The Traffic Signs Manual Chapter 8 Part 1: Design (2009) gives guidance for relaxation scheme road works which involve the temporary closure of one or more lanes on the carriageway. Advance warning signs are placed in the approach and lane change zones of road works, in order to inform road users that there are road works ahead, and also which of the lanes remain open to traffic and which will be closed to traffic. Supplementary guidance to Chapter 8 provides a number of alternative Temporary Traffic Management (TTM) techniques which use a reduced number of advance warning signs provided on A-frames at ground level. Advance warning signs are typically placed on the verge (nearside) 1 mile, 800m, 600m, 400m and 200m in advance of the first cone of the entry taper of the lane closure. For single offside or nearside lane closures on dual carriageway roads where the national speed limit applies, advance warning signs can alternatively be placed both on the verge and on the central reserve (offside) 1 mile, 800m and 400m in advance of the first cone. These TTM techniques for relaxation scheme road works still require road workers to set out these advance warning signs, an activity which exposes them to high risk. Therefore further alternative measures for providing advance warning signs in order to inform road users that there are road works ahead — including which of the lanes remain open to traffic and which will be closed to traffic — are being developed. Consequently, a programme of work was initiated to investigate the feasibility of using electronic Variable Signs and Signals (VSS), which are installed across the network and currently used to manage incidents and events, in place of conventional signs on A-frames at ground level to display lane closure information. This research project has specifically sought to evaluate the use of MS4 Variable Message Signs (VMS). The specific outcomes that the Agency was seeking from this task were: ??Outcome 1: Evidence of whether lane closure information displayed on MS4 VMS for advance warning of road works on relaxation scheme works are as effective as (or better than) existing methods (i.e. Chapter 8 and IAN 150/14 Revision 2 TTM) in terms of driver behaviour; * Outcome 2: Evaluation of the risk benefits to road workers associated with the elimination of the placement, maintenance and removal of temporary advance signing. * ?Outcome 3: An understanding of likely implications for — and impacts on — the Traffic Officer Service (TOS), which is responsible for the management of VSS, if road works were to be routinely signed using MS4s. As well as fulfilling the specific objectives described above, additional tasks were carried out as part of this project, such as a review of literature exploring the effect of different signing on driver behaviour on the approach to road works. The assessment of the effectiveness of MS4s as the sole means of signing works was achieved primarily by analysing traffic behaviour during a series of lane closures signed using the existing method (control) in use at the time of the trial and comparing this against driver behaviour during a series of lane closures signed using MS4 VMS (experimental). The sampling design created for the trial was based around experience gained from previous signing trials and involved the proposed collection of 15 nights of data for single lane nearside (lane 1) closures and 15 nights of data for single lane offside (lane 3) closures for both control and experimental conditions. A balanced design was proposed to ensure that variations in traffic flow, composition and driver behaviour throughout the week were controlled as far as possible. Covert video recording, using camera systems provided by TRL (the UK’s Transport Research Laboratory), allowed the measurement of traffic flows and the effect of signing the works using MS4s on driver lane choice and behaviour. The Measurement of Injury Risk (MIRi) Index applies to the deployment and retrieval of TTM for relaxation closures, considering the risk to road workers only. The MIRi tool quantifies risk using three factors: ?Likelihood of collision ?Duration of exposure ?Severity of injury in such collisions The scores generated by the tool provide an indication of the relative risk to road workers when installing and removing TTM using various techniques including those already in widespread use by the Traffic Management (TM) industry. Using the tool quantifies the risk to road workers associated with installing and removing TTM only and does not take into account differences to the risk associated with working within a closure. The omission of conventional signs on A-frames at ground level in advance of the road works was examined using the principles of the MIRi Index. In terms of the risk to road workers, this replicates the scenario in which suitable advance signing for drivers is provided by VSS instead. The likely implications for — and the impacts on — the TOS which is responsible for the management of VSS were considered in terms of both the availability of the technology infrastructure and staffing resources through an analysis of data and feedback from East Regional Control Centre (ERCC) staff. The on-road trial was successful in demonstrating that the use of MS4 VMS to display the advance warning of lanes open and lanes closed for road works are at least as effective as IAN 150/14 Revision 2 and Chapter 8 TTM. In this respect the on-road trial provided confidence that Outcome 1 was achieved. For nearside (lane 1) closures, the results showed that the pattern of vehicles changing lanes between the 800m to 400m distances did not differ between the experimental and control groups, and that the pattern of vehicles changing lanes between the most upstream sign containing lane closure information and the 400m sign did not differ between the experimental and control groups. For offside (lane 3) closures, the results showed that the pattern of vehicles changing lanes between the 800m to 400m distances did not differ between the experimental and control groups. The pattern of vehicles changing lanes between the most upstream sign containing lane closure information and the 400m sign differed in the middle lane, which was not safety-critical. The MIRi Index estimates that the risk to road workers when installing and removing TTM using only MS4s to provide advance warning signing is 18% lower for nearside closures than when using Off Side Signs Removal, and 30% lower for offside closures than when using Sign Simplification. It is safer still relative to the risk to road workers when installing and removing a full Chapter 8 relaxation layout. The risk reduction in the case of MS4s arises from the reduction in total time it takes to install/remove the closure and the elimination of carriageway crossings to install the advance warning signs. Outcome 2 was therefore successfully demonstrated. With regard to Outcome 3, the on-road trial provided an understanding of the likely impact upon the TOS and the dependency this technique will have on MS4 VMS availability. The greatest impact upon the TOS is related to the level of resource that was required for this trial to constantly monitor the accuracy of the electronic setting displayed on the MS4s. Availability of fully functional MS4s (i.e. ones not exhibiting faults) was relatively low, with 29% of the required MS4s — and subsequently 66% of planned trials — being affected by a fault on one or more of the MS4s. The trial did not observe any occurrence where the availability of the MS4s was affected due to normal operations i.e. by an unplanned incident. The reliability of the MS4s is currently likely to be insufficient for them to be used as the sole method for signing relaxation works, irrespective of whether this approach is comparable to using ground level signing in terms of road user behaviour. Assuming these technological issues can be resolved, other changes to the current way of working would also be required to ensure that MS4s can be used to provide drivers with suitable advanced warning of road works. For example, the Agency would require a system which is intelligent enough and flexible enough to allow simultaneous signalling of incidents and road works. A dedicated system alarm for any VSS in use as the sole method for signing road works would also be beneficial. Other approaches that would represent a more significant shift from the current approach to managing VSS could mitigate the risk associated with this approach. For example: ??Management of VSS used to sign road works from a centralised unit, so that all Regional Control Centre (RCC) operators are able to operate all VSS across the network. This would make it more likely that an RCC operator would be available to deal with a VSS failure immediately that this is alerted. ??Providing on-road staff with alerts directly when the VSS relevant to their works fails. This would remove the risk of a delay in an RCC operator informing on-road staff of the failure. * ?Providing TM staff with the ability to control the relevant VSS in full, whether temporarily or otherwise. This would ensure that TM staff fully own the risk to on-road staff that would be associated with VSS failure. This could include testing of the relevant VSS in advance. This approach would require appropriate protocols for control of the VSS to be handed over temporarily from National Traffic Information Centre (NTIC) and the RCC to TM staff, so that they do not unwittingly overwrite the VSS. Although this approach is not dissimilar to the current situation, TM staff would be less likely to be aware of what is occurring on adjacent sections of the network, so this might introduce the risk that an incident close to the works is not signed. (Author/publisher)
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