in Rotterdam. Source: Google Maps , 2017

This project information was used as input data for filling in the Excel model and calculating the social costs and risks. Once the results for the projects were generated, two experts from Rotterdam Municipality were consulted to validate the results and the model. At this point, the experts compared the outputs of the model with values/forecasts they would have expect based on their experience.

The results obtained for both projects are consistent with what would be expected in reality. The (fixed) social costs are higher for the open trench options in both cases. For instance, the pavement service life reduction is higher in the open trench options due to a larger volume of excavation. The noise pollution is also higher due to a longer project duration and a higher number of affected domiciles when open trench is used. The trenchless option also generates noise, but fewer domiciles are affected since the machines are located in specific areas on the site instead of throughout the whole street like in the excavation.

In project 1, no road closure is needed and therefore no traffic delay is expected. However, in many cases the pipeline is located under the road pavement which might require a total or partial lane closure. This situation would lead to detours and most probably traffic delays, especially in open trench projects. Some pedestrian delay is also expected in project 1 for both methods; however the longer project duration for the open trench option will lead to higher pedestrian delay costs.

In project 2, the open trench and trenchless methods will require complete and partial lane closure, respectively. Consequently, there will be some delay time and traffic delay costs. These delay costs are higher for the open trench option due to the longer project duration and the traffic management

78 plan. The traffic delay costs are not very significant in project 2 because the traffic flow, the delay time and duration of street obstruction are low. In large projects, traffic delay costs can amount more than 50% of the total social costs (Matthews and Allouche, 2010).

The social costs of project 1 are much higher compared to project 2 because the former is located in a shopping street. Consequently, some loss of business revenue is expected during the project 1 execution due to the loss of accessibility to customers. Higher losses would be likely if the street was completely closed during a longer period of time.

Concerning risks, in project 1 the five risks criteria (risk of accidents workers; accidents users; damage to property/infrastructure; damage to buried pipelines; damage to environment) scored higher for the open trench option. Consequently, the overall risk score was also higher for the open trench compared to trenchless option (overall score 3 against 2). The same situation happened in project 2, where the overall score for open trench was 2 and for trenchless 1.

The results indicate that the risks related to the five risk types are higher for open trench considering the factors affecting risks described in this research. These results do not represent a risk assessment, but just an indication of which option is risker in terms of likelihood.

When comparing the overall risk scores of the projects, project 1 which is located in a shopping/residential area presented a higher score for both methods in comparison to project 2. This result is expected based on literature and experts consultations: busier areas tend to present more risks due to the higher flow of pedestrians, traffic, presence of buildings and so on. In these situations, the likelihood of accidents and damage are higher especially if the projects last long and many machines are on site.

In the fictitious projects described above, the main social costs relate to loss of business revenue, pavement service life reduction, noise pollution and loss of parking space. The data used came from educated guess made by experts, and therefore other values could have been suggested leading to different results. The particularities of the projects under analysis are reflected on the social costs results for both open trench and trenchless methods.

The validation conducted in this research aimed at verifying (1) which social costs and parameters should be included in the model and (2) whether the model satisfies the objectives defined at the start of this research, mainly to quantify/monetize social costs. The outputs obtained from the model, based on the two project cases, were realistic according to the experts.

Another validation comparing the model outputs and real/standard values could not be performed. Even though there are many social cost models proposed in literature, there is not much standardization among them and as a consequence the parameters used in the equations are not compatible. Therefore, the validation performed was subjective in the sense that it was only based on the opinions of experts.

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