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Incident Screens - Functional Specification
Congestion caused by incidents is a significant cause of delay on the Strategic Road Network. In many cases, incidents can cause secondary congestion on the opposite carriageway due to road users slowing down to look at the incident scene (known as 'rubbernecking').
Blocking the passing drivers' view of the scene with an incident screen helps address this issue; work carried out by the TIM team has demonstrated the benefit of incident screens in reducing secondary congestion caused by 'rubbernecking'. Incident screens remain a key project within TIM and have been featured in the Bulletin on several occasions, the last article in June 2008 focused on a recent trial of a free-standing incident screening system in Area 5.
Incident screens have the potential to make a major contribution to traffic incident management and so the TIM team has produced a functional specification for incident screens to enable their use on a national basis. This article gives some insight into how the functional specification was developed and provides an overview of the requirements set out in the specification document.
Incident Screen Specification
The early work on barrier-mounted incident screens by TRL showed that a clear benefit could be realised by screening incidents, but that the use of barrier-mounted screens was limited because:
- If the incident has resulted in damage to the barrier the incident screen cannot be fitted
- No 'one size fits all' product exists for concrete, wire and steel barriers
- The screen can only mount on the barrier and cannot be erected anywhere else
Free-standing incident screens do not require any mounting points other than their own bases and so can be used anywhere on the carriageway. The TIM team recognised early on that there could be an issue with their stability, particularly in windy conditions. This resulted in on road trials and off road testing of various screen designs to establish their operational limits. Consequently, the on-road trial of a free-standing incident screening system developed by the Service Provider in Area 5.
The findings from the testing work carried out on behalf of the TIM team by TRL, and the trials in Areas 5 and 8 have contributed to the functional specification, which will be released by the Highways Agency in the near future. The specification document covers the performance of both barrier-mounted and free-standing incident screens in the following areas:
- Functional requirements
- Performance requirements
- Requirements for barrier-mounted screens
- Requirements for free-standing screens
- Operational guidance
A summary of the key points from the specification is given below; the full incident screen specification (75KB PDF) is available to view here.
These apply to all screens, regardless of their type. The functional requirements define the types of incident screens, including their requirement to "effectively block the view of the opposite carriageway". It sets the minimum height (2.0 metres from the carriageways surface) for screens.
The performance requirements also apply to all screens, and set out basic requirements for durability, weather resistance, stability and "fail safe" in the event of collision with or failure of the screen.
Requirements for barrier-mounted screens
Barrier-mounted screens require special consideration to ensure they do not compromise the function of the barrier in the event of a vehicle colliding with it. This part of the specification sets out what is and is not permitted for attachment to barriers.
Requirements for free-standing screens
The free-standing screen requirements set out the recommended dimensions of screens, what is and is not permitted to ensure the screens stability and this includes a requirement to demonstrate the stability of the screen in windy conditions. This can be achieved by either full-scale wind testing or (if the screen meets certain criteria) by a stability test contained in an Appendix to the specification.
Physical performance requirements
This applies to all screen types and sets out the requirements for transporting a screen to an incident, minimum rate of screen deployment and linking screens together. It also ensures that the deployment, use and removal of the screen does not cause a hazard for either the staff handling the screen or other road workers present at the incident scene.
A key section within the functional specification is a set of guidance notes on the operational use of an incident screen. This is to ensure that they are used for the correct purpose and in a safe and effective manner. Some of the points covered in the specification are detailed in the links below:
Available Incident Screens
Currently there are several incident screens in use on the network of the two different types; free-standing and barrier-mounted. Both of these options have been reviewed and trialled by the TIM team with the free-standing screen establishing itself as the favoured option, due to its versatility.
For more information on these two types of incident screens (228KB PDF), please follow the link.
The purpose of this article is to provide information about the screens which are available and the Highways Agency is aware of and will not endorse one particular product or supplier.
Previously, the Bulletin has focussed on two particular products, these being; the Wilchem incident screen, trialled in Area 8 and the internally developed screen in Area 5. Further information about the two is detailed below and available on request. In addition to this, the Axi-Shield has been brought to our attention; however this particular screen has not been trialled by the Highways Agency.
Wilchem - Free-standing Screen
An incident screen originally developed in the Netherlands but soon identified as 'good practice' by English incident responders. Initially it was a barrier mounted product; however it has since been re-developed into a free-standing screen, leading to it being tested and trialled successfully in England.
The screen is approximately 200 metres long and can be erected by two trained people in less than 15 minutes, however a further three people are required to implement traffic management around it. It is transported in a bespoke trailer, built specifically to assist in the deployment of the screen.
Please follow the link to view their website.
To see a previous article on this incident screens trial in Area 8 please follow the link.
Self-developed screen in Area 5
The screen in Area 5 was developed using an early draft of the functional specification, demonstrating that a bespoke incident screen can be developed internally by the Service Provider, provided it is tested and complies with the requirements of the specification.
For further information on the screen, please follow the link to a previous Bulletin article.
The Axi-Shield originated from a university course where students were tasked with developing a product, underpinned by a valid business case. Recognising the cost of 'rubbernecking' and congestion to the economy, a cheap and flexible screen was deemed to be a viable option.
The Axi-Shield is now an up and running business producing a mobile screen that expands longitudinally from modules, making it easy and simple to transport. It is approximately two metres high and can be deployed up to 80 metres long, in a prismatic structure which it claims to remain stable in winds up to 35mph. The system can be unfolded in less than fifteen minutes, requiring no manual lifting of heavy sections or on-site assembly and requires two operators plus a vehicle driver to set it up.
Please note that the Axi-Shield has not been tested by the Highways Agency.
To visit their website, please follow the link.
You can help us?
The TIM Team is seeking to capture best-practice in both incident screen design and use. As a result, we would like to hear from any manufacturers or suppliers of incident screening systems to learn about the capabilities of their systems. Similarly, if you are using an incident screen we would be interested in your experiences and successes. Please contact us at TIMBulletin@highways.gsi.gov.uk
Later this year, the Network Services Directorate (NetServ) and the TIM team will be issuing an Area Management Memo (AMM) introducing the specification and operational requirements for incident screens. The Highways Agency Area Performance Teams in partnership with their Service Providers will agree their incident screen requirements, including what type of screens are suitable for their part of the network. Once this is complete, screens will be procured before the end of the 2008/2009 financial year for deployment across the network.
The article focuses on incident screens that the Highways Agency is aware of. Inclusion in this article does not constitute an endorsement of any product or Service Provider by the Highways Agency.
Thanks to Iain Rillie from TRL for his assistance in the production of this article.