I receive a lot of enquiries from constituents asking about how roads maintenance is prioritised and what methods are used. The text below is a briefing from Council Officers on the matter.
Roads Asset Management
The Roads Asset Management Plan (RAMP) is an integral part of the new investment strategy for carriageways and footways. It will be used to balance the long-term capital renewal needs for our network, with the short term need for revenue repair road works, in order to keep the city’s roads well maintained.
The RAMP will drive the improvement programme for all aspects of management of the carriageway and footway network including:
- Developing knowledge of new materials and maintenance techniques;• Suitability for use on Edinburgh’s network;
- Benchmarking against other local authorities to identify improvements to current practices;
- Targeting investment to ensure best value and improved lifecycles; and,
- Critically reviewing the performance of current and future investment.
Carriageway and Footway Investment Strategy
The condition of Edinburgh’s roads is assessed annually as part of the Scottish Roads Maintenance Condition Survey (SRMCS), an independent survey of road conditions in all 32 Scottish local authorities. The survey provides each local authority with a Road Condition Index (RCI) which identifies the percentage of roads that should be considered for investment. Edinburgh’s most recent RCI is 34.6%, based on the SRMCS from 2015/16, placing Edinburgh 16th out of the 32 Scottish local authorities.
In 2005/06 capital investment in roads increased from just over £3m per annum to over £16m, increasing to £20m in 2008/09 and to 24.5m in 2013/14. Although the increase in the capital budget saw a significant initial improvement in the condition of Edinburgh’s roads, performance has remained fairly static for the last 6 years, despite sustained levels of investment.
The RCI consists of three categories of deterioration: Red, Amber 1 and Amber 2, with roads in the red category being in the worst condition. Up to 2015/16, the majority of carriageways prioritised for investment fell within the red category. Treating the Red category roads only resulted in a small number of carriageway resurfacing or strengthening schemes being carried out each year, due to the cost of these treatments.
As part of the development of the Roads Asset Management Plan (RAMP), analysis was carried out on the impact on Edinburgh’s RCI if the Council had continued with the existing approach to roads capital investment. The chart below shows the effect of the previous investment strategy on the percentage of Edinburgh roads falling into the red and amber categories of deterioration (i.e. in need of maintenance investment), over a 20-year period, assuming that capital investment remained at 2015/16 levels. By year 20, the percentage of roads requiring maintenance would increase from just under 35% to nearly 60% while the percentage that fell into the red category rises from 5% to over 10%.
Despite the relatively high levels of capital investment, there would have been insufficient resource to treat all the roads in the red category. Furthermore, because investment was Localities ‘Surface Enhancement’ works) there was almost no investment going into treating roads in the amber categories, which over time will continue to deteriorate and eventually slip into the red condition category.
Consequently, modelling work was carried out using the Roads Assent Management Plan, in order to create an investment strategy that would improve the condition of Edinburgh’s carriageway and footway network.
As part of this modelling work for the RAMP, alternative scenarios for capital investment were developed. These scenarios were predicated on a more preventative approach aimed at roads that are in the amber condition categories. Investment interventions on these roads require less expensive treatments (e.g. surface dressing, slurry sealing) which improve the condition of the carriageway or footway, extend the design life before resurfacing, strengthening or reconstruction is required. Due to the lower cost of the treatments required on amber condition roads, more can be treated each year. Roads in the red category will continue to be treated each financial year but fewer than in previous years. Once deterioration has reduced throughout the network, more investment can then be diverted back to red category roads. The chart below illustrates the impact of this preventative approach over 20 years, assuming levels of capital investment remain at current levels.
As part of the work carried out on the investment strategy, surfacing treatments were re-introduced in Edinburgh, treating roads in the amber categories, and local footways in 2016/17. These treatments are currently used throughout Scotland.
Surface dressing is a process that provides added protection to the carriageway surface, sealing it from the ingress of water while also enhancing its skid resistance. It is a preventative treatment and can extend the useful life of a road by around 10-15 years.The process entails spraying the road with bitumen and covering it with stone chippings. The dressing is then rolled, which together with the actions of slow moving traffic, embeds the stone chips into the surface.
Micro Asphalt (also referred to as ‘micro surfacing’, ‘micro’ or ‘thin surfacing’) is a surface treatment for roads; one which is laid over the top of the existing surface to seal and protect it. It consists of a water- based mix of stones and bitumen which is spread over the existing surface by a special machine. It is a preventative treatment and can extend the useful life of a road by around 10-15 years.It can be used when surface dressing is not suitable. It reduces road noise and can rapidly transform a road with extensive patching and utilities reinstatements into one with minimum surface irregularities.
Footway Slurry Sealing
Slurry sealing is used to repair imperfections and to seal footway surfaces from the ingress of water to the underlying foundations. It is a preventative treatment which is to be used to extend the useful life of a footway, thereby delaying more significant and costly treatments. It is a semi self-levelling system and is spread by hand using squeegees on top of the existing footway surface. It is expected to provide an even and consistent surface free from trip hazards. It is a preventative treatment and can extend the useful life of a footway by around 7-10 years.Slurry sealing is generally laid to a nominal depth of 6mm but it can also be laid up to 10mm thick where undulations in the existing surface are more pronounced. The process is substantially faster than traditional footway surfacing methods, thus reducing the disruptive impact on residents and businesses.