Select Committee on Environment, Transport and Regional Affairs Memoranda

Appendix A

Memorandum by TRL Limited (RM 16)


  1.  We welcome the opportunity to submit comment on the matters under consideration by the sub-committee namely:

    —  the current state of repair of roads;

    —  the steps taken by government, the Highways Agency, and local authorities; and

    —  possible future improvements.

  2.  We have written this memorandum in our capacity as an impartial research establishment, drawing on +our scientific knowledge rather than commenting on matters of policy. We have put greater emphasis on our knowledge of the approach to establishing the state of repair, rather than on the condition itself. We felt it also important to submit comment on the appropriate standard that should be achieved. Finally, we have commented on sustainability issues, including the use of quieter road surfaces and the recycling of materials, as requested. The link between research and application in these areas is a very close one and we have therefore attempted to set the operational context for much of the material relating to research in the submission.


The Current position

  3.  The current state of repair of trunk roads is expressed by the performance indicator for maintenance described in the Highways Agency (HA) Business Plan and Annual Report. Each year, the conditions of trunk roads and principal roads are also reported separately in the National Road Maintenance Condition Survey (NRMCS). The HA performance indicator is for carriageways only and does not apply to other parts of the road (eg footways or structures). The NRMCS is primarily for carriageways but also includes a summarised representation of the condition of footways.

  4.  Currently, the HA performance indicator and the NRMCS use different measures of condition for trunk roads. We welcome the review of the NRMCS (in progress) from which it is expected that a common reporting measure will be specified for trunk and principal roads.

  5.  The inspection of some components of the road structure that have a significant influence on the condition of the carriageway is not included in either the HA performance indicator or the NRMCS. For example, there is concern that the sub-surface drainage network of some trunk and principal roads is in need of attention but there is little hard evidence to support this concern.

  6.  The target level of condition for trunk roads aims at achieving a steady state, ie that no more than 7 per cent to 8 per cent of the network requires maintenance at any one time. The estimated proportion of trunk road network requiring maintenance at March 2000 is 7.5 per cent. But the target condition of principal roads in terms of the whole-life cost, or any other measure, has not been established. A further weakness of the present system is that, for both surface condition and pavement strength, there is no satisfactory way of comparing trunk roads and principal roads. The measures of condition are for asphalt roads only.

Steps taken

  7.  Current research (by TRL) is investigating what the target condition should be so as to minimise the whole-life cost of trunk road maintenance, evaluated in terms of maintenance works cost and the costs of disruption to road users at roadworks sites. All of the current reports on the state of repair of the trunk road network are based on levels of condition; in the future they will take into account the costs of future maintenance work. The HA has a performance indicator for lane availability on the road network but there is no equivalent for principal roads.

  8.  For trunk roads, the need for maintenance work and appropriate remedial treatment is established following clearly defined condition assessment procedures set out in the Design Manual for Roads & Bridges (DMRB). This process feeds through to the fund bidding and prioritisation requirements specified in the HA Bidding Pack, which Managing Agents should follow to ensure best practice in developing a programme of maintenance work that reflects value for money. The identification of maintenance needs and allocation of funds for principal roads follows a similar process. But there is an added dimension in a "political" factor; ie the final prioritisation of works is often influenced by Members' desires and does not necessarily reflect the ranking of the condition on the road network.

The Future

  9.  There is a need to ensure that sufficient resources are allocated so as to guarantee a successful implementation of the new NRMCS following completion of the review.

  10.  There is a need to improve the reporting of the condition of the road network, to include all pavement types (asphalt and concrete) in the network and to make it consistent across both trunk and principal roads. The target condition should be identified for each road type. This target should be set taking account of minimum levels of condition (such as skidding resistance), the whole-life costs of the maintenance works and the level of serviceability provided to the road user and those affected by the roads.

  11.  All reports on the state of repair are based on static measures of condition which are generally the average condition. An additional indicator could show how the condition is changing. At best, maintenance is carried out on only a small proportion of the network in any year and as some deterioration in condition is relatively slow, there is little change in the average network condition each year. Research (by TRL) for the CSS in 1997, showed that a better representation of the change in condition is given by the "tail" of the distribution of condition. The advantages from using this approach, in terms of quality of reporting, have not been fully exploited in any of the national reports.

