1 - HKU Libraries

T.P.D.M. V.2.3
(Al/2001)
3.9.3.36 The detailed design for the required length of safety fence to shield the hazard can be
referred to Roadside Design Guide and Road Design Guide.
3.9.3.37 As a rough guide based on the recommendations from the above references, Table 3.9.3.2
shows the suggested flare rates for safety fence.
Table 3.9.3.2
Suggested Flare Rates (1 :x) for Safety Fence
Speed Limit
Flare rate for safety fence beyond shy line
Weak post system with
compacted earth footing
Strong post system
with concrete footing
Flare rate for safety
fence inside shy line
110
15
20
30
100
15
20
30
90
12
16
25
80
11
15
21
70
10
12
18
60
10
10
16
50
10
10
15
Clearance between Barrier Fences and Carriageway
3.9.3.38 The horizontal clearance of barrier fences from carriageway should follow the requirements
set out in Section 3.5.2 of this chapter.
3.9.3.39 Concrete profile barrier should not be set back more than 3500 mm from the edge of the
carriageway to reduce the severity of impacts occurring at high angles.
Parapet
3.9.3.40 A parapet is a structural component installed along the edge of a bridge or similar structure
intended to prevent vehicles or pedestrians from falling off. For types, details and uses of
parapets, refer to Chapter 15 of the Structures Design Manual for Highways and Railways.