The objective of this research was to review the literature on the obscuration problem, to construct a simulation model to assess the obscuration to drivers on a section of straight two lane dual carriageway, with subsequent modification to allow for variations in horizontal alignment and the addition of a third lane, and to measure levels of obscuration and other traffic parameters at a series of roadside locations. Roadside surveys were carried out to measure traffic flow characteristics (speed, flow, and composition), dimensions of vehicles, and obscuration periods. Sites were chosen to include both straight and curved sections of road, as well as when there was a gradient. Obscuration periods were measured by overhead or side video cameras, mounted so that obscuration could be assessed by measurements of the visibility of the drivers heads from the camera location. An assumed sign legibility distance of 200 metres was adopted. Data on 118,016 vehicles at 31 locations were collected. This was analysed via stepwise linear regression using the SPSS statistical package. For the simulation, the final model developed incorported car following and lane changing features. The results from both empirical and simulation experiments were presented and discussed.

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