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1. Introduction
1.1 This chapter provides information about road traffic on major roads, such as the total volume of traffic by type of road and type of vehicle, the volume of traffic on major roads by council area, and some figures on traffic flows at selected points on the road network.
1.2 The main changes in this edition are as follows:
2. Main Points
2.1 The estimated total volume of traffic on Scotland's roads in 2000 was about 43.2 billion (thousand million) vehicle kilometres: apparently 0.3% less than in 1999. Traffic in 2000 was affected by the fuel protests in September. DTLR's assessment is that the effects of the protests caused the total volume of traffic, for GB as a whole, to be about 0.4% lower in 2000 than it would otherwise have been. If one assumes that the fuel protests had the same percentage effect on traffic in Scotland as in GB as a whole, it appears that there would have been a 0.1% rise in traffic in Scotland in 2000, had there been no fuel protests.
2.2 When using the traffic estimates, it must be remembered that they indicate only the broad level of traffic, and may be unable to provide reliable information about year-to-year changes. This is because (as is explained in the "Sources" section) they are based on information from a very small cross-section of the roads in Scotland: "12 hours in one day" traffic counts taken at around 500 sites per year and data from automatic traffic counters at fewer than 100 sites. This limits their precision. For example, last year's estimate of the total volume of traffic in 1999 was 43.0 billion vehicle-kilometres. Since then, more information for 1999 has become available for use in the calculations, and the method of producing the estimates has been improved. This year's estimate for 1999 is 43.3 billion. The size of the revision (0.3 billion vehicle-kilometres) indicates that there is some uncertainty in the estimates. The estimate for traffic on major roads in 2000 is 25.2 billion, which is below the revised estimate for 1999 (25.4 billion), but the apparent fall is not great in the context of the uncertainty of the estimates (the original estimate for 1999 was 25.1 billion) and the likely scale of the effect of the fuel protests. As the estimates for the five years from 1996 to 2000 have fluctuated between roughly 24.5 and 25.6 billion vehicle kilometres per year, it appears that the total volume of traffic on major roads has remained broadly unchanged between 1996 and 2000. However, the longer-term picture is different: the estimated total volume of traffic on major roads has grown by about 16% since 1990. (The apparent fall between 1995 and 1996 is thought to be due to the effect of local government reorganisation on the method of estimating traffic volumes - see section 4.3 below). Traffic on Motorways has risen faster - by 62% since 1990. (Table 6.1)
2.3 In 2000, traffic on Motorways totalled an estimated 5.3 billion vehicle kilometres (12% of all traffic). This was less than the estimated 8.8 billion vehicle kilometres on trunk A roads (20% of the total), and the 11.1 billion on non-trunk A roads (26%). Most of the total traffic on A roads was on roads with speed limits of over 40 mph (which are sometimes referred to as "non built up" roads), which accounted for 14.9 billion out of the A roads total of 19.9 billion vehicle kilometres. (Table 6.1)
2.4 Minor roads (B, C and unclassified roads) account for the remaining 42% of traffic: an estimated 18.0 billion vehicle kilometres in 2000, most of which was on unclassified roads (9.9 billion). Over two-thirds of minor road traffic (12.3 billion vehicle-kilometres in 2000) is on roads with a speed limit of 40 mph or less (sometimes referred to as "built up" roads). As is explained in section 3.2, reliable estimates of the volume of traffic on minor roads in Scotland are not available prior to 1998. (Table 6.1)
2.5 The apparent large changes between 1998 and 1999 in the figures for "built up" and "non built up" major roads are due to the introduction of an improved method of estimation and to the use of a better source of data on road lengths - see section 4.2 below. (Table 6.1)
2.6 Since 1990, the volume of car traffic on major roads has increased, as has the volume of light goods vehicle traffic. As is explained in section 3.4, the apparent fall in the volume of heavy goods vehicle traffic on major roads is due to the clarification of the definition of one of the types of HGV for the traffic counts: in earlier years, vans were wrongly counted as HGVs. (Table 6.2)
2.7 Cars account for four-fifths of the total volume of traffic on the roads (major and minor roads combined), and light goods vehicles for 11%. Heavy goods vehicles contribute under 6%. (Table 6.3)
2.8 Because the introduction of an improved method of estimation and the use of a better source of data on road lengths (see section 4.2 below) affected the figures for individual Council areas, the revised estimates for 1999 are given in Table 6.4(a).
