Use of High Level Signs for Static Relaxation Works

Transcription

1 Transport Research Laboratory Use of High Level Signs for Static Relaxation Works by R Wood, M Palmer, C Reeves, I Rillie RPN2084 PSF E158 DRAFT PROJECT REPORT

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3 Transport Research Laboratory DRAFT PROJECT REPORT RPN2084 Use of High Level Signs for Static Relaxation Works by R Wood, M Palmer, C Reeves, I Rillie (TRL) Prepared for: Project Record: Client: PSF E158 Safety Evaluation of High Level Signs for Static Relaxation Road Works Highways Agency, National Health and Safety Team Mark Pooley Copyright Transport Research Laboratory February 2012 This Final Report has been prepared for Highways Agency for the sole purpose of Project Report Review. It may only be disseminated once it has been completed and issued with a final TRL Report Number. The views expressed are those of the author(s) and not necessarily those of Highways Agency. Name Date Approved Project Manager Jenny Stannard 10/02/2012 Technical Referee Iain Rillie 10/02/2011

4 When purchased in hard copy, this publication is printed on paper that is FSC (Forest Stewardship Council) registered and TCF (Totally Chlorine Free) registered. Contents Amendment Record This report has been issued and amended as follows Version Date Description Editor Technical Referee /02/12 First draft for review and comment RW IR 1 10/02/12 Issued draft report RW IR TRL RPN2084

5 Contents List of Figures List of Tables Executive summary iii v vii Delivery Matrix 1 1 Introduction History of on-road trial development 3 2 On-Road Trial 4 3 Trial delivery Experimental design Operational activity Data collection Traffic flow camera systems 8 4 Results of on-road trial Trial data Analysed vehicle numbers HGV Proportion Analysis Statistical analysis Results of statistical analysis Results summary 14 5 Discussion 16 6 Conclusions and Recommendations Recommendations 18 Acknowledgements 19 References 19 Appendix A Operational Deployment and Retrieval 20 Deployment process 20 Retrieval process 20 Appendix B Camera Systems 21 Appendix C Analysis of Trial Data: Factors 22 TRL i RPN2084

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7 List of Figures Figure 1: High level signs used in Europe and the UK... 2 Figure 2: Chapter 8 Relaxation, control condition... 4 Figure 3: HLS Technique during deployment... 4 Figure 4: High Level Signing with taper in place... 5 Figure 5: Control video imaging locations... 5 Figure 6: High Level Sign Vehicle... 7 Figure 7: Typical camera views (left image from 'control' 200 yard sign, with taper and sequential lamps visible, right image from HLS vehicle)... 8 Figure 8: Proportion of vehicles in each lane Figure 9: Lane 3 occupancy by measurement point Figure 10: Recorder case, cover removed, showing battery and recorder Figure 11: Camera and mounting clamp Figure 12: Number of vehicles at each sign point in each trial Figure 13: Proportion of vehicles in each lane at each sign point Figure 14: Proportion of vehicles in each lane in each trial TRL iii RPN2084

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9 List of Tables Table 1: Trial measurement distances... 5 Table 2: Number of vehicle observations in each trial condition... 9 Table 3: Average, maximum and minimum proportion of vehicles observed across sites at 800yds and percentage point change at 200yds Table 4: Number of vehicles at each sign point Table 5: Number of vehicles in each lane Table 6: Number of vehicles in each experiment TRL v RPN2084

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11 Executive summary One of the highest risk activities for traffic management operatives is exposure to live traffic whilst deploying and removing temporary traffic management (TTM) signs. The greatest risk in this operation is arguably crossing the live carriageway to the central reserve. If this requirement could be eliminated or reduced without significantly increasing the risk to road users, this would immediately reduce the risk exposure of road workers and assist with delivering the Highways Agency Aiming for Zero programme and Exposure:Zero target. Vehicle or trailer mounted High level Variable Message Sign panels (referred to within this report as High Level Signs ) are used in Europe to provide advance warning of road works lane closures. Their use requires no carriageway crossings to set out road works and is significantly quicker than the manual installation of fixed temporary signs. The Highways Agency undertook an initial off-road evaluation in 2009 of a high level VMS sign trailer for this purpose, but subsequent evaluation found this type of equipment was impractical for reasons of cost and safety in the event of an impact. An alternative approach was proposed by A-One+, one of the HA s Service Providers, which would use three High Level Signs mounted at a height of 5 metres on existing Impact Protection Vehicles equipped with a Lorry Mounted Crash Cushion (LMCC). This approach would eliminate risk exposure associated with placing signs in the central reservation and also reduce risk associated with placing nearside signs. A trial was conducted to evaluate the safety and road user behaviour evidence in support of widespread use of high level signs in place of static advanced signing. Utilising video recordings of passing traffic, evidence of any changes in driver lane use, merging and general behaviour was gathered. Analysis of this data collected by A-One+ and analysed by TRL for over 17,000 vehicles showed that while there is a difference in the lane selection behaviour of drivers entering the advanced signing and works areas the balance of traffic across lanes appears to be improved. Statistically there is no difference in lane occupancy between the experimental and control conditions; within the closed lane the technique is able to reduce lane occupancy at a greater rate than a Chapter 8 relaxation layout closure. At the 200yds point immediately before the entry taper the two techniques are directly comparable. In addition, there were no incidents or hazardous occurrences observed during either the experiment or control condition. The results from this trial suggest that the High Level Sign approach has the same effect on closed lane occupancy by the point 200 yards before start of the entry taper (the 200yds point) as a standard Chapter 8 closure. While the technique indicates that the lane selection behaviours do differ between the two techniques, the High Level Sign may also be able to achieve a greater rate of decrease in closed lane occupancy that the current standard lane closure layout as well as balancing flow across the remaining open lanes. The outcome from the trial therefore provides evidence that the trial was successful, demonstrating that the High Level Sign approach is as effective in reducing closed lane occupancy by the start of the entry taper as a standard Chapter 8 closure. TRL vii RPN2084

