MCH 2474 Ramp Metering Operational Procedures

Transcription

1 MCH 2474 Issue B March 2008 MCH 2474 Ramp Metering Crown Copyright 2008 First published 2008 Printed and published by the Highways Agency

2 Ramp Metering DOCUMENT REF: MCH 2474 B MCH 2474 with amendements Rob Porter Dave Hunter Babar Malik Julian Steed 17/03/08 A Reissued as MCH 2474 Rob Porter Alan Hindley Babar Malik Julian Steed 25/02/08 03 Initial Issue Rob Porter Alan Hindley Babar Malik Julian Steed 05/12/07 02 Draft for client approval Rob Porter Alan Hindley Babar Malik Julian Steed 30/11/07 01 Draft for client comment Rob Porter Alan Hindley Peter Kirby Julian Steed 29/11/07 Originated Checked Reviewed Authorised Date Revision Purpose Description

3 Contents Section Executive Summary Page ii 1. Introduction Ramp Metering Deployment System Functionality System Stakeholders Document Distribution Related Documents Operational Requirements Operation and Maintenance Stakeholders Traffic Management Considerations System Shutdown 2-8 Appendix A Note for Shutting down a Ramp Metering System A-9 Appendix B Traffic Management Considerations B-16 List of Tables Table List of Access Levels 1-2 Table List of Related Documents 1-4 Table Possible Scenarios 2-8 List of Figures Figure Scheme Life Cycle 1-5 Figure A.1 - Switch Off Process Steps 1 to 6 A-12 Figure A.2 - Switch Off Process - Steps 7 to 8 A-13 Figure A.3 - Switch Off Process - Steps 9 to 14 A-14 Figure A.4 - Switch Off Process - Steps 15 to 18 A-15 Figure B.1 - The Ramp Metering Vicinity B-16 Figure B.2 - Dealing with TM in the Ramp Metering Vicinity B-17 March 2008 i MCH 2474

4 Executive Summary The Highways Agency undertook a project to deliver 30 ramp metering systems by the end of March These systems are intended to increase the traffic flow capacity of existing motorway junctions by regulating the slip road traffic flows. This document provides the necessary first line operational procedures to ensure safe and efficient operation of the system. Whilst this document is aimed at the operational requirements of the 30 initial ramp metering sites, it is also intended to form the basis for future ramp metering installations. March 2008 ii MCH 2474

5 1. Introduction 1.1 Ramp Metering Deployment The Highways Agency undertook a project to deliver 30 ramp metering systems by the end of March The ramp metering systems are located in the West Midlands and the North of England. The 30 sites have been installed in the following Highways Agency Areas. Area 9 (West Midlands) Area 10 (NW England) Area 11 (West Midlands) Area 12 (Yorkshire) 1.2 System Functionality The ramp metering system is stand alone and does not require any operator intervention during normal operation. If the flows in the vicinity of the ramp metering site change considerably due to traffic management, the system may require turning off temporarily. The systems are calibrated specifically for the worst case traffic scenario and will adjust their operation to provide benefits across changing and seasonal conditions. The system remains in standby mode and constantly monitors the traffic conditions until the mainline approaches flow breakdown. At this time, if the upstream lane one speed is below the safe operating speed and the downstream occupancy is above the switch on threshold then the system will automatically start up and regulate the flow of traffic onto the main carriageway. Ramp metering reacts to changing mainline traffic conditions and changes the signal timings to control flow rate released from the slip road. Regulating this flow helps to delay, or stop the occurrence of, flow breakdown and also aids flow recovery. During normal operation the system will form a queue on the slip road and this storage of vehicles is vital for the operation of ramp metering. However the slip road queue is managed to reduce any unnecessary delays and prevent traffic queuing onto the local road network. Provisions have been made for remote monitoring and maintenance of the ramp metering system via the Internet. Each site has an individual website address. Usernames and passwords will be required to access the sites. Two access levels are currently available, read only and read and write. Using the remote internet access with the correct access level will enable the user to turn the site on or off, configure the various parameters and download data and fault logs. A typical Ramp Metering site has 10 configurable users with site specific usernames and passwords. For security reasons the write passwords for the ramp metering system are not written here but will be provided to each user as part of the handover process. March MCH 2474

