Chapter 4 Road Network
Chapter 4 Road Network
1. Introduction
1.1 This chapter provides information about public road lengths by local authority, road class, type and speed limit. It also includes statistics on the amount of trunk road constructed/re-surfaced and information on the residual life of the trunk road network.
1.2. Unusual year to year changes in the reported road lengths may be due to the gradual introduction of Geographical Information Systems (GIS) to calculate road lengths by the data providers- see section 3.4.
Key Points
- Scotland has 55,906 kms of road network
- Six per cent is trunk road (1% is motorway)
- Scotland has 10.5 kms of road per 1,000 people compared to 6.4 kms in GB.
2. Main Points
Road length
2.1 There were 55,906 kilometres of public road in Scotland at 1 April 2012. The trunk road network accounted for 6% of the total. Other (non-trunk) A roads represented 13% of the total. Minor roads (B and C roads, and unclassified roads) accounted for the remaining 81% of roads. (Table 4.1)
2.2 The motorway network increased by 6% between April 2011 and April 2012. This increase is a result of the opening of the M74 extension in the South of Glasgow in June 2011 and the M80 Stepps Haggs motorway upgrade opening in August 2011. (Table 4.1)
2.3 Over a quarter of the total trunk road network, and about one-seventh of the Scottish road network, is within the area of the Highland Council. Around 10% of the Scottish road network is within the Aberdeenshire Council area and a further 8% is within the Dumfries and Galloway Council area. These three Local Authorities account for a third of Scotland's road network. (Table 4.2)
Road Maintenance
2.4 Overall there was a small decrease (2%) in the amount of trunk road that was newly constructed, reconstructed, strengthened or surface dressed in 2012-13 compared to the previous year. (Table 4.3)
2.5 There were no new trunk roads constructed in 2012-13. (Table 4.3)
2.6 In 2012-13, 28.0% of the motorway network and 9.9% of the dual carriageway trunk road network required close monitoring of the state of the road surface. (Table 4.5 (b))
2.7 In 2012-13 the National Road Condition Indicator (RCI) showed 29% of the local authority A road network may, following more detailed examination, require some kind of maintenance (see section 3.7). For the whole of the local authority network (all road categories), about 37% may similarly require some kind of maintenance. (Table 4.6)
3. Notes and Definitions
3.1 The trunk road network is the responsibility of Scottish Ministers, and comprises all motorways and some of the main A roads (local councils are responsible for non-trunk roads). The Government's view, when it reviewed the trunk road network in 1994, was that the trunk road network should:
- provide the road user with a coherent and continuous system of routes which serve destinations of importance to industry, commerce, agriculture and tourism;
- define nationally important routes which will be developed in line with strategic national transport demands; and
- ensure that those roads which are of predominately local importance are managed locally.
3.2 On 1st April 1996, local government was reorganised, and the 32 present Councils replaced the former Regions, Districts and Island Areas. At the same time, changes were made to the trunk road network: about 580 km of former non-trunk roads became trunk roads, and over 340 km of former trunk roads ceased to be trunk roads.
3.3 Major roads: Motorways and A roads.
3.4 Changes in road lengths: Where there has been a change to the use of a Geographical Information System (GIS) as the basis of the road lengths figures, they may differ significantly from those for the previous year: see section 4.1.3. In 2012 the Trunk road figures were recalculated to include A road slip roads which had been excluded from the totals in previous publications. The time series has been updated to include this data resulting in an increase of 3-4% in Trunk road length and an increase in overall road length of 0.2%. The methodology for calculating the trunk road totals from the database has also changed resulting in some small changes to road lengths from those previously published.
3.5 Operating Units: Since 2001-02, the management and maintenance of the trunk road network has been performed by 4 Operating Companies (South West, North East, South East & North West). Details of the areas covered by these Units can be found in the Annex.
3.6 Trunk road constructed, resurfaced, etc in tables 4.3 and 4.4: Figures up to 1995/96 (which appeared in previous editions) were estimates based on the area that was treated, and an assumed standard lane width of 3.5 metres. From 1996/97 actual figures are produced from the Transport Scotland Trunk Roads Network Management.
3.7 Local authority road network condition
3.7.1 The statutory performance indicator for the condition of the local authority road network is defined as the percentage of the road network, derived from a combination of established condition parameters measured at network level, which should be considered for maintenance treatment, i.e. have reached a condition where more detailed monitoring or investigation is required to establish if and when remedial measures are required.