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13 Delivery Matrix The Highways Agency National Health and Safety (H&S) Team required research and development support to investigate whether it is possible to use the Mobile Lane Closure technique for advance signing of static relaxation layout road works on the motorway and trunk road network while still providing a safe environment for the travelling public and maintaining network capacity. Replacing the static advance warning signs in the central reservation currently used for advance warning of road works would greatly reduce the exposure to live traffic that traffic management operatives face when deploying signs. This task will evaluate the safety and road user behaviour evidence in support of widespread use of this technique. The objectives of this work programme are: Facilitate an on-road trial of the use of High Level Signs (HLS) for static relaxation road works Design and implement a methodology to monitor driver behaviour and reaction to the HLS technique used in the trial Design and implement a methodology to monitor driver behaviour and reaction to a set of conventionally signed road works Compare the safety performance of both sets of road works for both road users and road workers Report the key findings to the Highways Agency, including limitations of the HLS technique for static relaxation road works signing These objectives are delivered in the following sections within this report: Objectives: Objective is met by: Within: 1: Facilitate an on-road trial of the use of High Level Signs (HLS) for static relaxation road works 2: Design and implement a methodology to monitor driver behaviour and reaction to the HLS technique used in the trial - A summary of the methodology used for the trial Methodology successfully used during previous on-road trial utilised Sections 2 & 3 5: Report the key findings to the Highways Agency, including limitations of the HLS technique for static relaxation road works signing - Analysis of the results obtained from the Statistical analysis of result carried Section 4 on-road evaluations out - Review of the effect of both the current Chapter 8 TTM configurations and the HLS configuration on lane merging behaviour and lane choice. Statistical analysis and discussion of result completed Sections 4 & 5 - An indication as to whether the data and conclusions of the study are robust to the point of being used to amend current Chapter 8 practices Statistical analysis of result undertaken and a summary of conclusions and associated recommendations Sections 4, 5 & 6 TRL 1 RPN2084

14 1 Introduction One of the highest risk activities for traffic management operatives is exposure to live traffic whilst deploying and removing temporary traffic management (TTM) signs, particularly whilst crossing the carriageway to the central reserve. If this requirement could be eliminated or reduced without significantly increasing the risk to road users, this would immediately reduce the risk exposure of road workers and assist with delivering the Highways Agency Aiming for Zero programme and Exposure:Zero target. Vehicle or trailer mounted High level Variable Message Sign panels (referred to within this report as High Level Signs ) are used in other countries such as France, Austria, Germany and Belgium to provide advance warning of road works lane closures. High level VMS are also used on Impact Protection Vehicles (IPVs) in the UK as light arrows to provide advance warning of the presence of the IPV, as well as of closed lanes or hazards on the carriageway during temporary traffic management installation and removal. Figure 1: High level signs used in Europe and the UK High level sign devices are considered to have significant benefits for the deployment and removal of road works. The main benefit is to eliminate some specific risks to road workers. Current practice for installation and removal of road works requires setting out of six to ten temporary traffic management advance warning signs. These are positioned in pairs, requiring that three to five signs are carried across the live carriageway to the central reservation. This has always been considered necessary to warn drivers in the outside lanes (nearest to the central reservation) of the lane closure ahead, as the view of the signs on the nearside (verge) may be obscured. However, crossing live carriageways is a high-risk activity; the use of high level signs would eliminate this requirement while still providing effective warning for all road users of the lane closure Additionally, the installation of these signs takes a considerable time due to the requirement to wait for a safe and suitable gap in the traffic before crossing the carriageway. The use of high level signs has a potential to reduce the time taken to place and remove the advance signing at road works by a significant amount. This brings many benefits including reduced risk exposure for the traffic management operatives, increased time to undertake works on the carriageway ( working window ) and thus less risk of road works overrunning and causing delay or congestion. The trial described in this report sought to evaluate a high level sign system for the signalling of lane closures to traffic approaching short-term temporary ( relaxation layout ) road works on motorways. This report presents the results from this trial and outlines the effect on traffic behaviour of changing the advance warning signing from ground level fixed signing on both sides of the carriageway to high level signs only on the nearside (hard shoulder). TRL 2 RPN2084

15 1.1 History of on-road trial development The Highways Agency undertook an initial off-road evaluation in 2009 of a high level VMS sign trailer (as shown in Figure 1) for use in place of the fixed lane closure advance warning signs. These trailer signs were to be used to provide a sign panel at 7m above the hard shoulder of the carriageway and were investigated extensively but this type of equipment was found to be impractical for reasons of cost and safety in the event of an impact. During the investigations into the trailer signs, one of the Highways Agency Service Providers (A-One+) proposed that a new approach should be considered. This would use high level signs mounted at a height of 5m on existing Impact Protection Vehicles. This would bring the benefit of a multi-role vehicle, equipped with a Lorry Mounted Crash Cushion (LMCC), being able to provide the necessary advance signing without the safety and operational concerns involved with using trailers without impact protection on the hard shoulder. This solution would therefore eliminate risk exposure associated with placing signs in the central reservation and also reduce risk associated with placing nearside signs while managing the collision risk for road users. While the use of high level signs for static relaxation layout road works could ensure safer working conditions for road workers, it was considered essential that this was achieved via a balance of road worker and road user risk. Additionally, it must be acknowledged that this technique would not be appropriate for every road works site, although it does have significant potential to contribute to the Highways Agency s Exposure Zero targets. The Highways Agency National Health and Safety (H&S) Team therefore supported the trial of high level signs for advance signing of static relaxation layout road works on the motorway network, which was carried out by A-One+ in Area 12. TRL 3 RPN2084