6 Table 1.1 shows the current access levels allocated to the stakeholders for the Area 10 sites; this convention is used across all areas. User Name Description Status Comments nwrccview A10 RCC Monitor Read Only Area 10, RCC read only nwrccadmin A10 RCC Admin Read and Write Area 10, RCC read and write a10rmcview A10 RMC Monitor Read Only a10rmcadmin A10 RMC Admin Read and Write Area 10, Primary Maintainer read only Area 10, Primary Maintainer read and write hagenview HA Gen. Monitor Read Only HA read only ahgenadmin HA Gen. Admin Read and Write HA read and write atkinsview Atkins Monitor Read Only Atkins read only atkinsadmin Atkins Admin Read and Write Atkins read and write ipladmin IPL Admin Read and Write IPL read and write peekadmin Peek Admin Read and Write Peek read and write Table List of Access Levels March MCH 2474

7 1.3 System Stakeholders There are several stakeholders involved with the ramp metering systems. The level of involvement of each party varies and covers a range of aspects such as site selection, design, construction and calibration. Whilst all these aspects are not core to the operational regime, it is important to ensure that all stakeholders are aware of the roles and responsibilities of the various parties. The system stakeholders include but are not limited to: Highways Agency TechMAC & MAC / SuperMAC (Primary Maintainers) System Suppliers (IPL/Peek, etc) National Roads Telecommunications Service (NRTS) Ramp Metering Task Force A detailed description of the responsibilities of each system stakeholder can be found in the Ramp Metering Fault Management and Maintenance Procedures document (reference MCH 2475). 1.4 Document Distribution This document is to be distributed and agreed by all the system stakeholders who are as follows: Highways Agency SSR Highways Agency TO (on a national level) TechMAC (or SuperMAC) MAC (or SuperMAC) System Supplier (IPL/Peek) March MCH 2474

8 1.5 Related Documents Table 1.2 below lists the documents related to the design, installation, operation and maintenance of a Ramp Metering site. Figure 1.1 below gives and overview of the Ramp Metering scheme life cycle. Reference MCH1965 IAN 103/08 MCH 2470 Document Title Ramp Metering System Requirements Specification Advice Regarding the Assessment of Sites for Ramp Metering Ramp Metering Technical Design Guidelines MCH 2471 Ramp Metering Installation Guidelines MCH 2472 Ramp Metering Configuration Setup and Management MCH 2473 Ramp Metering Calibration Guidelines MCH 2474 Ramp Metering MCH 2475 Ramp Metering Maintenance Handover Procedures _04_02_027 Ramp Metering Operational Assessment Table List of Related Documents March MCH 2474

9 Site Selection IAN 103/08 Advice Regarding the Assessment of Sites for Ramp Metering Operational Strategy MCH 2470 Ramp Metering Technical Design Guidelines Design MCH 2470 Ramp Metering Technical Design Guidelines Configuration Setup MCH 2472 Ramp Metering Configuration Setup and Management Guidelines Infrastructure Installation and Test MCH 2471 Ramp Metering Installation Guidelines System Installation and Commissioning System Procurement and Supply MCH 1965 Calibration MCH 2473 Ramp Metering Calibration Guidelines Configuration Management MCH 2472 Ramp Metering Configuration Setup and Management Guidelines Operation and Maintenance MCH 2475 Ramp Metering Maintenance Handover Procedures MCH 2474 Ramp Metering Operational Procedures Evaluation _04_02_027 Ramp Metering Operational Assessment Report Figure 1.1 Ramp Metering Scheme Life Cycle March MCH 2474

