Source: https://www.mainroads.wa.gov.au/BuildingRoads/StandardsTechnical/RoadandTrafficEngineering/GuidetoRoadDesign/Pages/MRWA_Supplement_to_Austroads_Guide_to_Road_Design___Part_4A.aspx
Timestamp: 2017-10-18 13:17:47
Document Index: 76280663

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MRWA Supplement to Austroads Guide to Road Design - Part 4ACurrently selected
Document No: D11#308726
Revision: 1Q
The information below is intended to reflect the preferred practice of Main Roads Western Australia ("Main Roads"). Main Roads reserves the right to update this information at any time without notice. If you have any questions or comments please contact Nick De La Motte by e-mail or on (08) 9323 4448.
3.2.1 & 3.2.3
Tables 3.1 & 3.2 corrected. 21-Dec-2011
Drawings 200531-0006 and 200531-0007 amended. 02-Feb-2012
Drawings 200531-0006 and 200531-0007 amended. 11-Feb-2012
New Clause 4.1 "General" added. 09-Aug-2012
Figure 4.22 - Separation Line removed.
​1F ​6.2.3 Drawings 200131-0084, 200131-0085 and 200131-0086 amended. 22-Nov-2012
​1G ​6.2.1 ​Figure 6.1 - Text "Edge of Shoulder" amended to "Edge of Lane". ​17-Apr-2013
​Contact person changed to Kyle Smith. ​16-May-2013
​1I ​4.1 & 4.6 Links to Roadtrains at Rural Intersections Drawings added.
Figure 4.22 updated. ​19-Jun-2014
​Figure 4.22 amended. ​23-Jun-2014
​Reference Figure 10.10 Example (a) and (b) - Position of stop line for motor vehicle lane changed from 4m to 5m. Example (d) - Length of the bicycle head start storage facility changed from 4m to 5m. ​03-Oct-2014
​Re-link drawings 200531-0006 and 200531-0007. ​06-Oct-2014
​1M ​4.6 ​1st paragraph amended. ​18-Aug-2015
​1N ​9.2 & 9.3 ​Drawing 200731-0071 amended. ​16-Jun-2016
​1O ​6.2 ​Table 6.2 Minimum island widths amended. ​01-Aug-2016
​1P ​10.6.4 ​Drawings 200531-0006 and 200531-0007 amended. ​08-Aug-2016
​1Q ​Header ​Contact person changed to Nick De La Motte ​25-Jan-2017
MRWA Supplement to Austroads Guide to Road Design Part 4A - Unsignalised and Signalised Intersections
4. TYPES OF INTERSECTIONS AND THEIR SELECTION
4.6 Auxiliary Lane Turn Treatments (Type AU)
4.7 Channelised Turn Treatments (Type CHR)
4.8 Warrants for BA, AU and CH Turn Treatments
6. TRAFFIC ISLAND AND MEDIANS
7. RIGHT-TURN TREATMENTS - LAYOUT DESIGN DETAILS
9. U-TURN TREATMENTS
10. SIGNALISED INTERSECTIONS
10.4 Sight Distance
Part 4A - Unsignalised and Signalised Intersections
This Supplement has been developed to be read as a supplement to the Austroads Guide to Road Design (GRD) Part 4A: Unsignalised and Signalised Intersections (2009), a copy of which can be purchased via the Austroads website.
In Western Australia, state-based information, in this website and elsewhere, takes precedence over Austroads Guides and Standards Australia Standards.National Guides and Standards take precedence over International Guides and Standards, unless specifically stated otherwise.
This Supplement has the same structure as the equivalent Austroads Guide and only additional requirements, clarifications, or practices different from Austroads appear.Where appropriate, this Supplement may also contain additional sections and figures not covered by Austroads, but the numbering sequence found in the Austroads Guide remains. Figures and tables in this Supplement replace those with the same figure or table number in the equivalent Austroads Guide.
This guideline applies to all new works on roads managed by Main Roads. It is noted that many existing intersections were constructed to the design standards of the time and do not necessarily meet all current design requirements. Whilst it is not economically feasible to upgrade existing intersections each time revisions are made to design standards, Project Managers should consider making improvements whenever major works are completed in the vicinity of existing intersections.