16 2 On-Road Trial Obtaining the information necessary to determine whether high level signs (HLS) could potentially be used within standard Chapter 8 relaxation layout traffic management was achieved by means of an on-road trial. This evaluated the difference in road user behaviour and lane distribution between the control layout (Chapter 8) and experimental condition (HLS technique) for an offside lane closure on a three-lane motorway with hard shoulder. Traffic management contractors considered that on-road works could be undertaken within the closed lane under developed risk assessment procedures and thus the trial was carried out on the network within the established road works programme. During the trials, the control condition was a standard Chapter 8 relaxation layout as defined within Figure 2. Figure 2: Chapter 8 Relaxation, control condition The HLS trial used advanced signing based upon the layout for the Mobile Lane Closure (MLC) and defined in diagram MLC2 from Chapter 8, but amended to use a cone taper in place of the Impact Protection Vehicle (IPV) (Figure 3 and Figure 4) and required utilisation of the following vehicles: Three high level sign vehicles One Impact Protection Vehicle (IPV) The cone taper was set under the protection of the HLS vehicles as shown in Figure 3 Figure 3: HLS Technique during deployment TRL 4 RPN2084

17 Once the cone taper was in place the IPV was removed, whilst the HLS vehicles positioned at 800, 500 and 200 yards remained, as shown within Figure 4. Figure 4: High Level Signing with taper in place Measurement of the impact of the TM change upon driver and merge behaviour was recorded by analysis of video imaging. Video equipment was fitted to HLS vehicles or sign frames at the distances shown in Table 1. Table 1: Trial measurement distances Position (yds) Control Experiment Imaging equipment was directed downstream for both conditions as shown within Figure 5 (showing the control condition). Figure 5: Control video imaging locations TRL 5 RPN2084

18 3 Trial delivery The use of vehicle mounted 5m high level signs was proposed by the Highways Agency s Area 12 MAC, A-One+. The trial delivery was carried out within Area 12 by A-One+ as part of their routine maintenance operations. 3.1 Experimental design Limitations were placed on the suitability of works locations, such that work sites needed to be: On three-lane carriageways with a hard shoulder Not in close proximity to junctions, which could affect driver merging behaviour During overnight works In addition, it was decided that this initial trial should adopt a cautious approach and so works would be subject to all limitations and restrictions imposed by the Highways Agency or contractors. This included maximum traffic flow and Heavy Goods Vehicle (HGV) proportion as defined for the Mobile Lane Closure technique (the closest comparable technique). A-One+ staff were guided by the location criteria set out within the experimental design but were left to make the final decision on site selection. This was to ensure the safety of the traffic management operatives and road workers within the work zone, as A-One+ used local knowledge of site characteristics, traffic flow and local factors to minimise risk from the trial to their operatives and road users. Abort criteria were also set, enabling A- One+ to terminate the trial immediately in the event of any risk considered to be unacceptable. This approach had the benefit of ensuring that the choice of sites was representative of the type of sites where a technique such as this would potentially be used. Work sites used to collect data therefore included both planned maintenance activity as well as responsive maintenance, such as repairs to damaged barriers. The design of the trial was planned to ensure statistical significance within the results and experimental robustness. The trial was planned to consider ten HLS closures (experiment) and a minimum of ten Chapter 8 relaxation closures (control). Video data was recorded using traffic flow camera systems (see Section 3.4) for each control at 800, 600, 400 and 200yds and 800, 500 and 200yds for each experiment. Data for each condition was collected between Monday and Friday with at least one instance occurring upon each day of the week, to account for variations in traffic flow, type and behaviour which are known to occur. TRL 6 RPN2084

19 3.2 Operational activity Modified Variable Messaging Signs (VMS) were fitted to three A-One+ vehicles. These units were capable of displaying lane closure graphics and text, as shown in Figure 6, as well as the light arrow and red X legends. Figure 6: High Level Sign Vehicle The VMS were mounted upon 18t Incident Support Units (ISUs) equipped with a Lorry Mounted Crash Cushion (LMCC). The vehicles were positioned as per the standard operating procedure for MLC works, namely 800, 500 and 200 metres/yards from the start of the Lane 3 entry taper.deployment and retrieval of traffic management for the experiment condition was based upon that of the standard operating procedure (SOP) for the existing MLC technique, with the deployment and retrieval process as detailed in Appendix A. The approach taken for site selection and trial activity was highly successful and resulted in no reported risks, near-misses or hazardous occurrences during the trial period. 3.3 Data collection The trial plan required collection of data from ten control and ten experiment sites. In all, a total of 11 control and 11 trial sites were operated by A-One+. For each site, the data were verified as soon as the memory cards were received from A-One+; for a site to be valid all cameras had to operate and all data be recorded and retrieved correctly. A-One+ carried out deployment and retrieval of the camera systems during trials and undertook daily maintenance. Times, locations and weather conditions of camera deployments were logged. Video was recorded onto solid-state Micro-SD memory cards, which were returned to TRL for analysis. Post-collection verification of the initial data indicated that one of each of the control and experiment sites were operated in close proximity to slip roads and therefore these data were not included within the analysis. TRL 7 RPN2084