10 2. Operational Requirements As described in section 1.3, the ramp metering system is a stand alone system and requires minimal operator intervention. The most likely operational requirement will be to deactivate the system during an incident on the motorway network or when traffic management (TM) is deployed on the slip road. This is described in detail in sections 2.2 and Operation and Maintenance Stakeholders Below is a brief description of each of the stakeholders involved in the operation and maintenance of a ramp metering site. The operational responsibilities are described here and a more detailed description of the maintenance responsibilities of each party can be found in the Ramp Metering Fault Management and Maintenance Procedures document (reference MCH 2475). Safety Standards and Research, Highways Agency (SSR) SSR do not have any direct operational responsibilities for the ramp metering systems. SSR has been responsible for determining operation and maintenance procedures and will remain available to offer advice on any arising issues. Traffic Operations, Highways Agency (TO) The Local TO Area is responsible for ensuring that the ramp metering systems offer benefits to the motorists and the local area. This top-level responsibility is merely an extension to the Area s current regime of ensuring best-network performance. The RCC operators with the knowledge of the local network and incidents are to advise if and when the sites are to be deactivated. This is described further in section 2.3 in conjunction with a list of possible scenarios. Appendix A details the procedure for safely shutting down a ramp metering system. Managing Agents, TechMAC & MAC (Primary Maintainers) The TechMAC as the primary maintainer are responsible for the operational availability of the ramp metering systems. The TechMAC will be responsible for the rectification of any faults within the timescales set in the Ramp Metering Fault Management and Maintenance Procedures document (reference MCH 2475). The primary maintainer will also be responsible for the safe activation and deactivation of ramp metering sites as advised by RCC operators. MAC (or MA & TMC) The MAC will also be responsible for ensuring that any future works on the network consider the location and operation of any local ramp metering systems and the network assets on which the ramp metering system relies. It is anticipated that March MCH 2474

11 measures are to be put in place to take ramp metering systems into account during the road space booking procedure. Further information and guidance on these issues can be found in Section 2.2 and Appendix B. System Supplier (IPL/Peek) (As advised by the TechMAC) IPL/ Peek will be responsible for the system aspects as supplied and installed by them. This requirement falls under IPL/ Peek s existing contract with the Highways Agency which runs until June NRTS NRTS will be responsible for the maintenance of all communication aspects of the Ramp Metering systems. NRTS have no operational responsibilities. Ramp Metering Task Force The Ramp Metering Task Force is to provide technical support to the primary maintainers to ensure the operational effectiveness of the systems. This will take the form of systematic review of sites to maximise benefits, facilitate training courses, support during commissioning and calibration. 2.2 Traffic Management Considerations Early experience from one of the 30 sites highlighted a threat to the network s operation if the appropriate procedures are not undertaken when deploying traffic management in the vicinity of a ramp metering system. In this particular example, the road space booking process did not consider the ramp metering system operation. The resultant lane two closure of the slip road caused the ramp metering system to release only half the vehicles from the stopline that the algorithm had calculated were required. This low flow from the stopline created considerable congestion on the local authority roads. The congestion problem was compounded by the system algorithms calculating that the occupancy of the slip road, and therefore the length of queue, was only half the true value. If traffic management is deployed on the mainline that results in vehicles running in a reduced number of lanes or the hard shoulder, the measured occupancy at the downstream site will not reflect the true conditions. This will lead to the ramp metering signals delivering an inappropriate amount of traffic for that particular condition. Appendix B provides an overview of how the ramp metering system relies on and interacts with the local environment. Following this overview, advice is given for traffic management and road space booking procedures to avoid similar operational problems in the future. Appendix A details the steps required to switch the ramp metering systems on and off and should be read in conjunction with Appendix B March MCH 2474