  12.  Although historic results of condition allow trends to be shown, no reports are available which predict the likely future condition of the network. A useful extension to the traditional reports would be the expected future condition of the network under different assumptions, or at least under the current assumption, of future maintenance funding.

  13.  The state of repair of road networks is reported separately for each component of the road, ie carriageway, bridges, safety fences, signage and so on. The state of repair of both trunk roads and principal roads does not take into account the quality of ride or journey. Highway authorities have responsibility for all aspects and some way of reporting the combined state of repair for all components would allow summaries of the state of repair and performance of the whole of each network to be produced.

  14.  The objectives in the Ten Year Plan have led to a significant increase in maintenance funding for local roads. Although much of the increase will be for non-principal roads, it is a concern that there are currently insufficient assessment tools to report on the effectiveness of the increased maintenance expenditure on principal roads compared to those which exist or are being developed for trunk roads. The need for research to develop such tools is urgent.

  15.  Research is also required to assess the current state of drains on selected sections of the road network. This might also identify the need for further work on the design and detailing of drains. For assessing the condition of long lengths of pipe drains, it is likely that the use of CCTV surveys will become more widespread.

  16.  We consider the issues of recycling and quieter road surfaces in paragraphs 35 to 52 below.


The Current position

  17.  All highway authorities undertake inspections and structural assessments using detailed engineering standards and procedures, most of which have been developed by the HA (and earlier by DTp) with the close involvement of TRL. Structures are regularly inspected to determine their physical condition and structural assessments are carried out to determine whether structures can safely carry the required loading.

  18.  Structural assessments on bridges are being carried out as part of the national bridge assessment and strengthening programme that is nearing completion. Assessments have been undertaken on short span bridges designed prior to 1975 and longer span bridges ie those with a loaded length in excess of 50m. The assessment calculations take account of the physical condition of the structure as determined from the inspections. This will ensure that all bridge structures currently assessed to be sub-standard or unsafe will soon be either strengthened or otherwise safeguarded. Structural assessments on other highway structures are normally made where a structure shows signs of distress. However, there are no nationally published data to indicate how many structures are at present in an unacceptable state in terms of their material condition.

  19.  Maintenance work is currently triggered from the results of an inspection or a structural assessment. It is divided into three categories: essential, preventative and routine. Essential maintenance is required to maintain safety standards eg on structures that are assessed to be inadequate for the 40 tonne loading or because the condition of the structure is deteriorating to an unacceptable level which may cause public alarm or make the structural behaviour unpredictable. Preventative maintenance is work that is not essential but which is aimed at reducing future deterioration. Routine maintenance is work that should be carried out at regular intervals to keep structures in good order for example cleaning drains.

  20.  There is currently no recognised condition index for highway structures. Most structures are, in respect of their load carrying capacity and physical condition, somewhere between the "as new" state and the "unsafe" or "unacceptable" state but there is no means for knowing where the structures lie within this range. There is however evidence that some types of structure lie towards the unacceptable end of this range. There are also some types of structure that are difficult to assess.

  21.  Recent publicised figures on lighting columns throughout the UK have raised the awareness of street lighting engineers to the ever-increasing age and condition of the lighting stock. There are around 6.3 million columns in the UK, and it is estimated that around 700,000 columns are in urgent need of replacement. Nearly 30 per cent of the current stock of lighting columns is over 30 years of age and a further 2.2 million columns will reach this age within the next 10 years. Because most deterioration takes place internally and below ground the structural condition of columns cannot easily be identified. This is a major difficulty. Past under investment in maintenance and replacement has generated concerns about public safety.

  22.  The condition of substructures such as buried structures, and retaining walls are difficult to assess. The reliability of structural assessments of a corrugated steel buried structure is a problem because the method is highly empirical, and for anchored structures it is almost impossible to assess structural stability without information on the loads carried by ground anchorages. For these structures, judgement is largely based on inspection reports.

  23.  There are certain types of structure on the road network which are likely to be subjected to increasing risks in the future years. Such risk factors arise from vehicle impacts on bridge columns or bridge parapets, corrosion on tendons in post-tensioned concrete bridges and scour of the foundation supporting river bridges. As bridges age so the risk of fatigue in steel structures will also increase. Although investigations are being carried out in respect of these risk factors, there are at present no nationally published data to indicate the adequacy of the structure types concerned to withstand these risks.