20 3.4 Traffic flow camera systems Camera systems were designed and manufactured by TRL to gather video recordings to allow traffic flow, lane occupancy and driver behaviour to be determined and analysed. These systems allowed for data to be collected on lit and unlit carriageways. From the 200 yard sign position experience has shown it is usually possible to track a vehicle s position to the start point of the taper. TRL uniquely identified each camera system corresponding to a sign (A-frame or High Level Sign) measurement distance and provided labelled storage and despatch envelopes for each memory card to assist with the accurate return of camera data. There were two versions of the camera systems: Sign; placed on the sign frame for the duration of each set of road works and removed before the signing was retrieved High Level Sign; cameras remained on the vehicles for the duration of each set of road works and then removed, as vehicles remained in full use for daily incident support duties. Typical camera images are shown in Figure 7. Figure 7: Typical camera views (left image from 'control' 200 yard sign, with taper and sequential lamps visible, right image from HLS vehicle) Analysis of both lane occupancy and traffic behaviour was made possible by installing these camera systems upon the advance wicket sign frames at 800, 600, 400 and 200 yards for the control condition and upon HLS vehicles at 800, 500 and 200 yards for the HLS experimental condition. TRL 8 RPN2084

21 4 Results of on-road trial 4.1 Trial data Details of the data collection process are provided in Section 3.3. Robust control data (consisting of appropriate data from all cameras) were available from 10 of 11, of each of the control and experimental sites surveyed. This data was subsequently analysed to quantify the number of vehicles passing through the works area for comparison with the experiment data. The 10 valid trial nights provided data regarding the behaviour of in excess of 9,000 vehicles through the advance sign area. Due to higher flow rates in the experiment a smaller number of vehicles were recorded within the control data. 4.2 Analysed vehicle numbers The trial analysed data from a number of Lane three road works sites for durations of between 1 and 2 hours, with lane usage and behaviour recorded for more than 17,000 vehicle observations. Table 2 shows the sizes of samples analysed for each of the trial conditions. Table 2: Number of vehicle observations in each trial condition Experiment Vehicle count Control 8,614 Experiment 9,199 Due to the constraints associated with collecting data from operational roadwork sites, variance in flow and trial duration (and thus total number of vehicles counted for the trial and control conditions) was recorded across the experimental period HGV Proportion High sided vehicles such as Heavy Goods Vehicles (HGVs) can obscure nearside signing, whilst higher numbers of HGVs travelling at a limited 56mph are likely to influence lane choice made by other vehicles and the point at which near side signs can be read. The proportion of HGVs was thus recorded to understand their potential influence on driver behaviour due to obscuration effects. As offside signs were removed completely for the experimental condition the HGV proportion guideline used was as defined for the Mobile Lane Closure (MLC) technique, namely 15-20% with a maximum flow of 2700 vehicles/hour for a 3 lane carriageway. Increased HGV content is allowable with a converse reduction in overall flow i.e. at 30% HGV content the vehicle flow levels should be reduced by 10%. The recorded proportions vary between 9% and 27%, except in very low flow occurrences of around 400 vehicles/hour where HGVs made up a disproportionate amount (up to 50%) of the traffic. 4.3 Analysis The analysis sought to determine from vehicle lane occupancy data and visual observations of driver performance how driver behaviour was affected by the use of the High Level Sign. In particular, the trial sought to understand if driver behaviour during the use of the HLS technique could be considered acceptable when compared to driver behaviour when a Chapter 8 relaxation layout closure was used. TRL 9 RPN2084

22 Proportion of vehicles in lane Draft Project Report The data recorded allows the proportions of vehicles in each lane at each measurement point to be calculated for both the experimental and control conditions. Figure 8 shows the proportions of vehicles at each sign point in the control and experimental groups in Lanes 1, 2 and 3 respectively. 100% 80% 60% 40% 20% 0% Sign point (yrds) Lane 1 Control Lane 2 Control Lane 3 Control Lane 1 Experiment Lane 2 Experiment Lane 3 Experiment Figure 8: Proportion of vehicles in each lane Differences in lane selection and merge behaviour between the experimental and control groups are evident within the data; for example, lane occupancy for Lane 2 is around 10% higher for the HLS condition than for the control. However, it appears that there is little difference in the total level of traffic in the open lanes (Lane 2 and Lane 1) and that the distribution of traffic remains largely unaffected by the use of the High Level Sign. Lane occupancy in Lane 1 increases slightly across the lane change zone within the control data with a more marked increase for the experimental condition. For both experiment and control conditions the occupancy in the centre lane (Lane 2) remains essentially constant. This suggests that for both experiment and control layouts the net effect is for the same amount of traffic to be displaced into Lane 1 from Lane 2 as is displaced into Lane 3 into Lane 2. This is shown in Figure 8 by the essentially horizontal lines for the proportion of vehicles in Lane 2. It is clear from Figure 8 that traffic behaviour is therefore broadly comparable, with no sharp changes in levels of lane occupancy. This effect is tested statistically across all lanes in Section 4.4 but it appears that Lane 3 occupancy is closely comparable from 800 yards to 200 yards, namely throughout the entire length of the approach zone. Further detailed examination of Lane 3 occupancy, as shown in Figure 9, provides a better understanding of the pattern of lane change behaviour for the closed lane. TRL 10 RPN2084