12 2.3 System Shutdown A system shutdown would be required when an incident occurs on the network which affects how the ramp metering system reacts to traffic conditions. If a vehicle was broken down in or around the merge area, there is a high chance that the normal operation of the ramp metering system will be unsuitable until the incident has cleared. The ramp metering system should be switched off in these circumstances. In the event of such an incident, it will be clear on-street if the system needs to be switched off. See table 2.1 below for a list of possible scenarios and actions. Scenarios Action Comments Unusually high slip road traffic (transitory rather than a long term change of traffic patterns). Unusually high main carriageway traffic (transitory rather than a long term change of traffic patterns). Special event in the locality changes traffic patterns. None. None. None assuming the system is enabled to come on at any time of the day/week. System will adjust its operation accordingly and the queue management and queue override functions will protect the local roads. System will adjust its operation accordingly and delay flow breakdown and aid mainline recovery. If set for peak periods only then benefit could be obtained by turning the system on to deal with any special event traffic. Accident on the main carriageway upstream of the metered junction. None. System will adjust its operation according to the resulting downstream conditions. Accident on the main carriageway downstream of the metered junction. None. Traffic may be heavier or may come to a standstill at the junction. In either case the system will adjust its operation accordingly and will benefit the approach to and recovery from flow breakdown. Accident on the main carriageway between the merge and the downstream MIDAS detection point. Accident on the slip road upstream of the RM signals. Accident on the slip road downstream of the RM signals. Traffic management lane closure on main carriageway or slip road. Traffic management hard shoulder closure on main carriageway or slip road. If unusual performance is observed the systems should be turned off temporarily. If unusual performance is observed the system should be turned off temporarily. It may also be prudent to turn the system off if slip road queuing is likely to hinder access or activities of the emergency services or add to excessive queuing on local roads. It may also be prudent to turn the system off if slip road queuing is likely to hinder access for the emergency services. If unusual performance is observed the systems should be turned off for the duration of the traffic management. None. In unusual circumstances an accident could result in erroneous inputs to the system. Likely effect is an inappropriate metering rate, too high or too low. It is highly unlikely, but possible, that the system could turn on at an inappropriate main carriageway speed, increasing the risk of further accidents. Note: if the system is manually turned off there may be some delay before the signals heads switch off. An accident on the slip road is likely to result in erroneous inputs to the system and an inappropriate metering rate. Slip road queuing may hinder access for the emergency services. If active at the time, ramp metering may have the beneficial effect of slowing traffic on the approach to the accident, but slip road queuing may hinder access for the emergency services. Depending on the exact location of the traffic management this could result in erroneous inputs to the system and an inappropriate metering rate. Ramp Metering Task Force to be consulted where long term traffic management is to be installed. System does not read data from any hard shoulder location so operation should continue as normal Severe weather conditions Turn off temporarily if risk of accidents is increased. System should cope with most weather variations. Network changes, e.g. widening of a section of motorway or new junction added. No operational action but calibration review should be undertaken. System will adjust to some extent, but calibration review should be organised. Ramp Metering Task Force to be consulted to evaluate the need for re-calibration. Unable to communicate with the ramp metering system. Request communications check and reset It is possible for the communications to fail whist the rest of the system continues as normal. This should be investigated and resolved so that communications is available to deal with incidents in the future. Malfunction of the ramp metering system. Request roadside isolation. Table Possible Scenarios Most failures cause the system to turn itself off immediately. In very rare circumstances it is possible that the system could malfunction and not respond to the communications link. In these circumstances the signal heads can be isolated from the controller (i.e. the heads are electrically turned off). Attendance at site is required. Whilst theoretically possible, this failure mode has not occurred to date. March MCH 2474

13 Appendix A Note for Shutting down a Ramp Metering System In certain circumstances it is necessary to switch off a ramp metering system at a particular junction. This is achieved by accessing the Supervisory Interface for that junction by using a login with the correct access level privileges. Once access to the site has been gained, the site activationmode within the SwitchOnOff algorithm is changed to ManualOff. This process is fully described in the following steps and shown diagrammatically in Figure A.1 to Figure A.4. Each ramp metering junction has a unique external Internet Protocol (IP) address that is entered into the Internet Explorer 1 (IE) address bar to access the site these addresses may be stored as Favourites within Internet Explorer. Once all ramp metering sites have a defined IP address then Atkins will provide a html file with all the IP addresses for the ramp metering junctions in a HA Area. To switch off a ramp metering system a User name, Password and Write Password is required and these will be notified to each organisation by Atkins. Each junction will have unique passwords The Ramp Metering system only supports the Microsoft Internet Explorer browser. Other browsers may work but results cannot be guaranteed. March 2008 A-9 MCH 2474