Steps taken

  24.  In the past, maintenance was carried out following an inspection with the aim of returning the structure to its original state. More comprehensive procedures are now being introduced by the HA so that in the future maintenance is likely to be based on whole life costs and the sustainability of resources.

  25.  A good deal of research has been undertaken for the HA on the development of advice on the inspection and assessment of buried structures. Work has also been commissioned to determine best practice for the design, inspection, assessment and maintenance of ground anchored structures. Some of this was aimed at determining long-term performance. The final results of this work should come to fruition and be implemented in the near future.

  26.  A review of non-destructive techniques for determining the condition of lighting columns is underway. The development of a risk management strategy to enable maintenance engineers to prioritise the use of limited funding for the testing, maintenance, repair and replacement is also being undertaken to minimise the risk of injury to people and property. An inventory database has been identified as essential to compiling information about the condition of the national lighting column stock and it is anticipated that funds will be made available for its compilation in 2002.

  27.  There has been a relatively high incidence of shallow failures in embankments on the highway network. The HA has promoted research on assessing the likely rate of failure of slopes of different slope angles and in various types of soil. Risk assessment models have been developed from data of this type.

  28.  Methods of inspecting the condition of earthworks using remote sensing techniques are also under investigation. The use of risk assessment models based on the results of remote sensing surveys should become commonplace. This should help in the efficient management of earthworks. In addition it would seem necessary to undertake some defensive research to determine the likelihood of deep-seated failures in earthworks. A high incidence of such failures would have significant economic implications for owners and maintaining agencies alike.

The Future

  29.  The HA is currently developing and implementing new maintenance procedures for the Trunk Road Network. These include the structures strategic plan which will provide future expenditure profiles for different types of maintenance, whole life assessment and risks and options based prioritisation of works. These procedures could also be applied to local authority structures. A nationally co-ordinated approach is required to implement these procedures widely.

  30.  Research is required to determine the optimum maintenance strategy for structures at the network level to ensure that future maintenance is properly planned and peaks in expenditure avoided. Failure to do so might result in backlogs of work or periods of high expenditure since particular groups of structure may need rehabilitation all at the same time. The development of an optimum strategy would ensure that best value was obtained from the available funds for maintenance.

  31.  Maintenance strategies and programmes are required to safeguard structures against the increasing risks from Heavy Goods Vehicles collision, flood action and steel fatigue. Post-tensioned concrete bridges, a few of which around the world have suffered from catastrophic failure in the past, should be subjected to special attention.

  32.  Developments over the last 15 years have led to a fragmented approach to lighting column maintenance and to the tools that could assist in determining the structural condition. A risk management strategy, which allocates columns to a high, medium or low risk category is needed using data from accurate non-destructive test methods. It will allow prioritisation of maintenance based on real need.

  33.  Research is also required to determine the life cycle costs for lighting columns. Included in this will be the potential for reduction of the energy consumption of lamps and carbon dioxide emissions. Together with the structural assessment of lighting columns, a more cost-effective management strategy for the repair and replacement of lighting columns and luminares can then be realised.

  34.  There is a need to ensure that maintenance is properly resourced not only in terms of finance but also in terms of the availability of experienced maintenance personnel. Developments over the last few decades have meant that centres of expertise (local authority bridge offices, road construction units and regional offices) have changed and the engineering expertise has diminished. There has also been a loss of continuity due to constant changes in responsibility for road maintenance. This has meant that the whole process is becoming fragmented and there is an increasing tendency for those responsible to rely more on procedures than experience and engineering judgement. This needs to be addressed by paying greater attention to developing and retaining engineering expertise in the authorities and in other national bodies.


  35.  Sustainable development can be defined as Development that meets the needs of the present without compromising the ability of future generations to meet their own needs (Bruntland 1987). Sustainable Development and the contribution of Sustainable Construction practices are now at the foreground of DETR policy development. Because this is an all-encompassing issue, many individual themes relating to the sustainable construction and maintenance of roads are already addressed. They include whole-life costing, use of recycled, locally-won or alternative materials, road-user and workforce safety, use of low-noise surfaces, environmental management systems and so on. Some other issues are not yet adequately addressed, for instance, the development of performance specifications to allow innovation or alternative methods, monitoring of energy consumption and emissions, waste-management, road-user and neighbourhood consultation, considering the requirements of non-motorised users and permitting access, etc.