2.9 In 2000, over a fifth of motorway traffic is within the City of Glasgow, and Highland is the Council area with the greatest total volume of trunk A road traffic (measured in vehicle kilometres). (Table 6.4(b))
2.10 The monthly average daily traffic flows recorded at a selection of Automated Traffic Classifier (ATC) sites are given in Table 6.5. The levels of traffic varied greatly. Taking the total of traffic in both directions, the average flow at the M8 Harthill site was lowest in December (averaging about 44,000 vehicles per day) and highest in August (averaging over 53,000 vehicles per day). On the A720 Edinburgh City bypass at Dreghorn, average daily flows varied between just under 50,000 in August and almost 70,000 in March. In contrast, the average daily flow at the A920 Huntly site was less than 2,000 vehicles in every month. Traffic levels can also vary considerably within the year: for example, the A82 Spean Bridge ATC site in August averaged 6,900 vehicles per day - almost two and a half times the average of 2,900 in January. (Table 6.5)
2.11 A range of information about traffic flows at selected points on the trunk road network is given in Table 6.6. Of the sites listed, the M8 Kingston Bridge was the busiest, with an annual average of over 145,000 vehicles per day in 1999. Its Monday-Friday average was over 155,000 vehicles per day, and its Monday-Friday peak hour average flows were almost 12,500 vehicles in the morning and about 10,500 vehicles in the evening. At the opposite end of the scale, a point on the A9 between Inverness and Wick averaged roughly 1,600 vehicles per day over the year as a whole (2,300 in August: figures are also given for that month to show any effects of the tourist season), and average "peak hour" flows of around 150 vehicles. The A75 between Gretna and Dumfries had, of the sites listed, the highest percentage of traffic accounted for by heavy goods vehicles: in 1999, 23% of vehicles on that road were HGVs (27% on weekdays). (Table 6.6)
2.12 At the selected monitoring sites, carbon monoxide concentrations have been below the level of the air quality strategy objective since 1992, and the lead concentrations have been below the value set as the objective for 2008 since 1989. However, nitrogen dioxide concentrations at both the Edinburgh and Glasgow monitoring sites have, for the same period, been above the level set as an objective for December 2005. The air quality strategy objective for ground level ozone states that by 2005 the maximum daily concentrations should not exceed 100 m g/m3 on more than ten days per year. While, ozone concentrations at the selected monitoring sites have fluctuated over the years, the target value was exceeded on more than ten days a year at the two rural sites in 1999 (Eskdalemuir and Strath Vaich) in most of the years since 1989. (Table 6.7)
2.13 The overall total amount of petrol and diesel delivered in Scotland has not changed much in the past ten years: it was 2.57 million tonnes in 1989, rose to 2.76 million tonnes in 1992 then declined to 2.57 million tonnes in 1999. However, there have been some large changes within that overall total. Deliveries of leaded petrol fell sharply from about 1.38 million tonnes in 1989 to only 120,000 tonnes in 1999. Over the same period, deliveries of unleaded petrol grew very rapidly from around 340,000 tonnes in 1989 to 1.27 million tonnes in 1999. Overall, the total amount of petrol delivered declined by 18% from 1.72 million tonnes in 1989 to 1.39 million tonnes in 1999: a drop of almost 330,000 tonnes. At the same time, there was a 39% increase in deliveries of diesel, from about 840,000 tonnes in 1989 to 1.17 million tonnes in 1999: a rise of around 330,000 tonnes. Therefore the overall total of petrol plus diesel hardly changed over the period. (Table 6.8)
Notes and Definitions
3.1 The methods that have been used to estimate the volume of traffic on major roads (Motorways and A roads) in Scotland have changed over the years. Section 4 describes the method which is currently used, and then indicates how the methods which were used previously differed from the current method.
3.2 Estimates of the volume of traffic on minor roads (B roads, C roads and unclassified roads) in Scotland that are suitable for publication are only available from 1998. The Department for Transport, Local Government and the Regions (DTLR) estimates the volume of traffic on minor roads using information from traffic counts taken at a selection of sites. The sample of sites and the method of estimation were originally designed solely for the purpose of producing estimates for GB as a whole and, for many years, the Scottish component was not suitable to be the basis of reliable estimates of minor road traffic for Scotland. However, as a result of improvements made by the then Department of the Environment, Transport and the Regions (DETR), estimates of minor road traffic for Scotland as a whole for 1998 onwards can be published. Section 4 describes the methods used.