14 Ramp Metering Switch Off Process (1) Enter the IP address of the site to be accessed in the IE address bar. (2) Press Enter or Select Go. (3) When the Security Alert dialog appears select Yes to continue to the Login page. (4) The Supervisory Interface login page for the Ramp Metering site will be displayed. The name of the site appears in the top left had side. Check that the correct site has been accessed. (5) Complete the login information: (a) Enter a User name that has write access permissions. (b) Complete both the Password and the Write Password. (c) Press Enter or click Login. (6) Only one user can be logged in with write-access permissions. If someone is already logged in with write access permissions, repeat step (5) but tick the box to force the other user out. (Note, this will inhibit the other user making any further changes.) (7) When the Security Alert dialog appears select Yes to continue to the Supervisory Interface Home page. (8) In the Algorithms section click on the Configuration link to expand the options. (9) From the expanded Algorithms Configuration section click the SwitchOnOff link. (10) Wait for the SwitchOnOff Parameters page to be displayed. (11) Click the drop down box for the activationmode parameter. (12) Select ManualOff. (13) Scroll to the bottom of the page. (14) Click on the Submit button. (16) The screen will refresh and advise whether or not the update was successful. (17) The new activationmode is shown within the drop down menu. March 2008 A-10 MCH 2474

15 (18) Having completed the change of activationmode for the ramp metering site, log out of the Supervisory Interface using the link at the top right hand side of the page. Ramp Metering Switch On Process Repeat steps (1) to (18) above but at step (12) Select timedoccupancy. March 2008 A-11 MCH 2474

16 Figure A.1 - Switch Off Process Steps 1 to 6 March 2008 A-12 MCH 2474

17 Figure A.2 - Switch Off Process - Steps 7 to 8 March 2008 A-13 MCH 2474

18 Figure A.3 - Switch Off Process - Steps 9 to 14 March 2008 A-14 MCH 2474

19 Figure A.4 - Switch Off Process - Steps 15 to 18 March 2008 A-15 MCH 2474

20 Appendix B Traffic Management Considerations A typical ramp metering system comprises of four signal heads, ten pairs of slip road loops and five main carriageway MIDAS outstations. The ramp metering controller is located either on the nearside of the slip road or the nearside of the mainline within a standard communications cabinet. The slip road loops and outstations continually read traffic data from the slip road and the mainline. The ramp metering system operation relies on this continuous stream of traffic data and varies the vehicle release flow over the stopline (via the ramp metering signal sequences) according to the data values obtained from the road side. If traffic management is deployed within the vicinity of the ramp metering system, the traffic behaviour will become altered in the area. As the ramp metering system is finely calibrated at each site to reflect the individual characteristics of that site, significant changes to the traffic behaviour will affect the ramp metering system operation in a negative way. The Figure B.1 below highlights the parts of the network ( the Vicinity ) which feed data to the ramp metering system. If any traffic management is required to be deployed in the vicinity, the TechMAC should be advised so that the appropriate action may be taken. Pairs of slip road loops Ramp Metering Enclosure Signal Heads 500m No TM ½ mile No TM ¼ mile ~ 500m MIDAS Outstations Diagram not to scale This is the area in which TM can affect ramp metering operation. In the flow chart below, this area is termed the vicinity of Ramp Metering Figure B.1 - The Ramp Metering Vicinity It is advised that the local Area Road Space Booking applications are modified to include a section relating to the potential impacts on ramp metering. March 2008 B-16 MCH 2474

21 Figure B.2 below illustrates the information that needs to be obtained and how various TM interactions with a ramp system are to be handled. Figure B.2 - Dealing with TM in the Ramp Metering Vicinity March 2008 B-17 MCH 2474