6 Definition of the Managed Crossing Scheme (August to November 2008) 6.1 The Managed Crossing
6 Definition of the Managed Crossing Scheme (August to November 2008)
6.1 The Managed Crossing
Taking together the outcome of the Stage 2 Corridor Report and the assessment regarding the potential use for the Forth Road Bridge, the options for optimising the scheme definition were considered. The key considerations were that:
- The Stage 2 Corridor Report concluded that the Full Corridor Scheme need not be implemented in full. Further work would be required to define the road improvement within the preferred corridor that would provide best value for money. The project planning work was therefore progressed to allow further detailed consideration to be given to the form and function of the junctions required and the extent of the road infrastructure improvements that should be provided (see Section 4).
- The Forth Road Bridge could be capable of adaptation for multi-modal use, including future tram/light rail use, and it was determined that this would be taken forward as a planning assumption (see Section 5).
- The scheme defined to combine the output from these separate exercises is referred to as the Managed Crossing Scheme.
6.1.1 The Forth Road Bridge within a Managed Crossing
Of the various options for utilising the Forth Road Bridge within a managed crossing, the option that fits most comfortably with the scheme objectives is for the existing bridge to be retained to carry only public transport, pedestrians and cyclists. This approach contributes in particular to the objectives:
- to increase travel choices and improve integration across modes to encourage modal shift of people and goods;
- to improve accessibility and social inclusion;
- to minimise the impacts of maintenance on the effective operation of the transport network;
- to support sustainable development and economic growth; and
- to minimise the impact on people, and the natural and cultural heritage of the Forth area.
Future public transport use could include a light rapid transit system in the form of high quality bus network, guided bus way or a rail based system.
The creation of a new public transport corridor will support the further development of the public transport interchange park and ride facility at Ferrytoll and the development of new facilities as planned by Fife Council. There is also the further potential to create a new park and ride facility at South Queensferry for West Lothian and local residents.
To complement the existing bridge as part of a managed crossing, the replacement bridge will carry heavy goods vehicles and general traffic, with greater reliability and with a reduction of carbon-generating congestion from incidents and breakdowns through the inclusion of wind shielding and the availability of hard shoulders.
Given the age and nature of the existing bridge, an element of unforeseeable risk cannot be ignored. If a future unforeseen circumstance means that the Forth Road Bridge would not be suitable to carry all potential light rapid transit systems, it is proposed that the Forth Replacement Crossing would be designed such that light rapid transit could be accommodated in place of hard shoulders.
6.1.2 The Network Connections within a Managed Crossing
The connecting road strategy looked initially at expanding capacity through additional road width prioritised for high occupancy cars (cars with more than 1 person). Given that this strategy carries the risk of overprovision for residual single occupancy vehicles, particularly during the peak commuting periods, and creates traffic management inefficiencies, a more focussed assessment was made of the connecting road provision.
Detailed analysis of traffic conditions indicates that, for the majority of situations, the existing network operates without congestion, and that peak period congestion is largely a factor of the close junction spacing along the A90/M90 corridor and driver reaction to that, rather than the inadequacy of a dual two lane motorway. Much of the congestion and queuing which is observed during peak periods at present is due to the interaction of traffic joining busy traffic on the main carriageway at closely spaced junctions.
It is proposed that these operational issues are addressed by the use of Intelligent Transport Systems in combination with local junction improvements. Intelligent Transport Systems, or ITS, as they are more commonly known, are technology systems that assist network operators in providing an efficient, reliable and safe transport network by providing a suite of tools to deploy temporary measures at a strategic or local level. These measures can be used to influence road user behaviour, to deliver policy objectives, or to manage planned or unplanned disruption or congestion on the network.
Intelligent Transport Systems have been shown to provide environmental, economic and social benefits through the achievement of smoother and more reliable driving conditions, reducing accidents, managing incidents and delays. Typical benefits are:
- Environmental: reducing vehicle emissions and improving air quality and noise levels by managing traffic flow to reduce congestion, prevent flow break down or relocate queues.
- Economic: ITS potentially provides a more cost effective alternative to road widening, while systems have been shown to reduce congestion, accidents and improve journey time reliability.
- Social: ITS has been used to manage the road space better, reducing accidents and delays, and enabling the emergency services to deal with incidents more efficiently (reducing the amount of time the network is out of operation). Traditionally ITS was provided as a reactive tool for operators to manage the network and invoke plans or procedures during unplanned and planned events, but more recently ITS has been deployed to support pro-active traffic management.
6.1.3 Objectives for ITS in the Managed Crossing Scheme
The ITS Strategy will provide complementary measures to support the operation of the Forth Replacement Crossing during normal and abnormal conditions on the network and in the wider context allow the Forth Replacement Crossing to be a managed corridor within the Traffic Scotland trunk road network. The design of the ITS provision is integral to the project and takes account of the specific strategic transport planning objectives for the Forth Replacement Crossing.
