1. Table 3 – Value of Dimension D
AS : A distance expressed in metres, determined in accordance with Clause and used for positioning of advance signs and related purposes.
Table 3 within the Code of Practice takes precedence over table 4.2 in AS
Speed of Traffic
km/h
Dimension ‘D’ m
55 or less 15
56 to 65 45
Greater than 65
Equal to speed of traffic, in Km/h
Table 3 – Value of Dimension D
Code of Practice

2. Speed of Traffic AS
1.4.16: The speed limit applying at a location or an estimate of the speed of the majority of vehicles in the stream if considered to be significantly different from the speed limit (see Note 2), either above or below.
Clause 4.1.5:
(a) The speed of traffic (see Clause ) shall be taken as either—
(i) the speed of traffic in the speed zone immediately preceding the zone in which
the advance sign occurs, see Figure 4.2(a); or
(ii) if there has been no zone change for at least the preceding 200 m, the speed of traffic at the advance sign, see Figure 4.2(b).

3. AS – figure 4.2 page 63

5. Tolerances on sign positioning
Distances may be adjusted within the below tolerances if there are items or features (eg intersections, trees etc) that do not allow the specified spacings: (a) Positioning of signs, length of tapers or markings: (i) Minimum, 10% less than the distances or lengths given. (ii) Maximum, 25% more than the distances or lengths given.
These tolerances shall not apply where a distance, length or spacing is already given in the
text or a figure as a maximum, a minimum or a range. They may need to be exceeded where
road features such as intersections or median openings intervene.
FIGURE

6. Speed limit buffer zones (CoP)
Approach Speed
Works area speed
80 km/h Speed Buffer Required
L1 (80 km/h buffer) m
L2 (60 km/h Buffer) L3
110 80 No
N/A
220 60
Yes
300
160 40
200 90
100
180 70 45
MRWA requires the values in this table to be used whenever temporary speed zones are required, unless site specific hazards are identified and the spacings need to be changed.
The objective of this section is to:
 Establish a consistent and uniform approach in the placement of temporary speed zones.
 Reduce avoidable delay to road users due to excessive and/or unnecessary temporary speed zone lengths.
 Encourage better compliance by road users to temporary speed limited areas.
 Educate road users by the standardised placement of speed zone signs.
Main Roads WA requires the values (listed in Table 2) be used whenever temporary speed zones are required, unless a site specific hazard is identified and a risk assessment determines the need to extend the sign placement. This shall be documented in the risk assessment and response table of the TMP.
Table 2 – Placement of temporary speed limit (buffer zone) signs
Code of Practice – page 30

7. 110 Km/h to 40 km/h workzone
Example – works off the road within 1.2 m of traffic lane. 110 km/h down to 40 km/h zone.

8. 110 km/h to 60 km/h workzone
Example – works off the road between 1.2 – 3 m of traffic lane. 110 km/h down to 60 km/h zone.

9. 80 km/h to 40 km/h workzone
Example – works off the road within 1.2 m of traffic lane. 80 km/h down to 40 km/h zone.

10. Risk Management Approach
A risk assessment shall always be conducted prior to determining the appropriate spacings of signs and speed zones. This shall take into account:
Road geometry
Sight distance
Road user behaviour (eg compliance to speed limit)
Traffic volume