It is important for Road Planners and Designers to be aware of the effects that different types of intersection control may have on delays to traffic (under various traffic demand situations) and the resultant emissions. A range of factors should be taken into consideration when deciding the most appropriate traffic management treatment at any given intersection. These are outlined in the Guide to Road Design Part 4B: Roundabouts, the Guide to Traffic Management Parts 3 and 10, and the Main Roads Supplement to Austroads Guide to Road Design Part 4 - Intersections and Crossings - General.
The general requirement is that the maximum grade for at least the last 30m from the intersection edge of pavement is 3%. It is good practice that this requirement is applied at all intersections - particularly where there are a high number of trucks.
Reference Figure 2.6, Approach Sight Distance (ASD) is the minimum level of sight distance to be provided at intersections. ASD is measured from a driver's eye height (1.1m) to object height (0.0m), which ensures that a driver is able to see any line marking and kerbing at the intersection.
Refer to Main Roads Supplement to Austroads GRD Part 3: Geometric Design, Section 7.7.12.
In addition to the sight distance requirements in Austroads GRD Part 4A, the following sight distance checks should be made:
intersections with restricted lateral sight distance (for stopping sight distance);
intersections on or near crest vertical curves (for approach sight distance);
on approaches to speed change and lane drop areas (for approach sight distance);
on the approaches to underpasses (for stopping sight distance); and
on the approaches to railway level crossings (for approach sight distance)
Intersections should be positioned in safe locations using the Sight Distance criteria in Section 3.2. The sight distance values shown in Table 3.1 of the Austroads documents should be increased generally for design on unsealed roads. Refer to Australian Road Research Board - Unsealed Roads Manual, Guidelines to Good Practice (August 2009).
Where it is unreasonable or extremely difficult to achieve ASD, then as an absolute minimum, Stopping Sight Distance (SSD) should be provided.
In the application of Table 3.1, the following guidance is provided:
A reaction time of 2.5s shall be used as the Main Roads desirable minimum and a reaction time of 2.0s shall be used as the Main Roads absolute minimum.
Absolute minimum reaction time should not be used in combination with other minimum design standards.
A reaction time of 1.5 seconds shall not be used in Western Australia.
Based on approach sight distance for a car1
h1 = 1.1, h2 = 0, d = 0.362
RT = 2.0s
RT = 2.5s
Truck stopping capability
minimum crest curve size3
d = 0.22, h1= 2.4m, h2= 0m
Table 3.1 Approach sight distance (ASD) and corresponding minimum crest
vertical curve size for sealed roads (S<L)
Notes to Table 3.1:
If the roadway is on a grade, calculate the approach sight distance (ASD) values using the correction factors in Table 3.3 (or use Equation 1 in Section 3.2.1) by applying the average grade over the braking length.
A coefficient of deceleration (d) of 0.36 shall be used in Western Australia.
This check case assumes the same combination of design speed and reaction time as those listed in the table, except that the 120 km/h and 130 km/h speeds are not used.
Refer to the Austroads GRD - Part 3: Geometric Design (2009) to determine the ASD for trucks around horizontal curves.
In the application of Table 3.2, the following guidance is provided:
Based on safe intersection sight distance for a car1
h1 = 1.1, h2 = 1.25, d = 0.362
Minimum SISD
capability provided
by the crest
vertical curve size3
d = 0.29, h1= 2.4m, h2= 1.25m, observation time = 3.0s
Table 3.2 Safe Intersection sight distance (SISD) and corresponding minimum crest
Notes to Table 3.2:
If the roadway is on a grade, calculate the safe intersection sight distance (SISD) values using the correction factors in Table 3.3 (or use Equation 2 in Section 3.2.2) by applying the average grade over the braking length.
These check cases assume the same combination of design speed and reaction time as those listed in the table.
3.2.3 Minimum Gap Sight Distance (MGSD)
Safe Intersection Sight Distance should be provided at driveways in accordance with Table 3.2. However, where this is not possible due to constraints, sight distance equal to the Stopping Sight Distance for the design speed of the road shall be provided as an absolute minimum.
In relation to Roadtrains at Rural Intersections, Main Roads has developed some typical layouts which can be found in Guideline Drawings 201431-0001 and 201431-0002.
Reference Figures 4.5 and 4.6, Main Roads does not support the use of lane separation line at AUR intersections.
A typical type AUR treatment is illustrated in the Figure 4.22 below. Note that the widening (diverge) taper radii shall be designed as per the radii shown therein.