  36.  All of these things have a part to play in delivering more sustainable options for road repair, but there remains a requirement to bring the separate themes together to strike the right balance between sometimes conflicting objectives and to deliver workable changes to current practice. To do this will require a broad methodology for specification, procurement and developing best practice guidance. Some elements are already in place but others require development. A principal requirement is the development of an assessment system with which to measure progress against sustainability objectives, to benchmark and to set targets. The production and adoption of indicators, in line with DETR policy, is an essential part of this process and could be used in assessment both as part of condition monitoring, scheme appraisal and in procurement.

  37.  Specific issues of sustainability related to recycling and quieter roads are considered separately as follows.


  38.  In this context, recycling is taken to mean the re-use of materials already in the road, or the use of wastes or alternative materials to imported natural resources. Recycling road pavement materials can lead to reductions on the use of resources including aggregates, bitumen and cement. Where the process is performed in situ, or uses "cold-mix" technology, reductions can also result in energy consumption and the resulting emissions.

  39.  Foundation layers can be constructed using graded, granular waste materials, or stabilised locally-won soils etc, as an alternative to importing aggregates. Bound foundation layers can use industrial by-products (pulverised fuel ash, granulated blast-furnace slag) as alternatives to lime or cement.

  40.  Concrete can be recycled by crushing and reuse as aggregate. This has proved more popular in some overseas countries than in the UK. Construction and demolition waste can be used as an aggregate in concrete and industrial by-products can be used as alternative binders to cement. Concrete can also be reused when an asphalt surface is required, by using techniques such as crack-and-seat. This maintenance procedure retains the concrete as the load-bearing layer while reducing the incidence of cracking in asphalt overlays that would otherwise result. The crack-and-seat method is currently finding wide application on UK trunk roads and resulting in significant resource and cost savings.

  41.  Standards and techniques exist for recycling "conventional" asphalt pavement materials ("Repave" and "Remix") but their use has been disappointing in an industry that is traditionally risk-averse with respect to new techniques and where the required capital investment is difficult to fund. More recently, TRL, in collaboration with highway authorities and the industry, has published procedures for the use of cold-mix asphalt recycling, which has already been used on a number of Local Authority schemes. Development of complementary procedures is ongoing.

  42.  Within the utilities industry there are increasing environmental and commercial pressures to reduce reinstatement costs. Again, there is potential for re-use of the highway-excavated material. Where materials can be efficiently and economically processed and stockpiled, the re-use of such materials offers significant environmental benefits and inherent cost savings. The re-use of excavated materials, to meet the relevant specifications, has been made possible by the addition of stabilising materials. In the case of water companies the aim is to ensure that industrial by-products are used effectively to stabilise excavated materials such that the resultant material has no adverse effects on water-courses or the environment. Within the utilities companies generally, there is a need to encourage a pro-active culture of sustainable construction to support the conservation of primary aggregates and to promote this through each company's environmental policy. Further laboratory testing and field trials are required to develop mix compositions with the best engineering properties and long-term performance.

  43.  In addition to recycling the existing pavement there is also the potential for the reuse and/or recycling of other materials in asphalt. A recent example is the introduction of 30 per cent green glass cullet into an asphalt product, in place of natural crushed rock. However its use is restricted to structural layers; glass cannot be used in surfacings due to poor skidding resistance. Green glass is a waste material with very limited markets. Tyre rubber has also been used in road surfaces with recent success but there are doubts about its use in structural layers. In depth studies have been undertaken and new specifications will be available, in the near future, for the use of slag by-products, quarry wastes from both slate and china clay sand, and bituminous arisings (planings) in high-quality reuse applications. For surface courses, the use of slag aggregate has been commonplace in proximity to iron and steel works. The geographical range of use has been limited by transport costs; this may change marginally (a further 20 mile radius has been suggested) due to the introduction of the aggregates levy.

  44.  There are other materials where the potential for reuse in the road pavement has not been fully exploited. In particular the use of incineration residue from waste disposal stations (despite the recent case of the Newcastle allotment site), sewage sludge re-use, and demolition debris. The latter has developed as a resource since the introduction of the landfill tax that has led to improved demolition and waste disposal practices.

