The Scottish Abstract of Statistics No 26,1998

11 transport

Further information on the Notes, Definitions and Sources for all of the following sections can be found in "Scottish Transport Statistics" (available from The Stationery Bookshop).

Road Vehicles Licensing and Registration

11.1 Up to 1992, new registrations and total vehicles licensed were obtained from the Driver and Vehicle Licensing Agency (DVLA) Annual Vehicle Census. The statistics were a by-product of the administration of vehicle licensing, and the groups shown in the tables correspond in the main to taxation groups. The figures include all vehicles which pay tax and certain vehicles which are exempt.

11.2 In 1992, the source of this information changed to the Vehicle Information Database held by the Department of the Environment, Transport and the Regions (DETR). Minor technical changes in the methods used to determine if vehicles were properly licensed on "census day" were introduced with the change of source. Under the new system, more careful examination is made of vehicles that had complicated licensing histories, for example late payment, cheques that failed to clear, changes in taxation class, refunds or incorrect levels of duty paid. In addition, there was a change involving vehicles where the keeper was unknown or not properly registered. Previously such vehicles were allocated to regions of Great Britain on the basis of the previous keeper. The new system created a separate category for "address of current keeper unknown". These vehicles are included in the United Kingdom totals published by DETR and by the Office for National Statistics, but there is no allocation for such vehicles in the statistics for Scotland.

11.3 The result of these two changes is a small decrease in the estimated stock of licensed vehicles. The difference between the two sources can be broadly estimated from statistics for 1992, which are available from both the old and new sources. This indicates a 2.5% decrease for Scotland in the total number of vehicles licensed. To estimate the growth in licensed vehicles over the longer term these changes should be used to adjust the statistics to estimates vehicle growths. These changes do not affect the numbers of new registration of vehicles.

Bus and Coach Travel

11.4 The figures for table 11A3 are supplied by the bus and coach statistics branch of DETR. Further information is contained in the annual Scottish Office ‘Bus and Coach Statistics’ statistical bulletins, and DETR publications on this topic (available from The Stationery Bookshop).

11.5 The information has been derived from annual returns completed by a sample of Public Service Vehicle operators.

11.6 A local bus service is one available to the general public, where passengers pay seperate fares and travel a radial distance no greater than 15 miles (24 kilometres). Other services comprise contract, private hire, express journeys, excursions and tours which are not registered as local services.

Road Network

11.7 Information on road lengths is obtained by annual returns from the Council’s highway authorities.

11.8 The physical condition of Motorways and trunk roads is monitored by annual condition surveys which are undertaken for the Scottish Office 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). 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.

Road Traffic

11.9 Estimates of traffic volumes on major roads in Scotland by road type, vehicle type, and area within Scotland were produced by DETR in conjunction with The Scottish Office’s National Roads Directorate (SO NRD).

11.10 The method of estimation has two main stages. First, the SO NRD estimates traffic flows for approximately 1,800 individual road "links" on trunk and principal roads in Scotland. (A link is a section of road between two major intersections). Then, DETR summarises and weights the estimates of the traffic flows on these road "links" by 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 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 the Secretary of State is 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.

11.11 The SO NRD’s estimates of traffic flows for the individual major road "links" for each year were derived by a methodology, comparable to that used by DETR for the rest of GB, which involved 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, once every six years, on a rotating basis at each of the approximately 1,800 road links covering nearly all of the major road network in Scotland.

ii. The "core" counters which were used were the SO NRD’s automatic traffic counters at statistically random selected sites on major roads through Scotland. (For example, for the 1995 estimates, 54 "core" counters were used: 9 on Motorways, 26 on trunk A roads and 19 on local authority A roads). These automatic "core" counters classify the counts by category of vehicle according to their length and number of axles. The counters operate, on the whole, continuously: 24 hours per day, throughout the year.