Figure 4.22: Typical Main Roads Type AUR treatment
Reference Figure 4.7, Main Roads does not support the use of the tapered flares at the left turn out of the minor road. Left turn corners should be based on the swept path of the design vehicle.
The type CHR(S) treatment is not a preferred Main Roads treatment.
In the application of Figure 4.9, Main Roads prefers to use the AUR treatment as an alternative to the Type CHR(S).
4.11.1 Rural Staggered T-Intersection Treatments
Reference Figure 4.16(a,) Main Roads does not support the use of the staggered treatment.
4.12.1 Rural Seagull Treatment
Reference Figure 4.19, Continuity lines are not used through merge areas in Western Australia.
5.3.1 Components of Deceleration Turn Lanes
Reference Figure 5.1, Main Roads preferred practice is for 100m radius back to back coincident reverse curves to be applied to the diverge taper.
5.4.3 Merge Taper TM
Main Roads has adopted a merge rate of 0.6 m/s at all auxiliary lane tapers.
5.4.4 Other considerations
For specific requirements relating to merge tapers refer to Main Roads Supplement to Austroads GRD Part 3: Geometric Design Chapter 9.9.2 Tapers.
6.2 Raised Traffic Islands and Medians
Refer to Main Roads Supplement to Austroads GRD Part 3: Geometric Design - Section 4.7. Raised islands on the centre line of the side road (minor road) approaching intersections are referred to as splitter islands by Main Roads. Raised islands on the centre line of the main carriageway (major road) are referred to as medians by Main Roads.
6.2.1 Raised Islands
Splitter Islands (excluding roundabout and corner approach islands) shall be constructed as shown in Figure 6.1. The island width ('W') and refuge gap ('X') can be determined from Table 6.3, after assessing usage by pedestrians and cyclists or a combination of both.
Figure 6.1. Splitter Island Geometry
The values in Table 6.2, "Desirable minimum" column should be used wherever possible. The length (L) of the splitter island shall be determined from Austroads - Guide to Road Design Part 4A (Oct, 2009) Section 6.2.2. Table 6.2.
Island/Median used for protection/refuge
Island width 'W'
Gap in island
'X' Min (m)
Desirable Minimum (m)
Absolute Minimum (m)
Signs or street lighting
Signals1- single aspect width ​2.0 ​1.5 ​2.5
Signals1- dual aspect width ​2.5 ​2.0 ​2.5
Separate traffic flows and a rigid safety barrier
Separate traffic flows and a flexible safety barrier
Shelter turning vehicles and traffic signals
Table 6.2 Minimum island widths
Notes to Table 6.2:
1 For traffic signals, the minimum offset to any part of the signal is 0.6m from the kerb face
This Table replaces Austroads Tables 6.2 & 6.3
6.2.3 Raised High Entry Angle and Free-flow Left-turn Islands
There are two corner approach island types:-
High entry (70o) angle island, and
Free flow slip lane (directional) island
Examples of the use of these islands are shown on drawings 200131-0084, 200131-0085 and 200131-0086. The High entry angle island shall be designed using the criteria shown in Figure 6.2.3.1. Note that if cut through pedestrian access is to be used rather than pedestrian ramps, it is recommended that the minimum island size be increased from 6.0m by 12.0m to 8.0m by 15.0m.
Figure 6.2.3.1. High Entry Angle Island
Where an exclusive cycle lane runs adjacent to an island, the island may be placed parallel to the cycle lane with a 0.3m offset as shown in Figure 6.2.3.2 provided the cycle lane width exceeds the 0.2m per 10km/h offset criteria.
Figure 6.2.3.2. High Entry Angle Island with Adjacent Cycle Lane
The free flow slip lane island shall be designed using the criteria shown in Figure 6.2.3.3 and must exit into its own lane on the cross road. The island has an extended parallel departure nose which ensures that vehicles are aligned correctly in the acceleration lane prior to merging.
Figure 6.2.3.3. Free Flow Slip Lane Island
An alternative shown at Figure 6.2.3.4 shows a cycle lane cutting through the island to cross to the left of the acceleration lane at 90 degrees.
Figure 6.2.3.4. Free Flow Slip Lane Island with Cycle Lane
Figure 6.2.3.5 shows a left turn island for use only when the left turn movement is signalised.