23 Proportion of vehicles in lane 3 Draft Project Report 6% 5% 4% 3% 2% 1% 0% Sign point (yrds) Control Experiment Figure 9: Lane 3 occupancy by measurement point Within this graph, the scale on the left allows the small differences between lane occupancy to be seen. When assessing the Lane 3 (closed) lane occupancy and change behaviour as shown in Figure 9, the values are close and comparable at all sign points. At 800yds 3.5% of the traffic is in the closed lane within the control condition and 5.5% for the experimental condition; by the point 200 yards before start of the entry taper this has dropped to 1.2% and 1.5%, a difference that is negligible. It is also worth noting that the gradients of the two lines (the rate at which lane occupancy changes) are thus similar in shape, indicating that driver behaviour across the lane change zone is comparable. The experimental condition perhaps achieves a more linear decrease in lane occupancy than occupancy for the control, although this may be an artefact of the data. However, the linearity of decrease for the experimental condition does clearly suggest that drivers are therefore not waiting to vacate the closed lane until they are within sight of the entry taper with its sequentially flashing road danger lamps. Instead, the response appears to be a smooth transition from Lane 3 (the closed lane) into Lane 2, achieving the displacement of an equivalent amount of traffic from Lane 2 into Lane 1 as shown in in Figure 8. Therefore it can be stated that traffic moves from Lane 3 into the open lanes in both cases, with the experimental data showing a rate of decrease greater than that seen within the control. Within the experimental condition it is therefore strongly suggested that drivers are seeing and responding to the information given on the three High Level Signs and vacating the closed lane in a safe manner. The rate of decrease is greater with High Level Signs than for the control Chapter 8 condition, which may suggest that the experimental condition has a better effect on road user behaviour than the control. However, it must be noted that this technique may benefit from the effect of novelty and that perhaps in the longer term such an effect (if real) may not be sustained. Examining lane occupancy across the whole carriageway shows that the proportions of traffic across the lanes is broadly comparable between experiment and control, although the data show a wide spread of values for traffic counts. Table 3 shows the average, maximum and minimum proportions of vehicles in each lane at 800yds and the change at 200yds for both the control and experimental group: TRL 11 RPN2084

24 Table 3: Average, maximum and minimum proportion of vehicles observed across sites at 800yds and percentage point change at 200yds Lane Control Experiment 800yds Mean (Min, Max) L1 60% (52%,88%) L2 37% (12%,42%) L3 4% (0%,5%) Change at 200yds Mean (Min, Max) 2% (-15%, 6%) 0% (-5%, 15%) -2% (-4%,0%) 800yds Mean (Min, Max) 48% (36%,63%) 47% (37%,57%) 6% (1%, 11%) Change at 200yds Mean (Min, Max) 6% (0%,11%) -2% (-9%,1%) -4% (-8%,0%) The data above show that the proportion of vehicles in Lanes 1, 2 and 3 changes by 2%, 0% and -2% in the control group and 6%, -2% and -4% in the experimental group. Although the proportion of traffic within the closed lane experimental group is higher at the beginning of the lane change zone (800yds), the proportions for control and experiment within the closed lane at the 200yds point are the same. This again indicates that drivers respond well to both methods of advance lane closure signing. Once again, the difference in lane change behaviour for Lane 2 and Lane 1 can be seen. The effect on Lane 2 occupancy across the lane change zone is essentially zero, but there is a small decrease in Lane 2 lane occupancy within the experimental condition. It should be noted that the data are extremely noisy, due to small sample size when the data are divided by lane. However, despite this the table does again suggest that the experimental group behaviour is comparable to that of the control group when closed lane occupancy is taken as the measure. There also appears to be a slight change in overall lane selection behaviour (with a higher proportion of the traffic appearing in Lane 2 for the experimental condition). This results in equal proportions of traffic in each open lane; while the flows within this trial were low, at higher flows this effect could potentially help balance carriageway utilisation at the merge point and on the transition into the works, if found to be a repeatable effect. The effect of increased Lane 2 occupancy would need to be understood as this could have an influence on the availability of merge gaps within the lane. However, during the trial period the increased lane occupancy in Lane 2 appears to have little effect on the proportions of vehicles in Lane 3 and no negative effect upon their lane change behaviour. At the practical operational level, the contractors carrying out the trial were content to work within the closure and did not report any vehicles entering the hard shoulder, collisions/near-misses with the High Level Sign vehicles or road user vehicles striking the entry taper or longitudinal cone lines. 4.4 Statistical analysis The above analysis of the data examines the evidence for the effectiveness of the High Level Signs technique using a number of empirical approaches. In order to understand the data s significance, statistical testing was used to determine whether the behaviour of the vehicles within the lane change zone was statistically comparable for the control and experimental conditions. As vehicles are counted more than once (i.e. at 800, 500 and 200yds) within the experiment, a repeated measures ANOVA statistical method was used to identify the TRL 12 RPN2084

