Realignment - Vertical

A change in the vertical alignment of a road is often implicated in head-on, intersection and overtaking crashes.

Vertical road realignment may be used to

  • reduce grade (travelling down steep grades can cause brake failure, for heavy vehicles in particular, while travelling up steep grades must be done slowly in some vehicles, and can result in overtaking crashes and poor traffic flow).
  • increase the radius of a crest for adequate sight distance (by "shaving" the top off of the crest)
  • minimise vertical acceleration changes (for example, sag curves can be very uncomfortable for vehicle occupants
  • address drainage problems (water can collect in sag curves, causing a safety problem).

    Intersection approaches may be realigned vertically (or horizontally, or both) to improve sight distance. Realigning the road is costly and time consuming because it usually involves rebuilding a section of the road.

    • Reduced risk of head-on, intersection and overtaking crashes.
    • Reduced risk of vehicle equipment failure (steep grades).
    • More uniform traffic flow.
    • Vertical curve realignments require a lot of design and construction effort, and a lot of time and money. It is much better to design the road well before it is built than to rebuild it.
    • Horizontal and vertical alignments should be considered together. Poor combinations of vertical and horizontal alignment can confuse drivers and lead to dangerous situations

    Benefits

    • Reduced risk of head-on, intersection and overtaking crashes.
    • Reduced risk of vehicle equipment failure (steep grades).
    • More uniform traffic flow.

    Implementation issues

    • Vertical curve realignments require a lot of design and construction effort, and a lot of time and money. It is much better to design the road well before it is built than to rebuild it.
    • Horizontal and vertical alignments should be considered together. Poor combinations of vertical and horizontal alignment can confuse drivers and lead to dangerous situations

    Did you know?

    Unexpectedly tight horizontal bends can lead to crashes when drivers try to negotiate them at high speed.

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    Treatment Summary

    Costs
    High
    Treatment life
    20 years +
    Effectiveness
    10-25%

    References