Kerbs and kerb stones

Barrier kerbs are steep-faced and are designed to prevent vehicle encroachment on the roadside. Their main functions are:                                                                              

• to discourage vehicles from using areas outside the travelled way, not intended for vehicular travel;

   

  
  
   
• to control drainage;

   

  
  
   
• to control parking of vehicles;

   

  
  
   
• to reduce the risk to pedestrians.

The typical barrier kerb is 150mm high. This height is effective to prevent vehicle encroachment into the roadside at low to moderate speeds.

Barrier and semi-barrier kerbing should generally be avoided on freeways or highways with design speeds of over 70 km/h because impact with kerbing on high-speed roads may overturn a vehicle or result in a vehicle becoming airborne.

Barrier-type kerbs may be used on sections of road where separation of opposing traffic is essential due to the high safety risks associated with traffic volumes, percentage of heavy vehicles, speed, crash history etc.

If a design allows for kerbed shoulders with barrier type kerbing the shoulder width should be adequate to accommodate a disabled vehicle (eg. AASHTO recommends a min of 1.8m; Austroads recommends a minimum width of 2.0m). The desirable shoulder widths for rural and outer urban roads are shown in Main Roads Supplement to Austroads GRD Part 3: Geometric Design - Table 4.3.

Barrier kerb, if positioned along the edge of a traffic lane, gives drivers a sense of restriction. Also large vehicles travelling along kerbed carriageways have no additional space in which to manoeuvre or to allow for sway of the rear trailer. It is recommended to avoid this type of kerbing on roads with restricted lane width and high percentage of heavy vehicles.

Barrier kerbs reduce the risk to pedestrians, not only as a physical but psychological barrier as well, because drivers generally tend to shy away from the kerb line.  For this reason, barrier kerbing is recommended in built-up areas adjacent to footpaths with considerable pedestrian traffic, shared use paths and also at bus bays.

Barrier-type kerb may be used on low speed (< 70 km/h) arterial roads in order to prevent mid-block turns.

Some of the above text was adopted from AASHTO's Policy on Geometric Design of Highways and Streets (2004).