3. MRWA Supplement to VicRoads "Managed Freeways - Freeway Ramp Signals Handbook" November 2010

Document No:  D13#15386
 
Revision:  1A
 
Date amended:  26-Nov-2013

Image: orange line.RCN-D13^23151823.GIF 

 

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 Dave Landmark by e-mail or on (08) 9323 5441.

To the extent permitted by law, Main Roads, its employees, agents, authors and contributors are not liable for any loss resulting from any action taken or reliance made by you on the information below or changes to its preferred practice.

Revision Register

 

Ed/Version Number Clause Number Description of Revision Date
1 All  Guideline Developed  30-Jul-2013
1A 2.3.1.1 Footnote added for Superscript of "auxiliary lane1" 26-Nov-2013

Table of Content


MRWA Supplement to VicRoads “Managed Freeways – Freeway Ramp Signals Handbook”, November 2010

 

Currently there are no Austroads or other national guidelines on freeway ramp signals. Main Roads has been authorised by VicRoads to use their publication “Managed Freeways – Freeway Ramp Signals Handbook, November 2010” as a primary reference. Accordingly, this Supplement has been developed to be read in conjunction with the VicRoads publication, a copy of which can be obtained via the VicRoads website
 
In Western Australia, state-based information, on 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 VicRoads publication and only additional requirements, clarifications, or practices different from VicRoads appear. Where appropriate, this Supplement may also contain additional sections and figures not covered by VicRoads, but the numbering sequence found in the VicRoads publication remains. Figures and tables in this Supplement replace those with the same figure or table number in the equivalent VicRoads publication.

 

Notations and Abbreviations

AP               Access point

pc/h/ln         Passenger cars per hour per lane
 
RP               Repeater point

veh/h           Vehicles per hour
 
veh/h/ln       Vehicles per hour per lane
 
 

Chapter 1 - Safe, Reliable and Efficient Freeway Operation

 

1.1 Managed Freeways - Introduction

 
Perth’s freeway network carries 20% of the vehicle-kilometres of travel on the road network although comprising only 4% of the road network length. The efficient use of freeways is essential in providing a safe and reliable level of service that maximises the productivity of the asset and provides optimum operation in relation to throughput and travel time.
 

1.2 Freeway Ramp Signals – An Overview

 
Main Roads proposes to use the HEuristic Ramp metering co-ordination (HERO) suite of algorithms to provide coordinated dynamic management of Perth’s freeways. For more details refer to Section 7.6 of the VicRoads publication.
 

1.3 Context within an Integrated System


Managed freeways with coordinated freeway ramp signals operate within the strategic context for Managed Freeways in WA as shown in Figure 1.2.
 
Image: Figure 1.RCN-D13^23109372.GIF 
Figure 1.2: Strategic Context for Managed Freeways in WA
 
 
 

1.4 Background

Main Roads is currently in the project development stage for a Managed Freeways Pilot Project.

 
 
 

Chapter 2 - Principles of Freeway Traffic Flow

 

2.3.1.1 Bottlenecks


In WA, where a lane drop is required at a freeway ramp exit, the practice has traditionally been to carry the lane past the ramp nose and then instigate the lane drop. The rationale behind this is to avoid a “trapped lane” situation which may result in drivers changing lanes at the last second, or worse, driving across the gore area.

The usually accepted capacity of a two lane section on a managed freeway for design purposes is 2,000 veh/h/ln (equivalent to 2,100 pc/h/ln).  A lane drop is a source of turbulence and research has shown that a midblock lane drop can cause a capacity drop in an unmanaged freeway of 10 to 20%, i.e., result in a capacity of 1,800 veh/h/ln to 1,600 veh/h/ln. There is a lack of research on this matter in relation to lane drops after an exit; however it is not unreasonable to assume a capacity drop of 10% i.e., a two lane capacity on the mainline of 3,600 veh/h.
 
It has been found that if the lane drop is provided as an exclusive exit lane, provided sufficient advance warning of the exclusive exit is given, (enabling drivers to move into the correct lanes well in advance of the exit), then the loss of capacity is minimised. From a design point of view therefore, it is important that consideration be given to capacity implications of lane layout arrangements and how a lane drop is effected in order to minimise turbulence and optimise the freeway capacity. For appropriate ramp spacing guidelines, the designer should refer to Austroads Guide to Traffic Management, Part 6 - Intersections, Interchanges and Crossings.

In the case of weaving sections, the Highway Capacity Manual may be used as an initial guide to determine what type of lane drop may be appropriate, subject to the proviso below.

Based on research by Burley, appropriate maximum capacity values for freeway design should be:
    • Unmanaged freeways: 1,800 pc/h/ln (typically 1,700 veh/h/ln) which accepts a low risk of flow breakdown
    • Managed freeways: 2,100 pc/h/ln (typically 2,000 veh/h/ln) with well-designed infrastructure and a state-of-the-art coordinated ramp metering system, eg VicRoads HERO algorithm

In any analysis therefore for both weaving sections and off-ramps, in the case of lane drops after the exit, the through-traffic volume should not exceed 90% of the above values due to the expected turbulence.
 
The following guidelines may be used to determine whether or not an effective lane drop could be achieved through the provision of an exclusive exit lane. 
 

For all lane drops
    • In the case of a three-lane freeway upstream of the exit, if the exiting traffic volume is approximately 1/3 or more of the approach volume, then an exclusive exit lane may be appropriate. (Based on the Highways Agency guidelines, if the exiting volume is greater than 1,350 veh/h then a two-lane exit may be more appropriate).
    • In the case of a four-lane freeway upstream of the exit, if the exiting traffic volume is approximately 1/4 or more of the approach volume, then an exclusive exit lane may be appropriate. (Based on the Highways Agency guidelines, if the exiting volume is greater than 1,350 veh/h then a two-lane exit may be more appropriate).