25 effect of the two advance signing options on lane change behaviour. Specific attention was paid to the behaviour of occupants of the (later closed) third lane. To identify changes to lane change and selection behaviour, analysis of three different factors was undertaken: Lane used (L1-L3); Sign/measurement position ( ); Condition type (Control and Experiment). The repeated measures ANOVA detects statistically significant differences within each factor, e.g. whether there is a difference in the number of vehicles in each lane, and within interactions, e.g. whether the change in the number of vehicles in each lane varies by experiment. In order to identify whether changes to road works signing as demonstrated within the trial affected lane change behaviour, consideration was given to the interaction between the three factors: lane used, sign/measurement point and experiment type (trial condition). Control data were collected at sign points 800, 600, 400 and 200yds and these data were compared to experimental data collected at sign points 800, 500 and 200yds. The control data were manipulated to match this pattern by averaging the number of vehicles counted at 600 and 400yds to estimate flows at the 500yds point in each lane Results of statistical analysis The results of the model show that some of the main effects and some of the interactions are indeed statistically significant. Where interactions are examined between factors, these are written as [factor 1] x [factor 2] Sign/measurement point: not significant (p>0.10) 1 The overall number of vehicles counted at each sign point is not statistically different, showing data capture was effective. Lane: significant (p<0.05) There is a significant difference in the overall number of vehicles in each lane. This is again as expected with usage of a carriageway regardless of whether road works are present or not. Experiment: not significant (p>0.10) There is not a significant difference in the overall number of vehicles in each condition (see Table 2). Sign point x experiment: not significant (p>0.10) There is no significant difference in the number of vehicles at each sign point across the different conditions. That is, if the number of vehicles reduced from the 800yds to 200yds in the control group then a statistically similar pattern was observed in the experimental group. Sign point x lane: significant (p<0.05) Differences in the number of vehicles at each sign point do vary by lane. As expected, at each sign point there was an overall difference in the distribution of vehicles by lane due to vehicles vacating the closed lane and similar numbers of vehicles moving from 1 Statistical significance is classified in two categories within this report. A p-value<0.05 indicates that we are 95% confident that this result is significantly different. A p-value<0.10 indicates that we are 90% confident (less confident) that this result is significantly different. TRL 13 RPN2084

26 Lane 2 into Lane 1. In this case there was a reduction in the overall number of vehicles in Lane 3 by the 200yd point and an increase in Lanes 1 and 2. Experiment x lane: not significant (p>0.10) The distribution of vehicles across the lanes does not differ (statistically) by experiment. As discussed in Section 4.3, the absolute proportion of vehicles in Lane 2 in the experimental group was higher (46%) than the proportion of vehicles in Lane 2 in the control group (37%) and vice versa for Lane 1 occupancy. However, statistically speaking this variation is not significant and could occur naturally. This suggests caution must be taken when considering that the balancing of vehicle flow by lane may be advantageous and would require further evaluation before claiming it as a benefit. Sign point x trial x lane: significant (p<0.10) Taking into account all other factors and interactions discussed above, which are mostly a factor of the study design, the interaction between sign point, experiment and lane is significant (at the 10% level). That is, it is possible to be 90% confident that the pattern of vehicles moving lanes differs between the experimental and control groups and that this difference does not occur purely by chance as a result of random variation. This finding indicates that the traffic does behave differently between the two conditions. Such a finding is unsurprising when it is considered that this trial involved comparison of two extremely dissimilar methods to influence the traffic, albeit with the aim of achieving the same overall result. In many ways, it would have been more surprising if the statistical analysis had been unable to demonstrate that the overall interaction resulted in a statistically significant difference in the data, as this would have suggested the sample size was inadequate or the experiment was flawed. The key to understanding the results of the ANOVA that shows that lane change behaviour is not statistically the same between the two techniques is to examine the outcome of the experimental and control conditions. The effect on Lane 1 and Lane 3 occupancy has already been shown but examining the data appears to show that High Level Signs are at least as effective in achieving a satisfactory lane occupancy distribution upstream of an entry taper. It is possible that the High Level Signs are in fact more effective, achieving a higher rate of decrease in closed lane occupancy compared to standard Chapter 8 signing. On this basis, it is considered that the result indicating driver behaviour is statistically dissimilar reflects a positive (statistical) difference in recorded lane occupancy and across the lane change zone recorded in Lane 3 for the experimental condition. It is therefore suggested that the High Level Sign approach can be deemed at least as effective in reducing closed lane occupancy by the point 200 yards before start of the entry taper (the 200yds point) as a standard Chapter 8 closure and may be able to achieve greater decreases in closed lane occupancy than the current standard lane closure layout. The High Level Sign approach also has the potential to have the effect of balancing flow across the remaining open lanes Results summary Through assessment of over 50,000 vehicle observation points from in excess of 17,000 vehicles the following results were found: No clear, statistically significant difference in lane distribution exists between experiment and control; some differences in absolute proportions by lane can be seen which indicate how patterns of lane use change but these are not statistically significant. TRL 14 RPN2084

27 There were statistically significant differences between interactions; therefore the lane merge behaviour is not statistically comparable between both conditions due to the traffic in Lane 3 leaving the lane at a higher rate during the experimental condition compared to the control plus the amount of traffic moving from Lane 2 to Lane 1 varying between conditions. Although the results show that statistically there is a difference between the lane change behaviour of the two conditions, this occurs due to the higher rate of lane changing from Lane 3 during the experimental condition and the Lane 2 / Lane 1 transitions During the trial the proportions of traffic in Lane 3 (the closed lane) were consistent and closely comparable between the experiment and control Although no statistical difference in lane selection behaviour can be shown, a balancing of vehicles between Lanes 1 and 2 may have occurred Therefore although the two techniques cannot be considered directly equivalent at all levels there are some key similarities apparent It is therefore suggested that the High Level Sign approach can be deemed at least as effective in reducing closed lane occupancy by the point 200 yards before start of the entry taper (the 200yds point) as a standard Chapter 8 closure The High Level Sign may also be able to achieve greater rate of decrease in closed lane occupancy that the current standard lane closure layout as well as balancing flow across the remaining open lanes. TRL 15 RPN2084