3.7.2 In 2007-08, the indicator changed from the former Scottish SPI, which included data on longitudinal profile, rutting and texture, to the new UK. Standard Road Condition Indicator (RCI), which in addition includes data on carriageway cracking and takes account of the severity of each defect and its relative importance to road users. Further information about the collection of RCI data can be found at: http://scots.sharepoint.apptix.net/srmcs/General%20Publications/SCANNER_Spec_2011_Volume_1.pdf
3.7.3 Information on the condition of local authority roads is collected in the Scottish Road Maintenance Condition Survey, which is co-ordinated by the Society of Chief Officers of Transportation in Scotland (SCOTS), on behalf of Scottish Local Authorities. The survey is described briefly in section 4.3. As with any survey, the nature of the methods used could lead to apparent minor year-to-year variations.
3.7.3 Where previously, a breach of any single parameter threshold would result in a 10m-section being classified as amber or red; from 2007/08 onwards the new RCI each defect is assigned a score, dependent on its severity and relative importance, and the summation of the individual parameter scores is used to define the section category.
In order to present its results graphically and on maps, the following colour coding has been adopted:
- Green - a score less than 40 - the road is considered to be in an acceptable condition;
- Amber - a score of 40 or greater but less than 100 - further investigation should be taken to establish if treatment is required;
- Red - a score of 100 or greater - the road has deteriorated to the point at which repairs are likely to be required to prolong its future life
3.7.4 The performance indicator covers the amber and red categories, taken together. It represents the percentage of the road network for which some kind of maintenance may be required. It does not take account of the difference in the costs of the treatments which may be required to restore the carriageway to an acceptable standard. The indicator does not currently cover edge deterioration, although it is the intention, subject to further research, to include this.
3.7.5 SCOTS notes that, when examining the results for individual local authorities, it is important to remember that local road networks vary in character, carry different volumes of traffic and serve widely disparate communities. In SCOTS' view, authorities should not be judged on the absolute values of their amber or red proportions in any given year, but on their performance to improve the condition of their road networks.
4. Sources
4.1 Road lengths
4.1.1 Information on road lengths is mainly obtained from annual returns made to the Transport Scotland by Councils and by the trunk road management operators. (The figures for motorways are now prepared by Transport Scotland using a GIS - see section 4.1.4). These returns provide the total lengths of the roads for which the Council or trunk road management operator is responsible. The road lengths are categorised in a number of ways (e.g. by class of road, by type of road and by speed limit).
4.1.2 Because the returns provide only the total lengths of roads of various types (they do not provide any information about any individual roads) they can contain errors which cannot be detected, and, even in cases where an error is suspected, it may not be possible to determine how the figures should be corrected. There are a few cases of apparently unusual changes in the figures between one year and the next, which may be due to errors in the statistical returns (for example, it appears that the figures for dual carriageways may have been affected by the double-counting of some lengths of dual carriageway in some years).
4.1.3 Some councils now calculate their road lengths using GIS, which should reduce the number of errors in the longer term. However, changing to a GIS as the source of the statistics can cause a discontinuity in the figures. They will no longer be affected by any errors inherent in the old method of estimation. There may also be changes in the basis of the figures - for example, in the way in which the lengths of roads at roundabouts are counted. Different methods can give different results: for example, the straight-line distance across a roundabout will differ from the distance around the roundabout; or just half the distance around might be used (to represent the average distance which is travelled on the roundabout).
4.1.4 The effect of a change to a GIS as the source of the data can be seen using the figures for motorways for 2000, which were prepared by the then Scottish Executive using a GIS. The figures for each local authority area (which were published in Table 5.2 of Scottish Transport Statistics no. 20 / 2001 edition) could differ from the figures reported by the trunk road management operators for 1999 (which were published in the previous edition), even in local authority areas where there were no changes to the motorway network between April 1999 and April 2000. The then Scottish Executive derived its figures using particular ways of counting the road lengths for (eg) slip roads and roundabouts. The precise basis of the figures which were reported for earlier years is not known.
4.1.5 The change to the use of a GIS was also the reason why the length of unclassified roads reported by Falkirk Council increased from 400 km in 1999 to 572 km in 2000. In such a case, it must be assumed that the figures produced by the use of the new system are more reliable than those which had been provided previously.