11.12 The estimated traffic flows for each major road "link" for the "current" year were then derived from a series of calculations of which the following provides only a broad outline. The "core" traffic counters were used to derive two sets of scaling factors, which were then applied to each of the 1,800 "link" counts:-

a. "Whole year" factors for road type and vehicle type were derived from the "core" counters, 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 were also derived from the "core" counters, to scale estimated traffic flows in the previous year forward to the current year, for those links which were not counted in the current year.

11.13 DETR then produces the major road traffic volume estimates for Scotland from these individual "link" traffic flow estimates, and from information about the lengths of roads of various types in different areas. The calculations described below are performed for each road type, for each area.

i Average traffic flows for each road type and area for the "current" year are obtained by weighting the estimated traffic flows for the individual road links of that road type in that area by the lengths of those links.

ii. Estimates of the total traffic volume (vehicle kilometres) for each type of road in an area are then derived by multiplying the estimated average traffic flow for the road type and area by the total length of roads of that type in that area (from the road lengths returns: the lengths of Motorway slip roads are excluded from the calculations).

11.14 These calculations produce estimates of traffic volumes for each area. Estimates of traffic volumes for Scotland as a whole are then produced by adding up the estimates for the appropriate areas.

11.15 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 reorganisation of local government, and the changes which 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, because Regions/Islands were replaced by Councils. This introduced a discontinuity. The method of estimation (described above) multiplies the average traffic flows 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.

As a result, the figures for 1995 and 1996 are on different bases, and are not directly comparable.

11.16 Further details on the traffic estimates are provided in "Scottish Transport Statistics" and in the DETR publication "Road Traffic Statistics Great Britain".

Toll Bridges

11.17 There are four toll bridges in Scotland. The Forth Road Bridge was opened to traffic on 4 September 1964. The Tay Bridge was opened to traffic on 18 August, 1966, the Erskine Bridge on 2 July 1971 and the Skye Bridge on 16 October 1995.

11.18 Both the Forth and Tay bridges are run by Joint Boards whose members are drawn from the Edinburgh City and Fife Councils, and the Fife and Dundee City Councils, respectively. The two boards have full responsibility for the running of the bridges. The Erskine Bridge is a trunk road bridge and is the responsibility of the Secretary of State for Scotland. The Skye Bridge is run by Skye Bridge Ltd.

11.19 From 1 June 1991, one-way tolls were introduced for Tay Bridge southbound crossings. Northbound vehicles are no longer counted. From 1 September 1997, one-way tolls were introduced for Forth Road Bridge northbound crossings. Southbound vehicles are no longer counted. Therefore, the figure in table 11C1 represents one year’s northbound crossings plus only eight months’ southbound crossings. Using more detailed (unpublished) information, adding the figure for the first eight months of the year to that of the last four (doubled) gives an estimated total of around 21 million vehicles crossing the bridge in 1997.

Average Weekly Household Expenditure

11.20 The data in table 11C2 has been produced from the Office for National Statistics’ Family Expenditure Survey.

Injury Road Accidents

11.21 The statistics on injury road accidents are compiled from reports submitted by the police. The reports relate to accidents which occur on the public highway, involve a vehicle, result in death or personal injury and become known to the police. The Government has set a national target of a one-third reduction in total road casualties from the 1981-85 average level by the year 2000.

11.22 For more detailed statistics of injury road accidents and a full description of the terms used see "Road Accidents Scotland" (available from The Stationery Bookshop, price £8) and also the "Key Road Accident Statistics" Statistical Bulletin (available from The Stationery Bookshop, price £2).

Freight

11.23 This section deals with freight lifted and moved by road. The national statistics are derived from DETR’s Continuing Survey of Road Goods Transport which collects journey details of a sample of goods vehicles. The international statistics are derived from the International Road Haulage Survey.