The lane to be dropped is an auxiliary lane1

    • If the distance between the adjacent upstream on-ramp and the exit is short (< 450m between “edges meet” points) and the weaving volumes are relatively light (< 1000 veh/h) then an exclusive exit lane may be appropriate.
    • If the distance between the adjacent upstream on-ramp and the exit is short (< 450m between “edges meet” points) and the weaving volumes are relatively heavy (> 1000 veh/h), the majority of which originates from the adjacent upstream on-ramp, then an exclusive exit lane may not be appropriate.

1 An auxiliary lane in the freeway context is a lane that starts at an on-ramp (normally as an added lane) and ends at the adjacent downstream off-ramp (normally as a lane-drop).

 

The lane to be dropped is not an auxiliary lane

    • If the distance between the adjacent upstream on-ramp and the exit is short (< 450m between “edges meet” points) and the entering ramp weaving volumes are relatively light (< 500 veh/h) then an exclusive exit lane may be appropriate.
    • If the distance between the adjacent upstream on-ramp and the exit is short (< 450m between “edges meet” points) and the entering ramp weaving volumes are relatively heavy (> 1000 veh/h) then an exclusive exit lane may not be appropriate.
    • If the provision of an exclusive exit lane means that traffic entering from an adjacent upstream on-ramp or traffic entering from the ramp immediately upstream of that has to make more than one lane change in order to proceed beyond the exit ramp and the distances between the ramps are relatively short (< 750m between nose of onramp to exit ramp nose), then an exclusive exit lane is not appropriate [refer to Figure 2.3(a)].

 

Image: Figure 2.RCN-D13^23109370.GIF 

 

Figure 2.3(a): Example of Inappropriate Exclusive Left Turn Lane

 

 

2.3.3 Recovery from Flow Breakdown


Figures 2.9(a) and 2.9(b) show an example of flow breakdown and recovery on the Mitchell Freeway at the northbound lane drop from 3 to 2 lanes immediately after the Hepburn Avenue exit on Tuesday 10 August 2010. The Time-Distance plot in Figure 2.9(a) shows slow-moving traffic with worsening speed values from green to yellow to orange to red.  Note that while flow breakdown also occurs at the Hepburn Avenue on-ramp merge, the flow breakdown occurs first at the lane drop.
 
 
Image: Figure 2.RCN-D13^23109368.GIF 
 
Figure 2.9(a): Flow Breakdown and Recovery on Mitchell Freeway Northbound
 (Average speeds)
 
 
Another way to show the flow breakdown and recovery is given in Figure 2.9(b). Each data point represents the average flow and speed for one minute. The points are connected in time sequence. The chart shows that flow breaks down from 15:07 to 15:09 resulting in significantly lower average speeds and flows. Flow recovery occurs from 18:34 to 18:36 when the average speed increases to around 90km/h under lower flow conditions.
 
 
 Image: Figure 2.RCN-D13^23110037.GIF
 
Figure 2.9(b): Flow Breakdown and Recovery on Mitchell Freeway Northbound (Speed vs Total Flow)
 
 

Chapter 3 - Principles of Freeway Ramp Metering

 

3.1 A Managed Freeway System

 
For more information on traveller information systems in WA refer to the Guide for Traveller Information Displays on Variable Message Signs for Managed Freeways.
 

3.4.2 Coordinated (Route-Based) Control

 

The general “rule of thumb” for having control at a bottleneck is that you need to have control of at least six upstream ramps.  However, in practice this is variable based on a number of factors such as:
     -   Amount of flow at each upstream ramp. If any of the upstream ramps has a low flow it is not possible to build a queue and it becomes 
         ineffective as a slave. However, it also means that the low flow may not contribute much traffic to the bottleneck problem
     -   Amount of storage at each ramp. If any of the upstream ramps has poor storage it cannot provide the assistance needed as a slave in 
         holding back traffic

     -   May need more ramps to control an 8 lane freeway and less for a two lane freeway
 

Chapter 4 - Criteria for Provision of Freeway Ramp Signals


This chapter should be read in conjunction with the Main Roads document ”Managed Freeways Provision Guidelines, Part B”. 

It should be noted that, based on data from freeways in WA, there is approximately a 10% probability of flow breakdown on the freeway when the flow reaches 1,800 pc/h/ln. Since 10% probability is considered the limit of performance acceptability, the value of 1,800 pc/h/ln has been adopted in the Managed Freeways Provision Guidelines as the warrant for the provision of coordinated ramp signals. This is slightly higher than the VicRoads warrant of 1,700 pc/h/ln.
 

4.1.3 Route Treatment

 
Replace the 3rd dot point in the VicRoads Handbook with the following:
    • Where the peak period traffic volume for the freeway mainline between interchanges is 1,800 pc/h/ln or more, without flow breakdown.
 

4.1.4 Provision at New Ramps on Existing Freeways

 
Replace the 3rd dot point in the VicRoads Handbook with the following:
    • Where the peak period traffic volume for the freeway mainline between interchanges is 1,800 pc/h/ln or more, with or without flow breakdown.
 

