Providing appropriate sight lines and sight distances (also referred to vision lines and vision distances) are a key factor in ensuring the safe operation of roads, junctions and development accesses, and are usually required by local planning authorities as part of submitting a development related planning application. TTRSA can undertake speed surveys and associated calculations to determine the appropriate distances.
Sight lines in urban areas are usually specified within the Design Manual for Urban Roads and Streets (DMURS). For non-national roads outside urban areas they are specified by development standards within City and County Development Plans For national road they are specified within Transport Infrastructure Ireland (TII) Standards including DN-GEO-03043 "Geometric Design of Major/Minor Priority Junctions and Vehicular Access to National Roads".
Sight lines are comprised of two main elements: firstly, visibility splays from an access point often expressed in 'x' and 'y' distances; and, secondly, forward visibility, often expressed in terms of stopping sight distances (SSDs).
For sight lines, clear visibility is required in the horizontal plane which can be impacted by for example, walls, trees, posts, bends etc., and also vertical plane which is typically impacted be the height of roadside features like walls, hedges and banks, and also crests formed by the carriageway.
In urban areas sight lines often need to take account of other road users such as pedestrians on footways and cyclists on cycle tracks. Inter-visibility between road users can often mean the difference between a relatively safe environment and an environment where collisions occur and result in injury.
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