  45.  As mentioned later in paragraph 50 below, the use of new thin surfacing products has grown enormously over recent years. The specific issue of recycling thin surfacing systems has not yet been addressed, as very few sites have reached the end of their useful life. However, as with their durability, the need to assess their recycling capability is coming to the forefront and studies have been commissioned to research the potential to extend the life of these products.

  46.  Overall, the technology required to enable large increases in recycling is either in place, going through approval procedures, or the subject of current research. To secure these increases, three factors will have to be addressed.

    —  The "newer" sources of "waste" materials as viable pavement materials will have to be validated.

    —  Performance specifications will have to be formulated that will allow contractors more freedom to innovate in the use of materials for road construction and maintenance.

    —  Procurement procedures will need to be developed that encourage the implementation of recycling. These might involve some form of scoring in the assessments of tenders.

Quieter road surfaces

  47.  The first "quieter" road surfacing material was porous asphalt, developed during the 1970s and adopted, after extensive trials, for use on trunk roads in the 1990s. Originally developed for enhanced high-speed wet-friction on airfield runways, it also offers the benefits of low-noise and reduced spray. However, the HA has recently dropped porous asphalt from use due to its high cost and some doubts about guaranteeing durability. Cost considerations have also limited the use of porous asphalt by Local Authorities. Continuing development of this material, for instance in twin-layer systems, where only a thin upper-surface is made from premium aggregate, may prove viable in the future.

  48.  Asphalt thin surfacing products were first developed on the continent and introduced into the UK in the early 1990s. Changes in the material specifications were required to meet the UK's more stringent requirements for skidding resistance and TRL undertook extensive trials of these surfacings, for the HA, before they were permitted for use. The HA encouraged suppliers to develop their own proprietary thin surfacing systems and this led to the development of an approval scheme, operated by TRL and the British Board of Agrément. Approval has been granted for more than 20 products and most other highway authorities have also adopted this scheme.

  49.  These thin surfacing materials are open-graded with a degree of surface porosity, which means that, like porous asphalt, they offer marked noise reductions over conventional materials such as chipped hot-rolled asphalt (HRA). Generally, porous asphalt and thin surfacing give noise reductions equivalent to a reduction in traffic of 50-70 per cent. However, there is recent evidence that this reduction can be significantly diminished on wet roads. No equivalent diminution was found to be the case for non-porous HRA.

  50.  Thin surfacings are now the predominant surface course materials for UK trunk roads and Local Authority principal roads, indeed the HA has recently issued new advice which actively discourages the use of HRA and surface dressing systems as alternatives. However, some issues remain open to question in the, now widespread, use of thin surfacings. Their long-term durability compared to HRA has yet to be proven, due to their recent acceptance, and continued performance monitoring of older sites is being undertaken by TRL for the HA. Another issue concerns the sustainability of these products. Open-graded materials require carefully sized aggregates and do not use the fine fraction of material generated by the production process. These factors are responsible for an increase in unused fine aggregate waste. Also, these systems use premium, skid-resistant aggregate throughout the layer (about 40mm thick) rather than just in the surface, as for HRA or surface dressings. This is a sub-optimal use of a scarce and expensive natural resource. This could be countered to some extent by recycling of the materials after their initial lifetime as discussed earlier.

  51.  A third surfacing offering a quieter road than conventional materials is exposed aggregate, or "whisper", concrete. This surface can provide noise reductions compared to HRA, equivalent to a reduction in traffic of up to 40 per cent. The reduction is much greater compared to traditional concrete surfaces, which have recently become very unpopular amongst neighbouring communities due to high noise levels. Concrete surfaces have potential benefits compared to asphalt, in that, if properly constructed and maintained they will not undergo surface deterioration rutting, which is a recognised risk for asphalt roads. The same comments apply with regard to the use of premium aggregates in depth as for thin surfacings.

  52.  In response to public opinion regarding concrete surfacings, the 10-Year Plan commits the HA to overlaying all concrete stretches with quieter surfaces. The HA will prioritise these works where the noise level from the existing concrete surface affects the most residents. On the grounds of noise level, the justification for overlay of whisper concrete would appear to be weaker than for other concrete roads.


  53.  This memorandum has summarised, necessarily briefly, aspects of maintenance on which research can throw light. The matters discussed are in many cases complex and further more extensive argumentation can be found in relevant technical reports.

TRL Limited

23 February 2001

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