3.3 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: some former non-trunk roads became trunk roads, and some former trunk roads ceased to be trunk roads. This affected the calculation of the traffic estimates, as is described in Section 4.2. The apparent fall in the estimate of the total traffic volume for major roads between 1995 and 1996 is assumed to be due to the discontinuities caused by the above factors: in effect, the figures for 1995 and 1996 are on different bases, and are not directly comparable.
3.4. There is a discontinuity in the figures for light goods vehicles and heavy goods vehicles between 1997 and 1998. The then DETR clarified the definition of one of the types of HGV for the traffic counts in 1999. Analysis of the data showed that counts in earlier years had included some light vans as if they were HGVs. Therefore, earlier years' figures over-estimated the volume of HGV traffic, and under-estimated the amount of light goods van traffic. When revising the estimates for 1998, DETR adjusted them to put them onto the new basis.
3.5. In 2001, DTLR improved the method of estimating the traffic volumes on major roads with effect from the production of revised traffic estimates for 1999. The new method uses a different source of data on road lengths. The changes in the method and the underlying data had little effect on the estimated overall total for Scotland as a whole. However, the results were a much lower estimate of the total volume of traffic on "built up" major roads in 1999, and a much higher estimate of the total for "non-built up" major roads in 1999, than the previous method had produced for 1999. There were also some large percentage differences in the original and revised estimates for 1999 for some Councils. Therefore, many of the figures given here for 1999 and 2000 are on a different basis from, and so are not directly comparable with, the figures for 1998 and earlier years (and the figures for 1999 published in the previous edition). Section 4 describes the change.
3.6. The average daily traffic flows at Automated Traffic Classifier Sites are "total past the point" figures: traffic is counted in both directions. The estimated traffic flows are based on 7-day averages which include both weekdays and weekends. On occasion, the ATCS counters are not in operation for enough of the month to provide a reliable estimate: in these cases, ".." is used to indicate that no estimate is available.
3.7 The atmospheric pollutants listed in Table 6.7 have been selected because they are considered to be a threat to human health, and transport is understood to be a significant contributor to emissions of the pollutants. In January 2000, the Scottish Executive, UK Government and the other devolved administrations published a new Air Quality Strategy containing air quality objectives for eight pollutants (benzene, carbon monoxide, lead, nitrogen dioxide, ozone, particulates (PM10), sulphur dioxide and 1,3-butadiene). The objectives are policy targets expressed as a maximum ambient concentration to be achieved, either without exception or with a permitted number of exceedences, within a specified timescale. The following table sets out the agreed air quality objectives for the first six of these (the ones to which transport is understood to contribute significantly).
3.8 Carbon monoxide produced from road transport, particularly petrol-fuelled vehicles, accounted for almost 75% of UK emissions in 1998. Emissions have been declining and this is attributed to the installation of catalytic converters in vehicles. Additives in petrol have been the primary source of atmospheric lead. Significant reductions in urban lead levels have occurred since the introduction of unleaded fuel in 1986. The general sale of leaded petrol was banned in the UK from 1 January 2000. All combustion processes in air produce oxides of nitrogen (NOx). Road transport accounts for about half of all NOx emissions in the UK; this contribution is greatly increased in urban areas. The greatest source of PM10 (particulate pollution less than 10m m in diameter) is combustion. In particular, this includes fuel from road transport, which accounts for around 25% of UK emissions of PM10 . Ozone is not emitted directly from any man-made source in significant quantities but arises from the chemical reaction of other pollutants such as NOx and volatile organic compounds produced by road transport, industrial processes and solvent uses. Benzene is a recognised genotoxic human carcinogen and in the UK the main atmospheric source is the combustion and distribution of petrol. Road transport accounts for about 65% of UK benzene emissions.