11.24 Coastal shipping in table 11E1 covers Scottish coastwise shipping plus UK coastwise shipping with destination Scotland, less double counting of freight at origin and destination ports. Coastal shipping excludes foreign and one port freight shipping. The coverage of coastal shipping is different from the water transport port statistics provided in tables 11Gl to 11G6 where domestic water transport covers coastwise and one port freight shipping, but does not exclude double counting of freight at origin and destination ports.

Rail Services

11.25 Table 11F1 relates to passenger and freight traffic originating in Scotland on ScotRail, InterCity and Freight Services and based on DETR figures, in which actual returns are scaled so that all GB regions’ freight figures sum to a separately calculated GB total. The parcels forwarded information is compiled from data received from Red Star Parcels. The total numbers of passenger journeys originating in Scotland in 1993-94 and subsequent years have been estimated by The Scottish Office using information supplied by ScotRail and an allowance for the passenger numbers for other operators. The tonnages lifted in 1995-96 and 1996-97 have been estimated by The Scottish Office using information about the increases in the numbers of tonne-kilometres in those years.

Air Transport

11.26 Tables 11F3 to 11F7 are compiled from information supplied by the Civil Aviation Authority (CAA) by airport authorities and by UK airlines. Further information on UK civil aviation is available in the CAA’s regular publications.

11.27 An aircraft movement is an aircraft take-off or landing at an airport: one arrival and one departure are counted as two movements. Air transport movements are landings or take-offs of aircraft engaged in the transport of passengers or cargo on commercial terms. All scheduled service movements, whether loaded, empty or positioning; and charter movements transporting passengers or cargo and air taxi movements are included. A terminal passenger is a passenger joining or leaving an aircraft at the reporting airport. A passenger travelling between 2 reporting airports is counted twice, once at each airport. A transit passenger is one who arrives at and departs from a reporting airport on the some aircraft which is transiting the airport. Each transit passenger is counted once only. Cargo is the weight of property carried on an aircraft including, for example, the weight of vehicles, excess baggage, and diplomatic bags, but excluding mail and passengers’ and crews’ permitted luggage. Cargo in transit through the airport on the same aircraft is excluded. International services are services flown between the United Kingdom, Isle of Man and the Channel Islands, and places outside.

Water Transport

11.28 Most of the data are supplied by DETR. The Transport Division of The Scottish Office Development Department compile shipping service information from Caledonian MacBrayne and P&O Orkney and Shetland Services. Data are also supplied by the Orkney Islands Shipping Company. The figures for grants for harbour facilities (table 11G2) are from The Scottish Office Transport Division 2.

11.29 Coastwise traffic is traffic between ports of the United Kingdom. Foreign traffic is traffic between ports in the United Kingdom and other countries. One port traffic comprises dredged sand, gravel etc. traffic with offshore installations and materials shipped for dumping at sea. Domestic traffic is coastwise plus one port traffic. Container and roll-on traffic is commonly known as ‘unitised traffic’, including containers carried on all types of shipping services, plus road goods vehicles, other goods carried on roll-on/roll-off, shipping services and rail wagons and barges carried on ships. Inland waterways are waterways bounded by the furthest point downstream which is less than both 3 km wide at low tide and 5 km wide at high tide (spring). See also note 11.7.

Personal and Cross-Modal Travel

11.30 Information about travel (within Great Britain) by Scottish residents is obtained from the National Travel Survey (NTS). This collects "travel diary" details from a sample of households across Great Britain. Travel for all private purposes is included. Journeys in the course of work are included if they fulfill the requirement that the main reason for the journey is for the traveller to reach the destination. However, travel in the course of work to convey passengers or to deliver goods is excluded, such as travel in the course of their work by bus drivers, lorry drivers and postmen. Journeys off the public highway, such as country walks, are excluded.

11.31 The NTS is not designed to provide reliable estimates for Scotland for single years: the sample includes only a few hundred Scottish households each year. Therefore, the samples for a number of years must be combined in order to produce Scottish results, and even they will be subject to sampling variability.