4.2 New Freeways

    • Replace the two dot points in the VicRoads Handbook with the following:
      The peak period traffic volumes are 1,800 pc/h/ln or more for the mainline flow along any section of the new freeway,
    • The new freeway results in the downstream peak volumes between interchanges on adjacent sections of freeway to increase above a value of 1,800 pc/h/ln.
Replace Figure 4.1 and the note from the VicRoads Handbook with Figure 4.1:
  

Note:

The criteria of 1,800 pc/h/ln for provision of freeway coordinated ramp signals is based on a number of factors including:

    • The probability of flow breakdown occurring. Research by Main Roads indicates that at flows of approximately 1,700 veh/h/ln (equivalent to 1,800 pc/h/ln) there is approximately 10% probability of flow breakdown occurring (refer to Figure 4.1). At 2,000 veh/h/ln (equivalent to 2,100 pc/h/ln) the probability is in the order of 85%.
    • The objective of preventing flow breakdown, even at reasonably low levels of probability, given the economic impact that this can have on traffic efficiency and safety.
    • The breakdown at entry ramp merges is a probabilistic rather than deterministic event. Research by Elefteriadou et al (1995) demonstrates this as shown in Figure 4.2 in the VicRoads Handbook. This paper also indicates that reaching capacity flow is not a prerequisite for flow breakdown and that the clusters of vehicles from the ramp, rather than ramp flow, affect the ramp merge.
    • At mainline flows of this value, generally the entry ramp flows are also becoming significant.
    • To provide a margin for future demand increase, and
    • Consideration of traffic flows and the stability of flow on Perth’s freeways.
 
The use of pc/h/ln is due to the potential flow effects of heavy vehicles in the traffic stream.
 
Image: Figure 4.RCN-D13^23110038.GIF 
 Figure 4.1: Probability of Flow Breakdown on the Mitchell Freeway (southbound at Whitford’s Avenue entry ramp)2 
 
 

4.4 Freeway to Freeway Ramps


It should not be automatically assumed that metering of ramps upstream of freeways that join will necessarily be effective in managing the merge (as indicated in Figure 4.3). A case in point is Roe Highway joining onto Kwinana Freeway. A significant percentage of traffic heading south from Roe Highway to Kwinana Freeway originates beyond the Orrong / Welshpool interchange, where there are no opportunities to control entering traffic. Consequently, in order to control the Roe to Kwinana southbound merge, as well as other potential bottlenecks downstream (eg. the three to two lane merge at Beeliar / Armadale Road interchange) it is necessary to meter the freeway to freeway Roe to Kwinana southbound ramp.
 

4.5 Designing for Future Ramp Signals

 
The following design features should also be considered to facilitate the future retrofitting of ramp signals:
 
    • Entry ramp lengths to provide for future storage being a minimum of 420m from the ramp entrance to the ramp nose (storage for flows up to 1,200 veh/h).
    • Vehicle detector locations on the entry ramp to suit future stop line location.
    • The position and spacing of stormwater pits should be based on the future allowable spread width, assuming that the shoulder is used as a traffic lane.  If the pit spacing becomes uneconomically close, it may be necessary to allow for a nominal future shoulder width to accommodate some of the flow width.
    • Consideration should be given to using black asphalt for the shoulder, rather than red asphalt. The red asphalt should commence from the ramp entry nose.
    • Alternatively, consideration should be given to not providing a shoulder on the ramp: the ramp would be linemarked as a two-lane ramp with the “Form 1 Lane” sign and  merge in its future position. The red asphalt should commence from the ramp entry nose. If the implementation of ramp metering is likely to occur within a short timeframe (eg. the next two years or so) and it is considered undesirable to provide the pavement markings in their future position, consider using an approved temporary line marking tape, which meets Main Roads Specification 604 - avement Marking.
    • Consideration should be given to the future installation of road safety barriers to protect against crashes with the ramp signal poles. The depth and / or positions of pipes and gullies needs to be considered in relation to the depth and spacing of barrier posts.
    • Consideration should be given for verge width requirements for ramp signals and other required road side furniture, including an allowance for an appropriate pull-off area for maintenance parking.

Chapter 5 - Freeway Traffic Data

 

5.2.1 Data Station Locations

 
Details of the detector layout for a wireless data station are shown in Figure 5.2 (standard drawing no. 201231-0025).  This replaces Figure 5.2 in the VicRoads document.
 
Replace the existing dot points for items (a) and (b) as follows:
 
a) Near Entry Ramps:
    • At the end of the ramp merge, approximately 330m downstream of the nose for a single lane merge (110km/h design speed). This is the primary mainline site for ramp metering control. (For other design speeds refer to Main Roads drawing no. 201131-0021 on the website).
    • Approximately 100m upstream of the ramp nose for a typical ramp metering installation with two lanes at the stop line, with separate detectors for the ramp and mainline traffic. (Refer to Figure 5.2).
 
b) Near Exit Ramps:
    • Downstream of the exit ramp nose, with separate detectors for ramp and mainline traffic as indicated in Figure 5.2. If wireless detectors are used, the mainline detectors may be located in line with the mainline detectors for the opposing direction to facilitate communication to the access point, provided that there is a clear line of sight between the repeater and access points and provided that their distance apart is within the prescribed requirements.
 
Designers should also take into account the future position of ramp noses, particularly as a result of freeway widening
 

5.2.2 Wireless Vehicle Detectors


It should be noted that the maximum distances that detectors should be located from the access point (AP), i.e. 50m for direct transmission and 250m by relay using a battery powered repeater point (RP), should be used with caution in design, since these represent maxima under ideal operating and installation conditions. Amongst other things, the performance of wireless detectors has been found to be significantly affected by the presence of overhanging trees, or any object that interferes with the line of sight between the detectors and the AP or RP or between the AP and RP.