(a) Maintaining Cross-Forth transport links
Tactical management on the Forth Replacement Crossing will be developed to deliver optimum capacity within a safe, efficient and reliable environment and provide local information to road and public transport users. The ITS components that will allow network operators to provide tactical management include:
- Lane Control Signals – used for controlling each lane, displaying mandatory speed limits, general road sign aspects and other aspects for managing lane use.
- Tactical Message Signs – used for displaying text messages and/or multicoloured pictograms to drivers to provide tactical messages.
- Ramp metering – used to regulate the flow of traffic entering the mainline from a slip road according to current traffic conditions.
- Traffic Monitoring System – used for gathering traffic data and detection of incidents.
- CCTV – used for visual monitoring of the motorway.
- Bridge Traffic Control and Monitoring Facilities – to manage traffic on the each carriageway of the bridge under normal and abnormal circumstances.
- Emergency Telephone System – to provide a consistent approach across the trunk road network in the provision of roadside assistance through direct connection of roadside telephones.
(b) Strategic Network Optimisation
Strategic optimisation would be concerned with the use of the Forth Replacement Crossing within a Scotland-wide transport network allowing strategic and diversionary routing to minimise the impact on the trunk road network of incidents or major refurbishments. In time of emergency, strategic management optimisation, which would be implemented through interconnection with Traffic Scotland’s system for network management, would be undertaken to maximise the efficiency of the network as a whole. The ITS components that will allow network operators to provide strategic network optimisation include:
- Strategic Message Signs – used in conjunction with existing messages signs for displaying text messages to drivers to provide pre-defined strategic message sets.
- Communications network – to collect and disseminate real-time travel information through a variety of media and applications.
- Interface with Traffic Scotland – to allow the Forth Replacement Crossing to be managed as a corridor within a wider network.
(c) Improve Journey Time Reliability
The integration of the Forth Replacement Crossing journey time measurement system with the existing systems of the network will allow network operators to use the ITS applications of tactical and strategic management to provide consistency of journey through interventions and provision of information.
(d) Multi-modal Integration and Sustainable development
The new ITS facilities will be integrated with Traffic Scotland’s Intelligent Transport System and utilise the same platform that is designed to support system enhancements. The facilities will use real-time traffic information to determine corrective action or dynamically implement management strategies as traffic conditions change.
The ITS will be designed with a development and technology refresh regime so that the operator tools remain effective as traffic demand changes in future years.
The ITS components that will assist sustainable development and economic growth include:
- Real-time traffic and travel information, collection, exchange and dissemination between the road network and public transport interchanges and park and ride sites.
- Traffic signal provision and access/exit control to prioritise public transport and vehicles utilising ‘park and ride’.
(e) Minimise Effects of Maintenance
The design will optimise whole life-cycle costs but there will still remain requirements for maintenance activities, repairs to damaged infrastructure and renewal of infrastructure during the life of the Forth Replacement Crossing. The use of ITS to provide lane control, advance message signs and mandatory speed limits, will provide safety benefit to roadside workers and minimise the impact to road users through provision of information and timely management of the available capacity.
(f) Minimise Environmental Impact
ITS has been shown to reduce the environmental impact of traffic as a result of reduced vehicle emissions and fuel consumption. This is achieved by reducing the occurrences of flow breakdown and therefore minimising ‘stop and start’ and prolonged queuing of traffic. The following ITS components would be used to deliver these benefits:
- Lane Control Signals
- Variable Speed Control
- Tactical and Strategic Message Signs
- Ramp metering.
- Traffic Monitoring System to detect congestion
- CCTV surveillance to reduce the time of response to incidents.
6.1.4 Associated Road Improvements
The Managed Crossing Scheme will provide high quality approach roads to the new bridge. The existing junctions at Admiralty and Ferrytoll will be enhanced to protect and promote the developing area of Rosyth and to provide good quality connections for local communities. A new grade separated junction will be provided at South Queensferry and Junction 1a on the M9 will be enhanced to facilitate new access to the bridge from West Lothian.
To the south of the Forth, the alignment of the Managed Crossing Scheme is based on the Full Corridor Scheme, South Corridor Option 1, as described within the Stage 2 Corridor Report.
Figure 6.1 – Option under consideration South of Forth
A new road will connect the Forth Replacement Crossing to the existing A90 and M9 motorway spur in the vicinity of the existing Scotstoun Junction via 2.7km of new dual carriageway located to the south and west of South Queensferry. A new grade separated junction will be located between the new crossing and the Scotstoun Junction providing a connection to the A904, giving local access to South Queensferry and bus access to the existing Forth Road Bridge. The developing alignment and junctions in this area of the scheme are illustrated in Figure 6.1.
