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Sight Distance (Obstruction Removal)

Insufficient sight distance and limited forward visibility can adversely affect safety and increases the risk of a collision by reducing reaction times and stopping distances. Adequate sight distance provides drivers with sufficient time to identify and appropriately react to all elements of the road environment, including other road users and hazards. Sight distances are particularly important in areas where pedestrians and bicyclists are known to cross the road.

Where visibility is restricted, sight lines should be cleared through the removal of obstructions or through road realignment. For example, the removal of vegetation or the cutting of an embankment on the inside of horizontal curves will improve sight distances. Consideration must also be given to the location and height of fences and barriers to ensure they do not obstruct visibility.

Horizontal or vertical realignment of the road may be required at crest curves, dips or on the inside of horizontal curves if adequate sight distance cannot be provided through the relocation or removal of obstructions alone. See Realignment-Horizontal and Realignment-Vertical treatment pages for further information.

If sight distance cannot be significantly improved, speed management or restrictions to vehicle movements such as right turns and overtaking may be considered along with appropriate advance warning signs.

Sight distance is also needed in other situations where drivers need to interact with other users and where there is a change in road environment. These include the approach to tunnel portals, laybys, bus stops, merging and diverging areas.  Ample sight distance is also needed on the approach to road signs so that these can be properly read by drivers.

The visual environment along a road should be planned with variety to reduce monotony. Opening up the view is desirable at scenic sections of the route and towards prominent landscape features or landmarks. This will also give a better sense of their location and progress of journey for users.

The Star Rating Demonstrator is a freely available tool with the iRAP online software, ViDA. With the Star Rating Demonstrator, it is possible to explore the impact that this Safer Roads Treatment has on risk.

Treatment Summary

Costs

Low to Medium

Treatment life

10 years - 20 years

Effectiveness

25-40%

Case Studies

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