Details of the detector layout for a wireless or loop detector data station are shown in Figure 5.2 (standard drawing no. 201231-0025).  This replaces Figure 5.2 in the VicRoads document.
 

5.2.3 Detector Loops


Details of the loop pattern for freeway data stations are shown in Figure 5.5 (standard drawing no. 201231-0026). This replaces Figure 5.5 in the VicRoads document. 
 
Image: 201231-0025.RCN-D13^23110289.PNG 
 
 
 
Figure 5.2: Freeway Data Station using Wireless Vehicle Detectors

 
 Image: 20121-0026.RCN-D13^23110770.PNG
 
Figure 5.5: Freeway Data Station using Loop Vehicle Detectors
 
 
 
 

Chapter 6 - Design of Ramp Signal Installations

 

6.2 General Approach


The design of ramps should be carried out in accordance with Main Roads geometric design guidelines located on the internet website under Standards & Technical.
 

6.3 Capacity Analysis and Storage Design

 
Freeway and entry ramp demand flows for existing and new ramps or freeways should be based on forecast volumes obtained from the Main Roads Regional Operational Model, suitably calibrated using existing traffic data. The design flows should be based on a forecast year between 5 and 10 years after the installation of the ramp signals. 
 
Even in a suitably calibrated strategic model, one implication relating to forecast volumes is that although general volumes to/from, or on, the freeway are realistic, the volume on a specific ramp may not be precise and therefore designs may need to be flexible to allow for potential variations in volume, e.g., between adjacent entry ramps. In some cases traffic forecasts may need to be adjusted according to existing travel patterns to establish appropriate traffic flows for design. Otherwise they should be considered indicative and used for relative comparison rather than as absolute values, with suitable flexibility built into the ramp designs.
 

6.3.3 Number of Traffic Lanes at the Stop Line


As a general “rule of thumb” the number of lanes at the stop line may be obtained by dividing the ramp arrival flow by 600 and rounding up to the nearest integer. Eg. For a ramp arrival flow of 900 veh/h, the number of lanes at the stop line is given by 900/600 = 1.33, say 2 lanes.
For flows of less than 600 veh/h, consideration should also be given to storage requirements and future needs before settling on a value of 1 lane at the stop line.
Table 6.1 replaces Table 6.1 in the VicRoads document and may be used to determine the ramp storage and cycle times relative to the number of lanes at the stop line. Designs with average cycle times outside of the limits in Table 6.1 and freeway ramp metering designs which use more than 1 vehicle/green/lane (refer to the note on page 64 of the VicRoads document) shall be approved by the Manager Road Network Operations.
 
​Indicative
Layout (5)
​Ramp
 Design
Flow (veh/h)
(5) ​ ​
​Total
storage
required
(lane metres) ​ ​
​ ​Ramp Storage (3) and Cycle Time (7) relative to the number of lanes at the Stop Line  ​ ​
​ ​1 Lane ​ ​2 Lane ​ ​3 Lane ​ ​4 Lane
​Ave
storage
per lane
 (m)
​Ave
cycle time
(s)
​Ave
storage
per lane
 (m)
Ave
cycle time
(s)​
​Ave
storage
per lane
(m)
​Ave
cycle time
(s)
​Ave
storage
per lane
(m)
Ave
cycle time
 (s)​
​Single
lane
merge (6) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
 ​200 ​113 113​ 18.0​
​300 170​ 170​ 12.0​
​400 227​ 227​ 9.0​
​500 283​ 283​ 7.2 142 14.4​
​600 340​ 340​ 6.0 170​ 12.0​
​700 397​ 198​ 10.3​
​800 453​ 227​ 9.0​
​900 510​ 255​ 8.0​ 170​ 12.0​
​1000 567​ 283​ 7.2 189​ 10.8​
​1100 623​ 312​ 6.5 208​ 9.8​
​1200 680​ 340​ 6.0 227​ 9.0​
​Added
lane
entering
the
freeway
or
Two lane
merge
​ ​ ​ ​
​1300 737​ 246​ 8.3​ 184​ 11.1​
​1400 793​ 264​ 7.7​ 198​ 10.3​
​1500 850​ 283​ 7.2​ 213​ 9.6​
​1600 907​ 302​ 6.8​ 227​ 9.0​
​1700 963​ 321​ 6.4 241​ 8.5​
​1800 1020​ 340​ 6.0 255​ 8.0​

​​Added
lane
entering
the
freeway
plus
a
merging
lane ​ ​ ​

 

​ ​ ​ ​ ​ ​ ​
​1900 1077​ 269​ 7.6​
​2000 1133​ 283​ 7.2​
​2100 1190​ 298​ 6.9​
​2200 1247​ 312​ 6.5​
2300 ​1303 ​326 6.3
2400​ 1360​ 240​ 6.0
2500​ 1417​ 354​ 5.8
2600​ 1473​ 368​ 5.5
2700​ 1530​ 383​ 5.3
2800​ 1587​ 397​ 5.1
2900​ 1643​ 411​ 5.0
3000​ 1700​ 425​ 4.8

Notes:

  1. Maximum wait per vehicle (min.) : 4
  2. Storage per vehicle (m) : 8.5
  3. Average storage per lane assumes lanes of equal length. Not applicable with auxiliary lanes at the stop line.
  4. No. of vehicles / green / lane : 1
  5. Ramp layout and ramp design flow are subject to the bottleneck capacity on the mainline (refer VicRoads document Section 6.2.2)
  6. A single lane merge layout may be satisfactory for higher flows, e.g. a ramp flow of 1600 veh/h with a mainline of 2400 veh/h on a two-lane freeway mainline (i.e. combined flow < 2000 veh/h/ln.)
  7. Cycle times lower than values in black are generally not appropriate as an average cycle over the design hour. Cycle times in red may be appropriate at ramps with spare mainline merge capacity (refer VicRoads document Section 6.2.3).
  8. Designs with average cycle times outside the limits in this table shall be approved by the Manager Road Network Operations.
 
