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Simulated traffic safety in tunnels : a comparison study of traffic safety in simulated road tunnels and simulated regular road stretches

Oppers, R.L.T. (2020) Simulated traffic safety in tunnels : a comparison study of traffic safety in simulated road tunnels and simulated regular road stretches.

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Abstract:More and more tunnels are constructed in the Dutch highway network. Most of these tunnels are the ‘new generation’ landtunnels, mainly constructed for the mitigation of externalities of highways, such as noise, barrier function and air pollution. While safety is an important aspect when constructing new roads, construction of more tunnels comes with the question if the new designed tunnels are safe. Often, tunnel safety research is about operational safety, such as fire safety, escape routes and emergency exits. However, traffic safety is an important aspect because tunnels can be considered as a special object in the road, with specific effects on driver behaviour. Traditionally, safety assessment is based on accident data of a comparable road lay-out. However, tunnels are always tailor-made products, so this is not possible for most tunnels. Rijkswaterstaat has developed alternative methods that assess safety in a qualitative way, performed by qualified auditors. However, a quantitative approach to assess traffic safety in tunnels does not exist. This creates research gap in knowledge that can be filled with new insights. Changed behaviour in and around tunnels can cause conflicts between vehicles or even accidents. There are several aspects of tunnels that affect traffic safety. For this research, the suitable and quantifiable aspects that are used, are lane width, slopes, intensity and tunnel length. Already since the eighties of last century, research has been done on the assessment of traffic safety in a quantitative way. Researches showed that micro-simulation software can be used to assess traffic safety by using so called ‘surrogate safety measures’ (SSM). This approach is based on ‘near misses’ or ‘conflicts’. With qualitative measures, such as speed, direction, acceleration, deceleration, it is possible to calculate the number of conflicts, type of conflict and severity of conflict between vehicles. Other researchers discovered a relation between these conflicts and the number of accidents in real life. So, SSM is a way to assess traffic safety in a quantitative way. In this research, the safety impact of tunnels on traffic is determined with micro-simulation. Four Dutch highway tunnels are selected as case study. For these tunnels, the quantitative safety assessment, by using SSM, is performed and compared to a normal road stretch with similar properties. The goal of this assessment and comparison is to identify if the effects of tunnels on traffic safety can be quantified with the use of micro-simulation software and SSM and what those effects are. The research resulted in four main observations. The first observation is that the number of conflicts per vehicle increases if the intensity increases, what is expected based on the literature. This is the case for normal road stretches as well as for tunnels. The second observation is that, based on the simulated roads, tunnel length has no remarkable result on the number of conflicts. The third and fourth main observation are related to the simulated tunnel aspects. The slopes of the tunnel are recreated in Vissim using reduced speed areas. Slopes in tunnels result in a displacement of conflicts, compared to a normal road stretch. On the uphill slope, more conflicts occur, but just after the slope, less conflicts occur (after the exit of the tunnel). There is no increase in the total number of conflicts. The fourth observation is about the smaller object distance in tunnels. This is simulated by narrowing the lane width. The effect of narrower lanes is an overall increase of conflicts which are located on the location of the narrow lane. Concluding, the assessment of traffic safety in tunnels with the use of micro-simulation is possible. The safety assessment produces explainable results. However, more research is necessary and more empirical data is required to optimise the safety assessment tool and include more detailed effects of tunnels on safety. Hence, in the end, an assessment tool that assess safety will create more insight in traffic safety issues in tunnels and provides a quantitative method that can be standardized.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Programme:Civil Engineering and Management MSc (60026)
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