4.2 Trunk road network - residual life
4.2.1 The physical condition of Motorways and trunk roads is monitored by annual condition surveys which are undertaken for Transport Scotland by specialist contractors. The surveys are designed to provide information about the structural, surface and safety condition of the road surface (which are referred to as pavements by the engineers). Road condition data is measured by a slow moving vehicle that tests the structural strength by pushing a weight onto the road and measuring how much it deflects. This is then analysed to assess how much life is left in the road pavement. A road network cannot be kept in perfect condition: there will always be some wear and tear, and it is most economic to replace a worn out carriageway at the end of its useful life. When there is no life (which is counted in the residual life <0 column in Table 4.5), the road requires close monitoring to ensure its overall condition does not deteriorate significantly before it is replaced. The data from the surveys is processed annually in a Pavement Management system so as to identify objectively performance and to target the available funds on those areas of greatest need.
4.2.2 The base network includes most motorways and dual carriageway trunk roads. The surveyed network also includes some single carriageway trunk roads. The surveyed network figures are on a cumulative basis - for example, the figure for 2002-03 represents the combination of the condition in 2002-03 of the roads which were surveyed in 2002-03, the condition in 2001-02 of the roads which were surveyed most recently in 2001-02, and so on. Therefore, the surveyed network figures do not represent the current position in each of the specified years: there may have been some improvement or deterioration in the condition of some of the roads since they were surveyed in earlier years. In addition, as the coverage of the surveyed network expands, it includes further roads, whose condition may differ significantly from that of the roads that were already in the surveyed network. Therefore, some of the apparent changes in the figures between years may be due to the expansion of the surveyed network.
4.3 Local authority road network condition - the Scottish Road Maintenance Condition Survey
4.3.1 The Scottish Road Maintenance Condition Survey, which is organised by the Society of Chief Officers of Transportation in Scotland (SCOTS) on behalf of Local Authorities, is carried out by a specialist contractor using vehicles accredited annually by the TRL. TRL also undertakes quality assurance checks throughout the year. The vehicles are equipped with lasers and high resolution cameras, to collect data for processing by computer and currently record:-
- The road geometry (gradient and shape);
- Variations in the longitudinal profile (evenness of ride along the road);
- Transverse profile variance (deformation across the road )
- Wheel track rutting / deformation in the wheel path ;
- The presence of cracking within the carriageway;
- Texture (roughness of the surface of the road).
- The extent of edge deterioration (due to over-riding or lack of lateral support)
As indicated previously in section 3.7, the construction of the Scottish road performance indicator was changed in 2007-08 to the new UK Standard Road Condition Indicator (RCI), with each ten metre stretch of road being assigned to one of three categories (Green, Amber or Red) depending on the overall defect score.
4.3.2 The survey currently aims to cover all local authority A roads in both directions every two years, all B and C roads in both directions every four years, and a 10% sample of unclassified roads in one direction each year. In order to minimise the effect of sampling errors on the result, the RCI for unclassified roads is calculated from four years data, as agreed with Audit Scotland and is in effect a rolling four-year indicator. While the survey machines have been calibrated and shown to provide consistent results, variations can occur due to minor differences in machine settings or in the path followed by the survey vehicle (which may well be dictated by, for example, the presence of other vehicles on particular parts of the road).
4.3.3 The SRMCS survey started in the 2002-03 financial year, when it covered all A roads in all local authorities plus a sample of the B, C and unclassified roads in some local authority areas. 2003-04 was the first year for which the survey covers a sample of all road categories in all local authority areas, and is therefore the first year for which results can be produced for Scotland as a whole.
5. Further Information
5.1 Information on GB road network statistics can be found in the Department for Transport annual publications Road Traffic Statistics and Transport Statistics Great Britain.
5.2 Further information on road lengths in Scotland is available from Transport Scotland's Trunk Road Network Management, contact Stuart Hay (tel: 0141 300 8282).
5.3 Further information on the construction of Scotland's trunk road network, is available from Allan Roberts of Transport Scotland's Trunk Road Infrastructure and Professional Services (tel: 0141 272 7211).
5.4 Further information on the maintenance and the condition of Scotland's trunk road network, is available from David Arran of Transport Scotland Road Trunk Roads Network Management (tel: 0141 272 7370).
5.5 Further information on the Scottish Road Maintenance Condition Survey of the local authority road network, conducted on behalf of Councils by the Society of Chief Officers of Transportation in Scotland, is available from Graeme Ferguson, Project Manager (gferguson@pkc.gov.uk) or at www.scotsnet.org.uk .
6. Other data sources
Within Scottish Transport Statistics:
Chapter 5 - Road Traffic
Chapter 12 - international Comparisons.
Department for Transport produce a range of statistics on the GB network as referred to above and Eurostat compile road length statistics for EU countries, including a split by road type. See chapter 12 for more detail.