 
Table 6.1: Lanes at the Stop Line and Ramp Storage Requirements
           
 

6.3.4 Ramp Storage Requirements

 

6.3.4.1 Desirable Standard

 
The desirable standard is to provide for a total length of storage between the stop line and the ramp entrance to accommodate traffic with a wait time of 4 minutes, i.e. the ramp queue delay. This shall be applied for all new freeway ramps and is applicable to the values in Table 6.1.
 

6.3.4.2 Storage Difficulties


In retrofit situations where providing the desirable storage is not achievable and where there is no possibility of extending the nose, a lower storage value may be adopted, provided the analysis indicates that entry ramp demands are satisfied and provided that measures to accommodate ramp overflow onto the arterial roads have been considered (VicRoads document Section 6.3.5). Moreover, other upstream ramps (and downstream ramps when considering the critical bottleneck) should be provided with more than the desirable standard to compensate for the loss of overall system storage. 

In a situation where at an individual ramp the desirable storage cannot be achieved, an absolute minimum of 3 minutes storage shall be provided. The average storage for all ramps used to control the critical bottleneck should be greater than 4 minutes.

The adoption of the minimum 95th percentile queue length for design purposes shall not be used in WA. Equations 6-4 to 6-7 are not be used.
 

6.3.4.3 Example of Capacity and Storage Calculations

 
An Excel spreadsheet to calculate capacity and storage requirements along a route may be downloaded here.
 

6.4 Geometric Design and Layout of Devices

 

6.4.1 General Ramp Layout


The layouts in the standard drawings are based on the geometric standards for freeway entry ramps in the WA road design guidelines.  Standard ramp layout drawings are given in the “Guideline Drawings” under ”Grade Separated Interchanges”.
 
 

6.4.1.2 Standard Drawings

Table 6.2 replaces Table 6.2 in the VicRoads document:

Ramp Type

Drawing No.

Two lanes of metered traffic

 201231-0027

Two lanes of metered traffic plus a free flow priority lane

 201231-0028

Two lanes of metered traffic plus a metered priority lane

 201231-0029

Three lanes of metered traffic to one lane at the nose

 201231-0030

Four lanes of metered traffic to two lanes at the nose

 201231-0031

Three lanes of metered traffic to two lanes at the nose

 201231-0032

Freeway to freeway interchange

201231-0053

 

  Table 6.2: Standard Drawings for Freeway Ramp Signals

 
 
 

6.4.2 Two Lane Entry Ramp (Dwg. No. 201231-0027)

 
The typical entry ramp layout for a ramp with two metered lanes is shown in Figure 6.6 over the page.  This replaces Figure 6.6 in the VicRoads document.
 
For two lane ramps, the stop line is located a desirable minimum distance of 100m upstream of the ramp nose. In retrofit situations where ramp storage is an issue, an absolute minimum of 80m may be used subject to approval from the Manager Road & Traffic Engineering.  Specific site conditions where the distance from the stop line to the nose may need to be increased should be considered as per the VicRoads document.
 
Image: 201231-0027.RCN-D13^23113108.PNG 
Figure 6.6: Typical Freeway Ramp Signals Layout - 2 Metered Lanes
 

6.4.3 Priority Access Lanes

 
Priority access lanes shall be provided in accordance with the Main Roads document “Provision Guidelines for Managed Freeways, Part B”.
 
With appropriate regulatory signing as outlined in Section 6.4.13 (eg. “Truck lane” signs), a priority lane is enforceable under the Road Traffic Code 2000 (Regulations 133, 134, 135 & 136).
 

6.4.3.1 Freeflow Priority lane (Drawing No. 201231-0028)


Free flow bypass lanes provide an uncontrolled movement of priority vehicles along the ramp and avoid the need for vehicles to stop.  However, the uncontrolled entry flow can cause problems for management of the mainline when there are heavy freeway demands.  Therefore, uncontrolled free flow bypass lanes should be carefully considered when detailed analysis has shown there are critical bottlenecks within three to four downstream sections of the motorway. The location of other free flow priority lanes may also need to be considered to ensure that adequate control of mainline flow can be achieved.
Drawing No. 201231-0028 shall be used when a freeflow priority lane is to be provided with or without a downstream added lane

The entry ramp layout for a ramp with a freeflow by-pass lane is shown in Figure 6.8. This replaces Figure 6.8 in the VicRoads document. The geometry is based on the following design principles (assuming a flat grade):
    • The stop line is 100m (desirable distance) or 80m (absolute minimum in constrained retrofit situations and subject to the approval of the Manager Road & Traffic Engineering) from the ramp nose for the two vehicles leaving the stop line to merge.
    • A painted median (0.7m wide with 500mm wide diagonals at 45o  and at 10m spacing) is provided between the bypass lane and the metered vehicle lane. This separation tapers to a single 150mm wide continuous lane line over the 100m merge distance.
    • The distance from the nose to the start of the bypass merge taper is similar to the standard merge length from the nose to the end of the merge taper (Dwg No. 201131-0021 on the website). This distance allows vehicles to merge with the freeway traffic or choose to stay in the auxiliary lane and allow by-pass vehicles to merge.  This distance should be based on the acceleration requirements of either (a) a heavy vehicle passing the stop line at a speed appropriate to the ramp geometry, or (b) a light vehicle accelerating from a stopped position.  In either case the desired operating speed is 80km/h.\The bypass lane merge taper is the standard freeway merge length based on a lateral velocity of 0.6m/s. For a design speed of 110km/h this equates to approximately 175m.
    • The 100m parallel auxiliary lane is based on 4 seconds travel at 100km/h.  Where downstream obstructions restrict the available length, this parallel section may be reduced, if justified.
    • The final merge taper is the standard freeway merge length based on a lateral velocity of 0.6m/s. For a design speed of 110km/h this equates to approximately 175m. Kerb and channel is provided over the total distance available for the merging movements downstream of the ramp nose to minimise formation width, i.e. with no shoulder. The shoulder develops over the final merge taper to match into the existing freeway shoulder.
 