28 5 Discussion The analysis of the driver lane choice data from the trial corresponds with the feedback from the contractor personnel and video evidence in that there is little change in road user behaviour when High Level Signs (HLS) are used. There are only small differences, both physically and statistically, in terms of lane selection and change behaviour between the trialled signing technique using HLS and the standard relaxation layout closure from Chapter 8, with statistical analysis suggesting good equivalence and much comparability. It appears from the data that the distribution of vehicles entering the works is slightly different (although not statistically). Although vehicles vacating Lane 3 at a higher rate than for the standard relaxation layout cause slight changes in the data through the approach zone, this is largely offset by the shift from Lane 2 to Lane 1 of an exactly or almost identical amount of traffic. The net result is a very small change in overall open lane occupancy across the lane change zone, resulting in the distributions for both control and experiment remaining largely unchanged. The lane choices of traffic entering the lane change zone are made upstream of the first (800 yard) measurement location and thus it is unknown why the entering traffic is distributed differently between experiment and control conditions. It is possible to develop a number of hypotheses for this difference; for example the presence of the VMS panels over the hard shoulder may influence driver lane choice or indeed the presence of the road works 1 mile fixed sign may do likewise. However without data it is impossible to state categorically why this effect is observed. The trialled technique bears some similarity to the results gained through the trial of a mobile lane closure (MLCT) used statically (Palmer et al., 2011). Both trials use comparable techniques with three advanced sign vehicles placed at 300yd intervals (800, 500 and 200) on the nearside. However, the proportion of vehicles occupying Lane 3 (the closed lane) for this (HLS) experiment are consistently lower than those recorded for the MLCT and are comparable with the control condition data obtained during that study. This would tend to suggest the performance of the High Level Sign is at least comparable to the existing and widely used Mobile Lane Closure (MLC) when considering the ability to inform a road user in the most disadvantaged lane (Lane 3) of the presence of a lane closure ahead. It is more probable that the HLS technique is superior to the MLC technique when potential for obscuration of the signing is considered. Within the data, Lane 3 occupancy and lane change behaviour is arguably of greatest interest, as driver approach to the closed lane can be considered as a marker for increased road worker risk. Through the works area the proportions are similar and by 200yds they vary from 1.3% recorded for the control condition to 1.5% for the experiment. Figure 8 shows that whilst Lane 1 and 2 show some differences, Lane 3 change behaviour and occupancy is comparable. A further practical outcome of the trial was to identify a number of challenges to the use of the HLS technique on a wider basis: Higher resource requirements: HLS requires 6 operatives - three within the HLS vehicles and three to deploy and remove the taper and work site. However, the contractor delivering the trial did suggest that a significant reduction in deployment time was recorded for the HLS trial when compared to that of a standard relaxation closure, with obvious potential resource benefits. Change in risk exposure: HLS vehicles left on hard shoulder pose a different risk if struck compared to fixed plate signs on A-frames; the LMCC fitted to the HLS vehicle is intended to manage impact only by light vehicles. In addition, if the decision is made that HLS vehicles will not be left unoccupied there is a significantly changed risk exposure for TM operatives Environmental impact / CO 2 emissions: Use of HLS vehicles left with the engine running increases the carbon footprint associated with road works. TRL 16 RPN2084

29 6 Conclusions and Recommendations High Level Signs (HLS) are used extensively in Europe for advance signing of road works. Their use eliminates the requirement for carriageway crossings to place central reservation signing, as specified in current guidance The on-road trials of the HLS technique were benchmarked against a relaxation layout single offside lane closure (to Plan DZB6 in Chapter 8) already used widely on the HA network Five pairs of advance warning signs (placed on both sides of the carriageway) were replaced with three HLS vehicles on the hard shoulder The experimental condition required zero carriageway crossings as it used an IPV based taper deployment method and nearside signing only. Contractors did not report any vehicles entering the hard shoulder or any instance of vehicles striking the HLS vehicles, taper or longitudinal cone lines Within the on-road trials, driver behaviour and lane occupancy of over 18,000 vehicles were assessed for a control layout (Chapter 8) and one experimental condition (high level sign technique). Detailed analysis of the lane occupancy proportion was undertaken for varying flow levels, areas and both lit and unlit motorway sections. Data indicated that lane occupancy did not differ significantly between the control and trial conditions; for example more vehicles occupied Lane 2 in the experimental condition than in the control, but this was not a statistically significant difference This change in lane selection behaviour may act to balance traffic flow across the carriageway and potentially influence congestion risk through the works. Lane occupancy for Lane 3 (the closed lane) was closely comparable for both the trial and experiment, with differences negligible by the 200yd measurement point. It is therefore suggested that the High Level Sign approach can be deemed at least as effective in reducing closed lane occupancy by the point 200 yards before start of the entry taper as a Chapter 8 relaxation scheme layout The High Level Sign may also be able to achieve greater decreases in closed lane occupancy that the current standard lane closure layout as well as balancing flow across the remaining open lanes. Lane 3 occupancy was lower throughout the advance signing zone for HLS than for a Mobile Lane Closure used statically. Visual analysis of video data suggested that although lane change behaviour differed between conditions, no significant dangerous occurrences were identified. Contractors reported that deployment and overall work times were reduced significantly with the potential to reduce the effect of road works on Journey Time Reliability (JTR) A number of operational challenges will need to be addressed to enable the widespread use of this technique TRL 17 RPN2084

