CHICANE SPECIFICATIONS   Table 1 Stagger length and car speeds Lane width 'B' (feet) Free view width 'A' (feet) Stagger length 'L' to achieve the required vehicle speed in chicane   15mph 20mph 25mph 9.84’ +3.3’ 19.7’ 29.5’ 45.9’ 0 29.5’ 42.7’ 59.1’ -3.3’ 39.4’ 52.5’ - 11.50’ +3.3’ - - 36.1’ 0 29.5’ 39.4’ 49.2’ -3.3’ 36.1’ 49.2’ 62.3’ 13.1’ +3.3’ - 23.0’ 29.5’ 0 - 29.5’ 39.4’ -3.3’ - 36.1’ 49.2’ Table 2 Minimum dimensions of stagger length for larger vehicles Stagger length 'L' (feet) needed for a free view width of 0.0 ft Lane width 9.8’ 11.5’ 13.1’ Artic. Truck 65.6’ 49.2’ 36.1’ Rigid Truck 39.4’ 29.5’ 23.0’ Bus 42.7’ 36.1’ 29.5’ NOTES: Stagger length (L) The length between the start of the stagger on the offside and the finish of the stagger on the nearside, or vice versa, for a one-way approach. Increasing the stagger length increased mean speeds. Short stagger lengths prevented the passage of large vehicles such as articulated vehicles. Lane width (B) The width of the approach lane. There was little effect on speeds when the approach lane widths were varied. The trials indicated that drivers were prepared to remain behind cyclists where it was obvious that there was insufficient space to pass. Free view width (A) The offset between the offside curb and the nearside curb as viewed through the stagger, on a one-way approach. Changing the free view width from +1m to -1m reduced mean speeds by about 10mph. Visual Restriction Obscuring forward visibility across the bulbouts. This had a positive effect in reducing speeds by 2mph to 4mph. To avoid compromising the safety of children, any barrier provided for this purpose should not be higher than 600mm. Although in the trials the barrier was built up to the carriageway edge, it will normally be preferable to provide a clearance between the barrier and the carriageway edge to avoid the barrier being struck. Reductions in speed may then be less. Return to chicane description Back to Toolbox