NATIONAL AIR QUALITY OBJECTIVES
|
Pollutant |
Objective |
Date to be achieved by | |
|
Concentration |
Measured as: | ||
|
Benzene |
16.25µg/m3 |
running annual mean |
31 Dec 2003 |
|
Carbon monoxide |
11.6mg/m3 |
running 8hr mean |
31 Dec 2003 |
|
Lead |
0.5µg/m3 (500ng/m3) |
annual mean |
31 Dec 2004 |
|
Nitrogen dioxide2 |
40µg/m3 |
annual mean |
31 Dec 2005 |
|
Particles (PM10)3 |
40µg/m3 |
annual mean |
31 Dec 2004 |
|
Ozone |
100µg/m3 |
Daily maximum (measured as an 8 hour running mean) not to be exceeded more than 10 times a year |
31 Dec 2005 |
4. Sources
4.1 The method of estimating the total traffic volumes for major roads - with effect from the revised estimates for 1999
4.1.1 Estimates of traffic volumes on major roads (Motorways and A roads) in Scotland by road type, vehicle type, and area within Scotland were produced by DTLR (in earlier years, DETR) in conjunction with the Scottish Executive Road Network Management and Maintenance Division (SE RNMMD) and, in earlier years, the National Roads Directorate of The Scottish Office (SO NRD).
4.1.2 The method of estimation has two main stages. First, traffic flows (which represent the numbers of vehicles flowing past particular points in a specified period) are estimated for approximately 1,900 individual road "links" on trunk and principal roads in Scotland. (A link is normally a section of road between two major intersections). The estimates of the traffic flows on these road "links" are then combined with information about the lengths of roads of the relevant types, to derive total traffic volume estimates (measured in millions of vehicle kilometres) for major roads by road type, vehicle type and Council area. The type of a road is determined by its class (Motorway or A road), by whether or not it is a trunk road (trunk roads are those roads for whose upkeep Scottish Ministers are responsible), and by whether or not it is in a "built-up area" (roads in built-up areas have speed limits of 40 mph or less). The steps involved in each of these stages are described in subsequent paragraphs.
4.1.3 The estimates of traffic flows for the individual major road "links" for each year are derived by a methodology which involves the use of two different types of traffic counts: "link" and "core":
i. The road "link" traffic counts are taken manually, for 12 hours in one day, on a rotating basis (on average about once every six years), at each of the approximately 1,900 road links covering nearly all of the major road network in Scotland. These counts take place in "neutral weeks" during late March, April, May, June, September and October (the aim is to avoid counting, for example, during school holidays, and so to obtain counts which are representative of the level of traffic on each link). Roughly one sixth of all the road links on the major road network are counted each year in Scotland (compared with about 40% in England and Wales). At one time, the aim was to count each Scottish site once every six years. However, in 1999, the then DETR changed the counting schedule in order to improve the accuracy of the estimates: now, the more important links in Scotland should be counted more often, and the less important should be counted less often. Such "12 hours in one day" counts must be scaled up to estimate the total flow of traffic for the year as a whole, and in order to reflect changes in traffic levels in the years after each count was taken. The "core" counters provide the information that is used in the scaling.
ii. The "core" counters which are used are the SE RNMMD's automatic traffic classifiers, which are located at selected sites on major roads through Scotland. These operate, on the whole, continuously: 24 hours per day, throughout the year, and provide information about traffic flows classified by category of vehicle according to their length and number of axles. Most of the "core" counters are situated primarily to provide information to support the management of the trunk road network, but there are some whose purpose is solely to collect data used for the production of the traffic estimates: their locations were chosen by DETR statisticians so that all the "core" counters, taken together, cover a good cross-section of types of road. There are currently about 68 "core" counters in Scotland, but technical problems may prevent some of them from collecting sufficient information in some years. For example, for the 1995 estimates, information from 54 "core" counters was used: 9 on Motorways, 26 on trunk A roads and 19 on local authority A roads.
4.1.4 The estimated traffic flows for each major road "link" for the latest year are then derived by a series of calculations of which the following provides only a broad outline. The "core" traffic counters are used to derive two sets of factors, which are then applied to each of the 1,900 "link" counts:
a. "Expansion Factors" for road type and vehicle type are used
to scale the single day 12 hour "link" counts to provide estimated
traffic flows for the whole year in which the counts were taken.
b. "Growth Factors" for each road and vehicle type are used to scale
estimated traffic flows in the previous year forward to the latest year, for
those links which were not counted in the latest year.
