Demographic and Infrastructure: Data Definitions and Caveats

There are many sources of data on national populations, and they often disagree in detail. This is partly because of questions over who should be included, and partly because of the need to correct for factors such as non-returns in censuses and illegal immigrants. Overall, there is uncertainty of at least 0.5 per cent in any quoted figure. Forecasts of population depend on many assumptions, and are more uncertain.

Even a well-defined quantity such as the surface area of a country is given different values by different sources, but the differences are generally small.

The Gross Domestic Product (GDP) provides a measure of the total economic activity in a country or region. There are various ways of estimating GDP, and the result can be expressed in units of local currency, or converted to $US at an official exchange rate, or expressed as $US 'Purchasing Power Parity' (PPP). That is, how many $US would be needed in USA to purchase the goods and services produced by the local economy.

For EU Member States, fuller information is available in EU Energy and Transport in Figures.

The road network is separated into motorways, national or state roads, regional or provincial roads and local roads. Because the organisation of government varies between countries, the terms national, state, regional and provincial mean different things in different countries.

'Motorway' is generally a functional description, implying a dual carriageway road with grade separated junctions, from which certain classes of traffic are excluded (for example, pedestrians, pedal cyclists, animal transport and learner drivers). In some countries this is not the case.

The rail network is listed as the total and the high-speed network (high speed is listed by the International Union of Railways (UIC) as tracks on which trains operate at over 250km/h, at over 200km/h and at under 200km/h).

Details related to the land area (for example, whether it includes areas of water such as lakes and rivers, and where the seaward end of a river is defined to be) are not typically defined in the datasets that provide the values for this database. Different sources give values for the area of a country that often differ by 0.5 per cent. Particular uncertainties for individual countries are:

• Great Britain and UK: Does the area quoted include the Channel Islands and the Isle of Man, which are not part of the UK? There is additional potential confusion between Great Britain (England, Scotland and Wales) and the UK (Great Britain plus Northern Ireland).
• France: Does the area consist of only Metropolitan France or include overseas territories?
• Spain: Does the area include the Canary and Balearic Islands and the Spanish enclaves in North Africa?
• India: How much of Kashmir along the undefined 'Line of Control' is included?

This is usually defined as the length of the centre lines of the road system. Whether additional parts of the road network such as slip roads and service roads count as additional length or are included in the length of the major road they support is often uncertain. In general, private and industrial roads are excluded from national totals. An exception is Canada, which records the length of roads as the length of two-lane equivalent roads. Thus 1km of four-lane road is 2km of a two-lane equivalent road.

An occasional problem is the omission of certain classes of road from national totals. Thus Spain frequently excludes roads managed by metropolitan governments from national totals.

Different sources, and year-to-year variation of values, suggest that the national total road length may well not be known to be better than 10 per cent in some countries. Omissions of certain classes of road can lead to errors of the order of 50 per cent.

US National Transportation Statistics 2005 Appendix C include the following abridged statement on the accuracy of road length data: "The Federal Highway Administration (FHWA) of the U.S. Department of Transportation (USDOT) collects and reviews state-reported Highway Performance Monitoring System (HPMS) data for completeness, consistency, and adherence to specifications. Some inaccuracy may arise from variations across states in their adherence to federal guidelines.

Beginning with the 1997 issue of Highway Statistics, FHWA instituted a new method for creating mileage-based tables derived from the HPMS. Previously, adjustments to tables developed from sample data were made using area-wide mileage information provided by states. These adjustments are now being made using universe totals from the HPMS dataset. Users may note minor differences in table-to-table totals.

Reliability may be diminished for comparisons with pre-1980 data, which were collected via different methods and special national studies. For instance, pre-1980 mileage data included some nonpublic roadways (95,000 miles in 1979) while post-1980 data reports only public road mileage (roads or streets governed and maintained by a public authority and open to public travel)."

Motorways

Motorways are known in different countries by titles such as autobahn, autoroute, autostrada, interstate, expressway or freeway. Most countries define a motorway as a dual carriageway road with grade separated junctions from which certain classes of road-user, such as pedestrians and pedal cyclists, are excluded.

Issues arise over whether roads that have these characteristics, but are not designated motorways, should be included. For example, in USA in 2003, there were 74,845km of 'principal arterials, interstates'; 15,884km of 'principal arterials, expressways'; and 247,684km of 'principal arterials, other'. It is not clear what proportion of the principal arterials network are motorways. In the Transport Statistics database only interstates are counted as motorways for the length of motorways in USA.

National or State Roads

All the nations in the database have a limited network of strategic roads built and maintained by the national government: trunk roads in Britain (some of which are motorways); US roads in USA; Routes Nationales in France. IRF World Road Statistics lists the length of national roads, and national government figures can be used to determine the classes of road considered by IRF to be national roads.