For ramp signal layouts with more than two general traffic lanes in addition to a freeflow priority lane, the merge distances shown in Figures 6.10 and 6.11 of this document (replacing the VicRoads figures) should be used in conjunction with the design principles given above to justify the design.  In addition, merge and acceleration distances should be adjusted for any uphill grades.
 
Image: 201231-0028.RCN-D13^23113626.PNG 
Figure 6.8: Typical Freeway Ramp Signals Layout – Free Flow Priority Lane

 

6.4.3.2 Metered Priority lane (Figure 6.9 - Dwg. No. 201231-0029)

 
The typical entry ramp layout for a ramp with a metered by-pass lane is shown in Figure 6.9.  This replaces Figure 6.9 in the VicRoads document.  The geometry is based on the following design principles (assuming a flat grade):
 
    • The stop line is 160 - 180m from the nose, allowing 80m (absolute minimum) - 100m (desirable minimum) for the two vehicles leaving the stop line to merge and then a further 80m to merge with the bypass lane traffic. The absolute minimum may only be applied in retrofit situations with space constraints and then only with the approval of the Manager Road & Traffic Engineering.  If the bypass lane is a priority truck lane, then it would be expected that the two light vehicles will be well in front at this point.
    • The distance of from the nose to the end of the gore marking is consistent with the standard merge length from the nose to the end of the gore marking (edges meet point - refer Dwg No. 201131-0021 on the webThe parallel auxiliary lane allows for a minimum of 4 seconds of travel at an operating speed of 100km/h. This distance may be increased up to 200m (Refer to Table 11.4 in Austroads Guide to Road Design Part 4C) to allow for acceleration distance for heavy vehicles. Within this section vehicles may choose to change lanes to merge with the freeway traffic or stay in the auxiliary lane and merge downstream.
    • The merge taper is the standard freeway merge length based on a lateral velocity of 0.6m/s. For a design speed of 110km/h this equates to approximately 175m
    • The shoulder develops over the last 80m before the nose (merge between bypass lane and general traffic) to match into the existing freeway shoulder. This acts as a “run-out” area and provides additional width for safety in the event that merging manoeuvres are not completed by the nose.
A disadvantage of the metered bypass layout is the reduced storage on the ramp compared with a setback of 100m from the stop line with no priority lane, unless the ramp is lengthened by extending the nose.  On the other hand, the distance required to merge the traffic on the mainline is less.
 
For ramp signal layouts with more than two general traffic lanes in addition to a metered priority lane, the merge distances shown in Figures 6.10 and 6.11 of this document (replacing the VicRoads figures) should be used in conjunction with the design principles given above to justify the design. In addition, merge and acceleration distances should be adjusted for any uphill grades.
 
Image: 201231-0029.RCN-D13^23113622.PNG 
Figure 6.9: Typical Freeway ramp Signals layout – Metered Priority Lane
 
 

6.4.4 Three and Four Lanes at the Stop Line (Dwg. Nos. 201231-0030, 201231-0031 and 201231-0032)

 
The typical entry layouts for ramps with three metered lanes and four metered lanes (without priority bypass lanes) are shown in Figures 6.10, 6.10(b) and 6.11. These replace Figures 6.10 and 6.11 in the VicRoads document.
 
Figure 6.10(a) below is a special case alternative to the layouts for ramps with three metered lanes. The layout consists of three metered lanes merging to one over a distance of 100m. The use of the continuity line and the stop line set back of 3m for the left-hand lane ensures that the vehicle in the left-hand lane merges behind the other two vehicles. This layout shall only be used in the following circumstances:
 
    • The option of merging two lanes together first (over 80m) and then merging with the third lane (over 100m desirable, 80m minimum) as shown in Figure 6.10 (Drawing no. 201231-0030) is not possible due to storage constraints.
    • The third lane must be developed at the stop line using a localised flaring layout.
    • Approval for use of this layout should be obtained from the Manager Road & Traffic Engineering. 

 

Image: Figure 6.RCN-D13^23115065.PNG 
Figure 6.10(a): Freeway Ramp Signals layout - 3 Metered Lanes - Special Case
 
 
 
Image: 201231-0030.RCN-D13^23113636.PNG 
Figure 6.10: Typical Freeway Ramp Signals Layout - 3 Metered Lanes to 1 at the Nose
 
 
Image: 201231-0032.RCN-D13^23113642.PNG 
Figure 6.10(b): Typical Freeway Ramp Signals Layout - 3 Metered Lanes to 2 at the Nose
 

 

Image: 201231-0031.RCN-D13^23113641.PNG
Figure 6.11: Typical Freeway Ramp Signals Layout - 4 Metered Lanes to 2 at the Nose
 
 
 

6.4.5 Freeway to Freeway Ramp Metering (Dwg. No. 201231-0053) 

 
A typical layout for the freeway ramp signals is shown in Figure 6.12 (Standard Dwg. No. 201231-0053) for situations where freeway to freeway entry ramps are to be metered. This figure replaces Figure 6.12 in the VicRoads document and is given over the page.
 