4.1.5 DTLR then estimates the total traffic volume (in vehicle-kilometres) on each major road link by multiplying together the estimated traffic flow for the link and the length of the link. DTLR obtains the length of each major road link, and identifies the Council(s) in which it is located, using a Geographic Information System (GIS). When a link lies completely within the area of one Council, its estimated traffic volume is counted wholly against that Council. In a case where a link crosses a boundary between Councils, its traffic volume is (in effect) split between the Councils pro rata to the lengths of the parts of the link which are in each local authority. DTLR obtains the length of each part of the link which is in each Council's area from the GIS. Splitting the estimated traffic volume for a link pro rata to the lengths of the parts involves an implicit assumption that each part of the link has the same average traffic flow as the part on which the traffic count was taken. This assumption is reasonable, because a link is defined as a section of road between major intersections, and so the traffic flow should not vary much along its length.
4.1.6 These calculations produce estimates of traffic volumes for each road link (or part of a road link) which is within the area of each Council. The estimated traffic volume for each Council is then obtained by adding up the estimates for the relevant links (or parts of links), and the estimates for Scotland as a whole are then produced by adding up the estimates for each Council.
4.2. The change from the method that was used to produce the estimates for 1998 and earlier years, and the resulting discontinuity in figures for some Councils
4.2.1 The method that was used to produce the estimates for 1998 and earlier years differed significantly, in one respect, from the current method. For 1998 and earlier years, DETR did not calculate the traffic volume for each link (or part of a link) using GIS-based information about the lengths and locations of individual major road links. Instead, DETR used information about the total length of roads of each type in each Council's area, which was obtained from the road lengths returns (see Chapter 5; the lengths of Motorway slip roads were excluded from the calculations). The calculations described below were performed for each road type, for the area of each Council.
4.2.2 DETR first calculated the average traffic flow for each road type and area for the latest year by weighting the estimated traffic flow for each individual road link of that road type in that area (calculated as described above) by the total length of the link (as supplied to DETR by SO NRD). Not having the GIS-based information required to split links which crossed boundaries, DETR counted each link as being in the Council which included the location at which the link's traffic count was taken. Therefore, each link contributed to the estimated average traffic flow for only one Council.
4.2.3 DETR then estimated the total traffic volume (vehicle kilometres) for each type of road in an area by multiplying the estimated average traffic flow for the road type and area (calculated as described above) by the total length of roads of that type in that area (as had been reported in the road length returns). The figures for the total road lengths for each area took proper account of links which crossed boundaries, because the people making the returns had to include only the length of each link that was within an area in the calculation of the total road length for that area. Therefore, the figures for an area's total road lengths could cover a somewhat different road network from that used to estimate its average flows (remember that the latter were calculated using data for only those road links for which the locations of their traffic counts were within the area).
4.2.4 It follows that old method of estimation was likely to be less precise than that used to produce the revised estimates for 1999, and the estimates for later years. For example, suppose that there were only two major road links in a particular Council: a short low-flow link whose traffic count was taken at a point within the Council, and a long high-flow link, which crosses the boundary into another local authority, whose traffic count was taken at a point in the other area. Using the old method of estimation, the average traffic flow for the Council would be calculated using only the data for the low-flow link, and then multiplied by the total road length for the Council (including the length of the part of the high flow link that was within its boundaries). The total traffic volume for the Council would therefore be under-estimated: the method could not take account of the high traffic flow on the long link, because its traffic count took place in another local authority. So, the introduction of the improved method will cause a discontinuity in the series of figures for the Council.
4.2.5 As indicated earlier, the change in the method introduced a new source of information about road lengths. Therefore, there may be cases where the total for a Council of the lengths of the road links of a particular type that DTLR obtains from the GIS differs somewhat from the total road length of that type shown in the relevant road length return. There may also be cases where the length of a road link that DTLR obtains from the GIS differs from the length of that link that would be reported by SO NRD. Such differences would cause further discontinuities in the series of figures for individual Councils. In addition, the new method may record more precisely than hitherto the lengths of the parts of each road link that are classified as "built up" and as "non built up". Previously, some road links which had both "built up" and "non built up" stretches (such as a road link between a point which is within a built up area on the outskirts of a city or town and a major junction in a rural area) may have been counted as if they were wholly "built up", and others counted as if they were wholly "non built up". As a result, the traffic on such a link would have contributed to the average for only one type of road, and the length of such a link would have contributed to the total length of only one type of road, for the relevant area. If those links which had both "built up" and "non built up" stretches were disproportionately more often counted as wholly "built up" than as wholly "non built up", the result would have been that the previous method of estimation would have over-estimated the volume of traffic on "built up" roads and under-estimate the total volume of traffic on "non built up" roads. In consequence, the introduction of the improved method of estimation would lead to a fall in the estimates for "built up" roads and an increase in the estimates for "non built up" roads.
