|
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