One issue that is not always clear in national statistics is whether motorways are included in, or additional to, the national roads. Moreover, many countries are transferring some national roads to local government - in Britain this is termed 'de-trunking'. Because of this change in classification, the national road network may appear to reduce in length with no functional change on the ground.

China and India are also examples illustrating the difficulties raised by the categorisation system in different countries. China classifies roads as Class I to IV Highways; the China Statistical Yearbook definitions do not explain which are national, regional or local. India classifies Highways as Public Works Department roads, subdivided as National, State and other, and Panchayat (village elected council) roads in various categories. In addition, there are urban roads (including 'railway roads') and project roads.

Regional or Provincial Roads

Almost all countries have a network of strategic roads that are managed by local government. In USA they are State roads; in France they are Departmental roads; in Britain, the database has considered Principal roads (non-trunk A roads) as Regional roads.

Local Roads

Local roads are reasonably well defined in most countries, but data on the length of the local road network is often incomplete, estimated or approximate. They usually make up more than half the total road network.

Urban Roads/Highways

In Great Britain urban roads are major and minor roads within an urban area with a population of 10,000 or more. Roads are also classified as 'built-up', with a speed limit of 40 mph or less. In the USA urban roads are defined as any road or street within the boundaries of an urban area (an urban areas being an area including, and adjacent to, a municipality or urban place with a population of 5,000 or more).

Rural Roads/Highways

In Great Britain rural roads are any major or minor roads outside urban areas. In the USA, any highway, road, or street that is not an urban highway falls into this category.

The length of the rail network is available from government statistics and, for many countries, from UIC (International Union of Railways) . The length is usually that of routes, regardless of the number of tracks and typically ignores the length of tracks in sidings, yards, etc.

UIC and Eurostats provide data on the length of high speed rail lines. Eurostats gives a single figure for each country, but UIC has data on the lengths separately for routes operable at speeds of less than 200km/h, 200-249km/h and 250+km/h. however, this is not tabulated in the time series data for 1970 to 1999, only in annual data sets. the transport statistics database uses the length of routes for 250+km/h as the length of high speed lines.

In Great Britain, drivers are defined as persons in control of vehicles other than pedal cycles, two-wheel motor vehicles and ridden animals; passengers as other occupants of vehicles; pedal cyclists as riders of pedal cycles, including any passengers; riders as persons in control of pedal cycles, two-wheel motor vehicles or ridden animals (other occupants of these vehicles are passengers); and pedestrians as persons riding toy cycles on the footway, persons pushing bicycles, pushing or pulling other vehicles or operating pedestrian-controlled vehicles, those leading or herding animals, occupants of prams or wheelchairs, and people who alight from other vehicles and are subsequently injured.

In the USA, road-users are listed as:
• Passenger car occupants;
• Light-truck occupants (light trucks are trucks of 10,000 pounds or less gross vehicle weight, including pickups, vans, truck-based station wagons, and sport utility vehicles (SUVs));
• Pedestrians struck by motor vehicles (pedestrians defined as any person not in or on a motor vehicle or other vehicle);
• 'Other pedestrians' refers to pedestrians using conveyances and people in buildings (conveyances include skateboards, non-motorised wheelchairs, roller skates and sleds);
• Motorcycle: a two- or three-wheeled motor vehicle designed to transport one or two people, including motor scooters, minibikes and mopeds;
• Large-truck occupants (large trucks are trucks over 10,000 pounds gross vehicle weight, including single-unit trucks and truck tractors);
• Pedal cyclists struck by motor vehicles; Pedal cyclist is a person on a vehicle that is powered solely by pedals;
• Other nonoccupants struck by motor vehicles ( a nonoccupant being any person who is not an occupant of a motor vehicle in transport (e.g. bystanders, pedestrians, pedal cyclists or an occupant of a parked motor vehicle);
• Bus occupants (school, intercity and transit)
• Other and unknown motor vehicle occupants.

Fatalities not related to transit bus and demand responsive transit accidents are not included under highway sub-modes.

The IRTAD database lists fatal casualties as 'total', 'pedestrians', 'bicyclists', and 'occupants of passenger cars and station wagons'. 'Other road users' can be deduced by subtraction.

There are many sources of data on national populations, and they often disagree in detail. National government figures are used where available for the Transport Statistics database. Where these are not available, data from UN, OECD, World Bank and CIA are considered the most reliable. A useful additional source is the Populstat website which provides historical population data for very many countries. A cause of uncertainty is changes in national borders over time.

The way in which population figures are revised, and differences between sources, suggests that for many countries the total population is uncertain to perhaps 1% and possibly more. This uncertainty varies between countries; in developing countries it is probably larger.

These are available from many national government census organizations, from Eurostats, to 2030 from the UN World Urbanisation Prospects: 2007 revision and to 2050 from UN World Population Prospects: 2006 revision. They are also available from Populstat.