4.2.6 The estimates for 1999 that appeared in "Scottish Transport Statistics no 19 / 2000 edition" were produced using the old method. Because of the effect of the change in the method, DTLR produced revised estimates for 1999 using the new method, which are published in this edition of "Scottish Transport Statistics". Comparing these with the old estimates for 1999 will reveal some large percentage differences in the figures for some types of road and for some Councils. Therefore, considerable care must be taken when making any comparisons of the figures for areas within Scotland, and for "built up" and "non built up" roads, before and after 1999, because of the effect of the change in the method of estimation: in many cases, the figures for the period up to 1998 (and the original estimates for 1999) are not directly comparable with the figures for 1999 (revised) and later years, being effectively on different bases.
4.3 The discontinuity in the estimates between 1995 and 1996
4.3.1 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: some former non-trunk roads became trunk roads, and some former trunk roads ceased to be trunk roads. This affected the calculation of the traffic estimates in two ways:
a. the areas that were used in the calculations changed, from Regions/Islands to Councils. This introduced a discontinuity. The then method of estimation (described above) multiplies the average traffic flows (for those "links" for which figures are available) for each type of road in an area by the total lengths of road of the same type in that area. It can be demonstrated that the result of such calculations for a Region as a whole may well differ from the result of performing the calculations for each of the relevant Councils separately, and then adding up the results. Therefore, the change in the kind of area used in the calculations introduced a discontinuity into the results.
b. the re-classification of some trunk roads as non-trunk roads, and vice versa, meant that the total lengths of certain types of road changed in some areas. In addition, some "links" which formerly contributed to the average flows for the "trunk" road types now contributed to the "non-trunk" averages, and vice versa, and so the averages changed. These changes in road lengths and in average flows introduced further discontinuities.
4.3.2 The apparent fall in the estimate of the total traffic volume for major roads between 1995 and 1996 is assumed to be due to the discontinuities caused by the above factors: in effect, the figures for 1995 and 1996 are on different bases, and are not directly comparable.
4.4 Method used to estimate traffic on major roads for 1993 to 1995 inclusive
4.4.1 The estimates for these years were produced by applying a very similar method, the only difference being that the calculations were performed for the areas of the nine former Regions and three Island Areas, rather than for the present Councils.
4.5 Method used to estimate traffic on major roads for 1992 and earlier years
4.5.1 Estimates for 1992 and earlier years were produced by the then Department of Transport (DOT) alone. Because the SO NRD automatic counters had not then been introduced, the scaling factors used in the DOT’s traffic estimates for Scotland for years prior to 1993 were calculated from manual "core" traffic counts at about 129 fixed sites throughout GB. (Although about 20 were in Scotland, it was the core counts for the whole of GB that were used.) These manual "core" counts were taken on three days each month of the year (a weekday, a Saturday and a Sunday) for 16 hours each day.
4.5.2 This change of method has implications for the traffic estimates for 1993 and later years, up to and including 1998, because the starting point for the estimates for 1993 was the traffic estimates for the individual road links which DOT had already derived for the year 1992 using the previous methods and, in particular, using GB "expansion" and "growth" factors derived from the GB manual "core" counts.
4.5.3 As a result, when the 1993 estimates were prepared, one-sixth of the major road links had traffic counts in 1993, and so required no growth factoring, leaving five-sixths of the links to have their 1992 traffic estimates (which had been derived by DOT) scaled forward by the "growth" factors for Scotland from the new NRD automatic "core" counters.
4.5.4 The earliest year for which there are estimates of the total volume of traffic on major roads in Scotland is 1983.
4.6 Method used to estimate traffic on minor roads for 1999 onwards
4.61 Estimates of traffic volumes on minor roads (B roads, C roads and unclassified roads) in Scotland by road type and vehicle type were produced by DTLR in conjunction with the SE RNMMD.
