# Horizontal curves on approach to large roundabouts

**URL:** <https://forum.irap.org/t/horizontal-curves-on-approach-to-large-roundabouts/1035>\
**Category:** Coding\
**Created:** [July 29, 2024, 4:39am UTC](https://forum.irap.org/t/horizontal-curves-on-approach-to-large-roundabouts/1035 "2024-07-29T04:39:50Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![paul.crowe](https://forum.irap.org/letter_avatar_proxy/v4/letter/p/35a633/32.png) [@paul.crowe](https://forum.irap.org/u/paul.crowe)\
**Post date:** [July 29, 2024, 4:39am UTC](https://forum.irap.org/t/horizontal-curves-on-approach-to-large-roundabouts/1035/1 "2024-07-29T04:39:50Z")

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A well-designed roundabout will have an approach curve (entry curve) of less than 200m (Austroads recommendation). This is what helps reduces speeds and impact angles at a roundabout and contributes to good safety outcomes (reduced severity). The question is should these tight horizontal curves be coded within the curvature road attribute? I have seen some coding where this has occurred, but I would be concerned with this approach as it significantly increases the Run-Off and Head-On crash scores to the point where it would make well designed roundabout undesirable.

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**Author:** ![james.bradford](https://forum.irap.org/letter_avatar_proxy/v4/letter/j/dc4da7/32.png) [@james.bradford](https://forum.irap.org/u/james.bradford)\
**Post date:** [August 2, 2024, 7:18am UTC](https://forum.irap.org/t/horizontal-curves-on-approach-to-large-roundabouts/1035/2 "2024-08-02T07:18:14Z")

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Hi Paul,

You are right to question roundabout approach’s being coded as curves.  
Deflecting the approach to a roundabout is an important part of a roundabouts safety benefit. So they should not be coded as curves.

regards

James