Source: Transport Scotland - Not National Statistics
1. Motorway road lengths are derived from GIS from 2000 onwards - see commentary for more details.
2. Road lengths are physical length rather than carriageway length e.g. 10km of dual carriageway counts as 10km, not 20km.
3. These figures now include A road slip roads which have been excluded from the figures in previous publications. The time series has been updated to include this data resulting in an increase of 3-4% in Trunk road length and an increase in overall road length of 0.2%. The methodology for calculating the trunk road totals from the database has also changed resulting in some small changes to road lengths from those previously published.
4.Trunk road lengths for these roads have now been derived more accurately using a GIS system from 2006.
5. For 2008 and 2009 single and dual carriageways figures are estimated.
6. As at 10 October 2013.
Source: Transport Scotland - Not National Statistics
1. Motorway road lengths have been consolidated using a GIS system which means that there will be some changes to previously published figures.
2. Triangulation with other sources of road length data has occurred to improve the quality of the information. Figures may not be comparable with previous editions.
3. As at 10 October 2013.
4. The drop in the length of trunk A roads from last year is probably due to the detrunking of A80 with the opening of the M80.
Source: Transport Scotland - Not National Statistics
1. Due to completion of the M74 and the M80 Stepps to Haggs there have been large increases in the amount of construction in the SE and SW and 50 km of reconstruction in the SE.
Source: Transport Scotland - Not National Statistics
Source: Transport Scotland - Not National Statistics
Table 4.5 Trunk road network: Residual Life1 (years)
| Residual Life (years) | ||||||
|---|---|---|---|---|---|---|
| <0 | 0-4 | 5-9 | 10-14 | 15-19 | >19 | |
| percentages | ||||||
| 1997-98 | 11 | 8 | 11 | 8 | 8 | 54 |
| 1998-99 | 10 | 9 | 9 | 8 | 7 | 57 |
| 1999-00 | 10 | 8 | 10 | 9 | 10 | 53 |
| 2000-01 | 9 | 7 | 9 | 8 | 8 | 59 |
| 2001-02 | 4 | 4 | 7 | 7 | 10 | 68 |
| 2002-03 | 4 | 4 | 7 | 7 | 11 | 67 |
| 2003-04 | 4 | 4 | 6 | 7 | 12 | 67 |
| 2004-05 | 4 | 5 | 6 | 7 | 13 | 65 |
| 2005-06 | 4 | 4 | 6 | 7 | 15 | 63 |
| 2006-07 | 5 | 4 | 6 | 7 | 15 | 63 |
| 2007-08 | 4 | 4 | 7 | 7 | 13 | 65 |
| 2008-09 | 4 | 4 | 6 | 7 | 11 | 68 |
| 2009-10 | 5 | 5 | 7 | 8 | 11 | 64 |
| 2010-11 | 5 | 4 | 6 | 7 | 9 | 69 |
| 2011-12 | 10 | 7 | 10 | 10 | 11 | 52 |
| 2012-13 | 16 | 9 | 11 | 9 | 11 | 44 |
Source: Transport Scotland - Not National Statistics
Source: Transport Scotland - Not National Statistics
1. Residual life represents the number of years to elapse before the pavement reaches the stage when it may be necessary to undertake relatively more expensive reconstruction rather than strengthening to restore its full life.
2. The part of the network that requires close monitoring is that which has a residual life of less than zero.
Note: it has been decided that surveyed network length is not required as the figures produced are now representative of the whole network as shown in Table 4.1
3. These figures are provisional.
Source: Scottish Road Maintenance Condition Survey - Not National Statistics
1. From 2007-08 the basis of the statutory road performance indicator in Scotland changed to the UK Standard RCI. More detailed information on the changes can be found at the following web link http://scots.sharepoint.apptix.net/srmcs/General%20Publications/SCANNER_Spec_2011_Volume_1.pdf
2. While it has been possible, following the change to the indicator, to calculate the equivalent RCI value for all classified roads from 2005-06, it has not been possible to do this in a reliable manner for unclassified roads, owing to a lack of cracking data for those years. As unclassified roads represent a significant part of the total road network, RCI data for the network is similarly not available for this period It is important to note that owing to the different formulation, no valid comparison can or should be made between the two series
3. The categories used to indicate the condition of the road are described in Section 3.7 of the text. In brief:
amber - further investigation should be undertaken to establish if treatment is required
red - the road has deteriorated to the point at which it is likely repairs to prolong its future life should be undertaken.
4. Information for 2002-03 is available only for A roads - see Section 4.3 of the text.
5. The SPI figures for Scotland in 2004-05 exclude Glasgow, as the survey in Glasgow was undertaken on a different basis in that year.