4.62 The method of estimation has two main stages. First, "12 hours on one day" traffic counts are taken at a "panel" sample of slightly over 200 sites on minor roads across Scotland. Taking the counts at the same sites each year should produce a better estimate of the year to year percentage change in the volume of traffic on minor roads. The sample was picked by the then DETR from a list of all the sites at which traffic counts had been taken between 1992 and 1997 (as described in a later section). Disproportionate stratified sampling, with a higher sampling fraction for roads which have a greater volume of traffic, was used, as this should produce more accurate results than a simple random sample of minor road sites. Sites with average flows of less than 200 vehicles per day were excluded altogether. As with the major road traffic counts, the minor road "12 hour" traffic counts must be "expanded" to estimate the flows for a whole day, and a whole year. This is done using expansion factors calculated from information recorded by a set of "core" automatic traffic classifiers located on a sample of minor roads across GB (there are not enough of them in Scotland to support the calculation of separate Scottish factors).
4.63 The estimates of minor road traffic volumes for the latest year are then calculated from the estimates for the previous year, using the estimated overall percentage change in traffic levels from the previous year (obtained from the results of the panel survey) and information about changes in the length of the road network between the two years.
4.7 Method used to estimate traffic on minor roads for 1998
4.71 The estimates of minor road traffic volumes for 1998 were calculated from the full set of traffic count data for the years 1992 to 1997, not from the 1998 panel sample results. The data for the sites counted in 1992 to 1997 were used because they provided a much larger and much more evenly-spread sample of minor roads than the panel sample in 1998 . The relevant growth and expansion factors from the GB-wide "core" automatic traffic classifiers were applied to each of the traffic counts taken in 1992 to 1997 in order to estimate the level of traffic at each site in 1998. The average traffic flows for each type of road were then combined with information about the lengths of roads of each type in Scotland as a whole, to estimate the total traffic volume (in millions of vehicle kilometres) in 1998 for minor roads, by road type and vehicle type, for Scotland as a whole.
4.8 Method used to estimate traffic on minor roads for 1997 and earlier years
4.8.1 In 1997 and earlier years, the sample of sites for the minor road traffic counts was chosen in a different way. Each year, a fresh sample of sites was picked by, in effect, taking a series of random points on a map, looking within a circle with a specified radius around each point, and identifying which (if any) minor road was nearest to the selected point. The number of other minor roads within the circle was used, at a later stage, when the results were grossed-up to produce the overall traffic estimates. This method of sampling was suitable for the production of results for GB as a whole, but not for Scotland: the kinds of minor roads in the Scottish sample could vary greatly from one year to the next, and, as a result, the Scottish component of the GB estimates was not sufficiently reliable to be published in its own right.
4.8.2 Over the years, the then DETR built up a list of all the minor road sites that had been chosen in this way, and this list, augmented with information about each site (such as the volume of traffic recorded in the count) became the basis for selecting the panel sample of minor road sites to be counted in 1998 and later years.
4.9 The information on pollutants is taken from the Scottish Executive National Statistics publication "Key Scottish Environment Statistics".
5. Further Information
5.1 Further information on GB road traffic statistics can be found in the annual DTLR publications "Road Traffic Statistics Great Britain" and "Transport Statistics Great Britain", and also in the former DETR's "Focus on Roads" and "Road Traffic Statistics Report" publications.
5.2 For enquiries about DTLR's methods of estimating road traffic, contact Mr Kerrick Macafee of the Department for Transport, Local Government and the Regions (Tel: 020 7944 6396).
5.3 For further information on average daily traffic flows at selected Automated Traffic Classifier (ATC) Sites and on key routes on the road network contact Mr Stuart Hay of The Scottish Executive Road Network Management and Maintenance Division (Tel: 0131 244 0458).
5.4 For further information on pollutants see "Key Scottish Environment Statistics", alternatively contact Dr Esther Roughsedge of The Scottish Executive, Environment Statistics branch (Tel: 0131 244 0439).
5.5 For further information on petrol and diesel deliveries contact Mr Ian Corrie of The Department of Trade and Industry, Energy Policy and Analysis Unit (Tel: 020 7215 2714).
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