6.4.6 Controller (Cabinet) Location

 
A controller location between the ramp and the freeway carriageway is generally undesirable unless the controller can be located at the start of the ramp where good visibility to the signals and the freeway beyond is provided. An advantage of this location is that, where the arterial road passes over the freeway, the area is usually protected by a safety barrier. It is important that there is sufficient space to park on the left hand side of the ramp or left-turn splitter island.
 

6.4.7 Signal Pedestals (Posts)

 
In WA “signal pedestals” or “signal support pedestals” are called “signal posts”.
 
The signal post is installed adjacent to the ramp 10m downstream of the stop line. The standard for 2 lane ramps is a modified mast arm with an outreach of 5.5m and a footing depth of 2.4m. This is shown in Figure 6.12(a) (Standard Dwg. No. 1230-2499).  The use of joint use mast arms (JUMA) to mount a CCTV camera is not supported in WA since all CCTV installations require a scissor-type accessible extension, rather than access through the use of a mobile platform.  However, where wireless vehicle detectors are used, a mast arm extension may be needed for mounting of the RP (refer Figure 5.2) if a lighting pole is not available.
 
Gantries are required for ramps with 3 or 4 lanes including installations with priority access lanes. Generally, the clearance to the underside of the lowest fixture on the structure shall be 6.0m on ramps leading to the Kwinana or Mitchell Freeways, or 7.0m on ramps leading to Roe Highway.  This should be confirmed on a case-by-case basis with the Structures Branch and the Heavy Vehicle Operations Branch.
 
As the traffic signal mast arms and gantry supports are considered non frangible roadside hazards, the installation shall include a safety barrier.  For the gantry leg on the right side of the ramp, a safety barrier may be necessary to shield the hazard from mainline traffic as well ramp traffic. The requirements of MRWA Supplement to Austroads Guide to Road Design - Part 6 and Austroads Guide to Road Design - Part 6: Roadside Design, Safety and Barriers must be met at all locations.
 
In positioning the signal mast arms, appropriate allowances should be made for the deflection of the barrier, vehicle roll and the width of the signal lanterns and their target boards. As a general guide the following deflection distances should be adhered to:
    • Concrete barrier - no deflection (allow width of the barrier and vehicle roll allowance)
    • W-Beam - 1.5m from the face of the barrier
    • Wire rope barrier - 2.0m from the face of the barrier 

Image: 201231-0053.RCN-D13^23113630.PNG 

Figure 6.12: Typical Freeway Ramp Signals Layout – Freeway to Freeway Ramps

 
 
 
 
 Image: 1230-2499.RCN-D13^23113643.PNG 
Figure 6.12(a): Traffic Signal Mast for Ramp Signals – 5.5m Outreach: General Arrangement & Details
 
  
 

6.4.8 Signal Lanterns


The high mount lanterns are considered the primary lanterns and should be aimed towards the ramp entrance at a distance of 170m. This is based on an assumed ramp speed of 80km/h. 

Where traffic signals are installed on standard 5.5m outreach mast arms (modified for ramp signal installations), the overhead (primary) lanterns shall be mounted at a minimum height of 5.8m (measured from the ground to the bottom of the target board). 

Where traffic signals are installed on overhead gantries, the primary lanterns shall be mounted at a height of 6.0m on ramps leading to the Kwinana or Mitchell Freeways, or 7.0m on ramps leading to Roe Highway (measured from the ground to the bottom of the target board). This should be confirmed on a case-by-case basis with the Structures Branch and the Heavy Vehicle Operations Branch.

The low mount lanterns are considered the secondary lanterns and should be aimed at a point on the centre of the ramp approach, 3m upstream of the stop line. The lower lantern is to be mounted at a height of 2.2m (measured from the ground to the bottom of the target board). 
 
 

6.4.10.3 Ramp Entrance Detectors

 
For a ramp that is longer than the desirable storage from the stop line the ‘ramp entrance’ detectors are placed at the 4 minute queue distance.
In WA consideration will not be given to providing detectors at a distance of 0.75 x desirable storage, i.e. 3 minutes access time. 
 
 

6.4.12.1 RC1 Warning and Regulatory Sign (Electronic)

 
The RC1 signs (Ramp Signals On) are installed on the approaches to the arterial road / entry ramp intersection to face traffic turning into the ramp.  They are generally installed in the following positions, as illustrated in Figure 6.13(a):
    • For traffic approaching the on-ramp and turning left into the on-ramp - on the left-hand primary traffic signal post located in the left-turn splitter island if the sign will be within the line of sight for left turning motorists.  For large traffic islands a separate post may be necessary.
    • For traffic approaching the on-ramp and turning right into the on-ramp - on the right-hand secondary traffic signal post located in the median.
 
 Image: Figure 6.RCN-D13^23114684.PNG
 
Figure 6.13: RC1 Sign Messages
 
 
 
 
Image: Figure 6.RCN-D13^23114683.PNG 
Figure 6.13(a): Typical Location of RC1 Signs
 
 
 

6.4.12.3 RC3 Sign – Real Time Information Sign (Electronic)

 
 
Joint use signal poles (JUP) are not used in WA.
 