Figure 6.2.3.5. Left Turn Island for Signalised intersection
Seagull islands are used in the median opening at 'T' intersections - where the median width is 10 metres or greater - to fill the large expanse of pavement and give direction to turning traffic. The seagull island shall be designed using the criteria shown in Figure 6.2.3.6.
An example of this is shown on drawing 200131-0085.
Figure 6.2.3.6. Seagull Island (Minimum Island Area 10m2)
Where intersections include kerbed medians or kerbed islands, street lighting should be provided.
6.4 Desirable Clearance to Traffic Islands and Medians
To enable stopped vehicles to be passed, the desirable minimum through carriageway width between kerbs is 6.0m. The absolute minimum through carriageway width between kerbs is 5.5m. The desirable minimum width for single lane one-way traffic carriageways (including shoulder) should be 6.0m with an absolute minimum width of 5.5m.
6.5 Road Widths between Kerb and between Kerb and Safety Barrier
Main Roads requires a 0.5m clearance beyond the swept path (which includes vehicle body overhang) of the design vehicle to the face of kerb.
6.6 Kerb and Channel
Main Roads preferred practice is not to use kerb and channel.
Refer to the Policy on U-turns at Intersection Traffic Lights guideline, for Main Roads requirements.
9.2 Rural Roads
Refer to Main Roads Drawing 200731-0071 for details of signs and pavement markings.
9.3 Urban Roads
10.3.2 Proximity to Other Intersections
Main Roads does not use Minimum Gap Sight Distance (MGSD).
10.5.2 Service Road Treatments to Other Intersections
Reference Figure 10.3 the following treatments are not preferred practices used by Main Roads:
In the top left quadrant, the egress should be separated by a minimum length of 10m of parallel kerb.
In the bottom right quadrant, the egress from the service road blending into the taper for the left turning lane should be separated by a minimum length of 10m of parallel kerb.
10.6.3 Pedestrian Treatments
Reference chapter: Pedestrian crossings
match the pedestrian ramp width (minimum = 2.5m); and
where necessary, be wide enough (e.g. = >5.0m) to accommodate high pedestrian demands."
10.6.4 Cyclist Facilities
Reference Figure 10.10 Example (a):
Main Roads position the stop line for motor vehicles 5m back from the adjacent bicycle stop line (in accordance with Main Roads Standard Drawing 200531-0006), not 2m as shown in the example.
Reference Figure 10.10 Example (b):
Main Roads position the stop line for all motor vehicle lanes 5m back from the bicycle stop line (in accordance with Main Roads Standard Drawing 200531-0006), not with the through / right motor vehicle lanes further forward than the left turn lane as shown in the example.
Reference Figure 10.10 Example (c):
Main Roads does not support the use of exclusive right turn lanes for bicycles. The right turn head start storage facility would be accessed via the exclusive bicycle lane located to the left of the leftmost through lane. Refer to Main Roads Standard Drawings 200531-0006 and 200531-0007 for further details. Right turn head start storage facilities for bicycles are not used where there are more than one through lane for motor vehicles.
Reference Figure 10.10 Example (d):
Main Roads does not support the use of Hook Turn facilities for bicycles. Refer also to Figure 10.11. The length of the bicycle head start storage facility shall be 5m in accordance with Main Roads Standard Drawings 200531-0006 and 200531-0007. Right turn head start storage facilities for bicycles are not used where there is more than one through lane for motor vehicles.
Reference Left-turn bypass treatment
Main Roads does not support the use of left turn bypass facilities (as shown in Figure 10.12), due to land constraint issues and conflict with services. Proposals to use such facilities shall be treated on a case by case basis taking into account the aforementioned issues and interaction with other road users such as pedestrians.
Reference Bypass of T-intersection
Main Roads does not support the use of bypass treatments at intersections. Proposals to use such facilities shall be treated on a case by case basis and may result in modification to the treatment shown in Figure 10.13.
APPENDIX A EXTENDED DESIGN DOMAIN (EDD) FOR INTERSECTION TURN TREATMENTS
Application of EDD will require the explicit approval of Manager Road and Traffic Engineering.
APPENDIX B CRASH TYPES AT UNSIGNALISED INTERSECTIONS
APPENDIX C TRUCK STABILITY AT INTERSECTIONS
APPENDIX D SET-OUT DETAILS FOR HIGH-ENTRY ANGLE CHL
APPENDIX E SWEPT PATHS FOR ROAD TRAINS AT HIGH ENTRY ANGLE LEFT-TURN TREATMENTS