The new road will be dual two lane with hard shoulder provision between the replacement crossing and the new South Queensferry Junction. East of the South Queensferry Junction, the new road will be dual three lane with hard shoulder provision to tie in with the existing road which diverges to provide free flow links to the M9 motorway spur and the A90 local road to Edinburgh.
The redundant A90 road space between the existing Echline slip roads has the potential to be converted to provide a cost effective new Park and Ride facility for around 400 cars, utilising the existing road construction and lighting. This new facility would cater for travellers in South Queensferry and West Lothian. Further work will however be required to determine the feasibility of this option in consultation with the City of Edinburgh Council, SESTRANS and bus operators.
Figure 6.2 – Option under consideration North of Forth
To the north of the Forth, the alignment of the Managed Crossing Scheme is based on that of the Full Corridor Scheme North Corridor Option 1, as far as the Admiralty Junction. The new crossing will connect to the existing A90 at Ferrytoll via the provision of a new dual two lane carriageway with hard shoulder. The existing grade separated Ferrytoll Junction will be significantly upgraded to provide bus access to the Forth Road Bridge while also improving the existing connections to the local road network and the Ferrytoll Park and Ride Site. The developing alignment and junctions are illustrated in Figure 6.2.
To allow for the high percentage of weaving vehicles between Ferrytoll and Admiralty Junctions, the existing northbound A90 will be upgraded, largely utilising the existing alignment, to provide a dual three lane road by the provision of weaving lanes between the junctions. This will also involve improvements to the south facing slip roads of Admiralty Junction.
6.1.5 Carriageway Provision
In addition to the improvements between Ferrytoll and Admiralty Junctions described above, the road between the South Queensferry and Scotstoun Junctions will also be widened to dual three lanes, thereby improving the operational effectiveness of the network.
Hard shoulder provision will be wider than the standard 3.3m between the South Queensferry and Ferrytoll Junctions. This additional width will allow for usage by buses, when wind conditions preclude the use of the existing bridge, or by other forms of public transport if this becomes necessary in the future.
6.1.6 Associated Junction Improvements
The junction improvements are summarised below.
(a) Ferrytoll Junction
The existing grade separated Ferrytoll Junction will be significantly upgraded to connect the realigned A90 to the local road network serving Rosyth, Inverkeithing and North Queensferry. The junction will also provide a connection for public transport vehicles to the Forth Road Bridge. The integration of the Ferrytoll Park and Ride Facility is a critical aspect of the junction design and the reconfiguration of the access to improve the operational aspects of both the junction and the site will be incorporated within the design.
The new Ferrytoll gyratory will be repositioned to the north and, taking cognisance of the expected increase in activity in the Rosyth area from development of the Rosyth waterfront. The junction size will be expanded to improve the capacity of the junction. In order to maximise operational characteristics, signalisation of the junction is likely.
(b) South Queensferry Junction
The new South Queensferry Junction will provide local access from the realigned A90 to South Queensferry, the A904 and the Forth Road Bridge. To accommodate the volume of weaving traffic between Scotstoun and South Queensferry, the junction will be grade separated with a lane gain/lane drop configuration for the east facing slip roads reducing the mainline carriageway though the junction from three lanes to two. The west facing slip roads will have standard merge and diverge layouts onto the dual two lane connection to the replacement bridge.
A short link road to the north will connect the South Queensferry Junction to the A904. The new junction on the A904 will be located to the west of the existing Echline Junction and will likely take the form of a roundabout. Due to the close interaction between the new South Queensferry and A904 Junctions, signalisation may be required to improve junction efficiency.
Bus access to the Forth Road Bridge will be facilitated through the new South Queensferry Junction via the existing Echline Junction.
(c) M9 Junction 1a
In the facilitation of improved cross Forth connections, the junction between the M9 Spur and the M9 Junction 1a is to be enhanced to provide free flow connections to the west and the existing connections to the east will be refined. The developing junction layout is illustrated in Figure 6.3.
The interaction between the M9 Junction 1a and the Newbridge Junction located to the east has been recognised as a constraint on the operation of the strategic road network in this area. It is therefore proposed that the short section of M9 between the junctions will be upgraded to a dual four lane carriageway to cater better for the weaving movement of traffic over this section. This proposal would also permit the east facing slip roads from the M9 Spur to the M9 carriageway to be widened to two lanes improving the connectivity and operational performance of the junctions.
The potential high level of development growth in West Lothian is recognised and, with increased accessibility being a key objective, new west facing slip roads connecting the M9 and M9 Spur will be provided, catering for a movement that does not currently exist.
Figure 6.3 Junction 1a Layout