 

6.4.13 Other Signs


Static signs shown on the drawings as forming part of the ramp signals installation include:
  • STOP HERE ON RED SIGNAL (R6-6B)

    These regulatory signs are required at the stop line as it is remote from the traffic signals (generally 10m upstream).

Image: R6-6B.RCN-D13^23110173.PNG 

  • ​ONE VEHICLE PER GREEN EACH LANE (MR-GT-23)

    These signs are located underneath the low mount lantern (at a mounting height of 1.5m to the underside of the sign) and mid-way between the overhead lanterns.

Image: MR-GT-23.RCN-D13^23110179.GIF

  • FORM 1 LANE (G9-15B)

    These signs are located each side of the ramp 20m downstream of the stop line. Where the merging from the stop line on 3 or 4 lane ramps is to form two lanes at the ramp nose, FORM 2 LANES signs (G9-16B) shall be used.


Image: G9-15B.RCN-D13^23110175.PNG 

  • ​Speed Limit sign (R4-1C) or variable speed limit sign, together with “START OF FREEWAY” (MR-GE-22B) sign.
These signs are located 30m downstream of the last “FORM 1 LANE” or “FORM 2 LANES” signs before the ramp nose.

Image: R4-1C.RCN-D13^23110172.PNG

Image: MR-GE-22B.RCN-D13^23110176.PNG 

  • Truck lane signs (R7-3-1) to designate the use of the left lane if a priority bypass lane is provided. The use and positioning of these signs is consistent with regulation 135 of the Road Traffic Code 2000. The signs are supplemented with a “LEFT LANE” (R7-3) or “SIGNALS DO NOT APPLY” (MR-GT-24) sign as appropriate.

    Note: If classes of vehicle other than trucks, or in addition to trucks, are permitted to use the priority bypass lane then the sign must reflect the appropriate vehicle classes.

Image: R7-3-1.RCN-D13^23110178.PNG       Image: MR-GT-24.RCN-D13^23110177.PNG

Image: R7-3.RCN-D13^23110170.PNG 

 

 

6.4.14 Pavement Markings 

 
The pavement markings and RRPMs associated with the ramp signal designs as shown on the standard drawings given in Table 6.2 are consistent with the “Pavement Marking” standard drawings provided on the Main Roads website and the following principles:
    • Longitudinal line marking includes a 25m single continuous lane line (150mm wide) on the approach to the stop line with 5 no. white unidirectional RRPM’s on the right hand side at 6m spacing. 
    • A 150mm wide edge line is provided on the left hand side of the ramp, starting at the stop line to provide guidance for the merging traffic. On the right hand side the 150mm wide edge line starts approximately 12m from the nose in accordance with standard Dwg. No. 200331-093 on the website.
    • The stop line is located 10m upstream of the traffic signal pedestal.
    • A continuous lane line, or painted median, should always be installed between two lanes merging and any other lane to “discourage” lane changing into an area where merging may take place.
    • All merging manoeuvres occur as a “zip” merge, i.e. no continuity line is used.
    • The gore markings continue to a point, rather than terminating where the painted median is 1.2m wide (refer to Figure 6.16 and standard Dwg. no. 200331-093).
    • At the end of the merge taper where the edge line of the ramp joins with the freeway edge line (“edges meet” point), the 150mm wide edge line should be marked as a clearly defined angle, rather than as a smoothed curve (refer to Figure 6.16).
    • The entry taper to a priority vehicle bypass lane shall be highlighted using appropriate pavement marking messages in accordance with AS1742.12 - Bus, transit, tram and truck lanes. This is illustrated in Figure 6.17 (Standard Dwg. No. 201231-0021).
    • Where a priority vehicle bypass lane is provided, the bypass lane shall be separated from the general traffic lanes by a painted median 0.7m wide. The painted median shall have 150mm wide edgelines with 0.5m wide painted diagonals at 45 degrees at 10m spacing as well as yellow rumble bars at 5m spacing. This is supplemented with groups of 4 no. yellow unidirectional RRPM’s, also aligned at 45o. This is illustrated in Detail A of Figure 6.17 (Standard Dwg. No. 201231-0021).

 

Image: Figure 6.RCN-D13^23110209.PNG 

Figure 6.16: Line Marking at the “Edges Meet” Point 

 

 

 Image: 201231-0021.RCN-D13^23115225.PNG

 Figure 6.17: Freeflow Truck Bypass Lane – Indicative Signs and Line Marking

 

  

6.4.16 Conduits (Power Supply)


The power supply connection to the ramp signal controller is provided either from an existing Main Roads point of supply or a new Western Power point of supply.  Power is then distributed to other devices. For RC3 signs (Real Time Traveller Information sign) where wireless communications are provided to the signs, a separate local power supply may be provided by Western Power or power may be obtained from a nearby Main Roads street light pole.
 

6.4.17 Lighting


Street lighting is required on all ramps as per Main Roads Roadway Lighting Guidelines.
 
 

Chapter 7 – Operation of Ramp Signals

 

7.1 Legal Basis for Ramp Signals

 
Freeway ramp signals are traffic lights as defined in the Road Traffic Code 2000.  Regulation nos. 39, 40 and 41 defines a driver’s responsibilities when approaching, or at, a green, red or yellow traffic light. Other rules define responsibilities relating to the stop line and other regulatory signs and pavement markings associated with freeway ramp signals.
 
A traffic-control signal is defined in the Road Traffic Code 2000.  The Executive Director Road Network Services of Main Roads must give approval to erect, establish, display, maintain or remove freeway ramp signals.
 

7.2 Control algorithms used by Main Roads

 
Main Roads proposes to use the same suite of algorithms as VicRoads.