30 6.1 Recommendations The results from the analysis provide evidence that the trial was successful, demonstrating that the High Level Sign approach is as effective in reducing closed lane occupancy by the start of the entry taper as a standard Chapter 8 closure. However, the lane movement of vehicles in the different experimental conditions does differ slightly. Whilst the results of the analysis suggest that there is a statistical difference in lane change behaviour over the carriageway, the lane change behaviour of traffic approaching the closed lane (Lane 3) is comparable to the control and may therefore be considered acceptable. However, it is suggested that the increased proportions of traffic recorded in Lane 2 (adjacent to the closed lane) may need further assessment to ensure that it is not considered to unduly increase risk of incidents along the longitudinal cone line. Therefore, it is recommended that caution is exercised in rolling out this approach. It is also recommended that the risk of placing signs on the offside (via carriageway crossings) versus the potential change in risk exposure through changing the proportions of vehicles travelling in each lane a form of acceptability should be examined to ensure the overall risk balance for road workers remains acceptable. It is also recommended that further consideration is given to the proportion of Heavy Goods Vehicles (HGVs) in higher flow situations to ensure any obscuration of near side high level signs does not provide a negative effect on closed lane occupancy and merge behaviour. The operational issues and concerns highlighted by the MAC regarding the requirements for providing and deploying HLS may also need to be addressed if the expectation is that this technique will be adopted on a widespread scale. The fiscal challenge of modifying vehicles to operate the HLS technique should not be overlooked but it is considered that the cost and resource savings achievable from this technique would make the cost:benefit of such modifications positive for both the Highways Agency and their Supply Chain. It should also be noted that manufacturers have suggested that equipping new IPVs with the capability to operate as high level signs is likely to be far more costeffective than retrofitting existing vehicles. It is considered that this technique has significant potential to assist with delivering the Highways Agency s Aiming for Zero (AfZ) targets to eliminate carriageway crossings by 2016 (Exposure:Zero). TRL 18 RPN2084

31 Acknowledgements The work described in this report was carried out in the Road Safety Group of the Transport Research Laboratory. The project team wish to thank Stuart, Cordier, Phill Beaumont, Barry Hinchliffe and Danny Jameson of A-One+ for their initial concept and ongoing support in developing the concept from idea to delivery. References Department for Transport/Highways Agency (2009) Traffic Signs Manual, Chapter 8, TSO: London, UK. Department for Transport (2002) The Traffic Signs Regulations and General Directions, TSO: London, UK. Palmer M, Wood R, Walter L and Rillie I, (2011) Use of Mobile Lane Closure Technique for Static Relaxation Works, Transport Research Laboratory (TRL): Wokingham, UK. TRL 19 RPN2084

32 Appendix A Operational Deployment and Retrieval Deployment process Deployment of the HLS trial condition requires 6 operatives (3 in HLS vehicles and 3 within the TM crew) and a total of 4 vehicles: 3 x High Level Sign Vehicles (HLSVs) 1 x Impact Protection Vehicle The process used for the deployment of the trial condition is detailed below: Step 1: HLSVs transit to work site and operate VMS whilst a traffic count is conducted Step 2: IPV transits to work site and takes position in lane 3 Step 3: Step 4: Taper and longitudinal coning deployed as per standard operating procedure (SOP) IPV leaves work area and returns at approx. 30 minute intervals to check site Retrieval process The process used for the retrieval of the trial condition requires the same vehicles and operatives as for deployment and is detailed below: Step 1: Step 2: Step 3: Step 4: IPV transits to work site IPV enters closure and crew begins to retrieve closure IPV leaves work area Instruction to remove signing is given and all vehicles depart TRL 20 RPN2084

33 Appendix B Camera Systems Each camera system consists of two main parts. The recorder case, containing the recorder and battery, was fitted with a power switch and loop for security. Figure 10: Recorder case, cover removed, showing battery and recorder The camera connected to the recorder box and was fitted to a mounting clamp. For the vehicle systems a longer lead was fixed between the camera position on the vehicle s sign and the recorder location Figure 11: Camera and mounting clamp Cameras were positioned on the downstream side of nearside sign frames and on a vertical support on the offside of the vehicle, to obtain a view of vehicles travelling away from the camera. TRL 21 RPN2084

34 Appendix C Analysis of Trial Data: Factors Interactions between factors are shown as x y in the text below. Sign/measurement point: not significant (p>0.10) The overall number of vehicles counted at each sign point is not statistically different. Table 4: Number of vehicles at each sign point Sign point Vehicle count , , ,813 Lane: significant (p<0.05) There is a significant difference in the overall number of vehicles in each lane. Table 5: Number of vehicles in each lane Lane Vehicle count Lane1 28,964 Lane2 21,968 Lane3 1,509 Experiment: not significant (p>0.10) The total number of vehicles observed in each experiment was not statistically different. Table 6: Number of vehicles in each experiment Experiment Vehicle count Control 24,966 Experiment 27,475 Sign point x experiment: not significant (p>0.10) Differences in the number of vehicles at each sign point are the same across the control and experimental groups. That is, if the number of vehicles observed increases from the 800yds to 200yds in the control group then a similar pattern was observed in the experimental group. TRL 22 RPN2084

35 Proportion of vehicles in each lane Vehicle count Draft Project Report 10,000 Control Experiment 8,000 6,000 4,000 2, Sign point Figure 12: Number of vehicles at each sign point in each trial Sign point x lane: significant (p<0.05) Differences in the number of vehicles at each sign point vary by lane. That is, as expected, at each sign point there is an overall difference in the distribution of vehicles by lane. In this case there is a reduction in the overall number of vehicles in lane 3 by the 200yd point and an increase on lanes 1 and 2. 70% Lane 1 Lane 2 Lane 3 60% 50% 40% 30% 20% 10% 0% Sign point (yrds) Figure 13: Proportion of vehicles in each lane at each sign point TRL 23 RPN2084

36 Experiment x lane: not significant (p>0.10) The distribution of vehicles across the lanes does not differ by experiment. Figure 14 shows that the proportion of vehicles in lane 2 in the experimental group was higher (46%), yet not significantly higher than the proportion of vehicles in lane 2 in the control group (37%) and vice versa for Lane 1 occupancy. Figure 14: Proportion of vehicles in each lane in each trial TRL 24 RPN2084