Background Notes

Survey Methodology

Introduction

This report contains the results of the "National Survey of Transport of Goods by Road" which is conducted on a weekly basis throughout the year.

Legal framework

This is a statutory survey conducted under the Statistics (Road Freight) Order, 2016 (SI No 146 of 2016) to meet Ireland’s EU requirements under Council Regulation (EC) 70/2012 on statistical returns in respect of the carriage of goods by road.

Scope of the survey

This report covers the survey period beginning the first week of January 2017 and ending the last week of December 2017. Irish registered vehicles that come within the scope of the survey must meet the following criteria:

1. belong to the motor taxation class ‘Goods Vehicles’
2. have a valid motor tax disk during the relevant survey week. However, in practice, as the survey sample was selected several weeks before the survey week, vehicles where the motor tax had expired no more than three months previously were also included in the scope.
3. have an unladen weight of two tonnes and over
4. have a vehicular body type appropriate for carrying freight (see appendix B for a list of vehicular types that have been excluded).

No other vehicles are covered. In particular this means that vehicles in other motor taxation classes such as agricultural tractors, general haulage tractors, dumpers and exempt vehicles (i.e. vehicles exempt from liability to pay road tax which includes state owned, diplomatic, fire services or disabled drivers) are not included in the survey.

All activity of goods vehicles within the scope of the survey engaged in the carriage of goods on the public road, either on own account or for hire or reward, are covered.  Excluded, therefore, is activity such as site work off the public road or work of a mainly service nature (e.g. carriage of personnel to or from places of work). 

Sampling frame

The sampling frame for the Survey comes from the Department of Transport, Tourism and Sport’s database on vehicles taxed as goods vehicles.

The sampling frame/register is updated every eight weeks during the year with information from the Department regarding vehicles:

1. being registered for the first time
2. having their motor taxation class changed
3. being formally scrapped
4. having their registered owner changed. 

The information required of each vehicle on the register for survey purposes is as follows:

a)    year of manufacture of the vehicle
b)    date of first registration of the vehicle
c)    an indication as to whether the vehicle has been taxed for the carriage of goods on own account or for hire or reward
d)    the unladen weight of the vehicle
e)    name and address of the person on whose name the vehicle was most recently taxed (referred to as the owner of the vehicle in the following paragraphs).

Periodicity

The results are published on an annual basis.

Sample design

Information is collected in respect of one week’s transport activity for a random sample of goods vehicles.   Every week a sample of vehicles is selected from the register. A survey questionnaire is then issued to the registered owners of these vehicles by post, seeking information on the vehicle and an account of the vehicle’s activity during that week. For the purposes of sample selection, vehicles are divided into 20 strata.  These strata were created on the basis of four criteria:

• the unladen weight of the vehicle
• year of first registration of the vehicle
• whether the vehicle had been taxed for the carriage of goods on own account or for hire or reward
• year of manufacture.

See Table L

Response rates

Out of a total of 23,351 vehicles surveyed, a satisfactory return was received in respect of 11,417 vehicles, representing an overall response rate of 49%.  However, this rate varied across the differing survey strata.  Response rates broken down by the unladen weight and the year of manufacture of vehicle are presented in Table M.

See Table M

Changes to commodity classification

In 2007, the standard goods classification for transport statistics, NST/R, was revised by the United Nations Economic Commission for Europe (UNECE).  A new version, NST 2007, was introduced to be consistent with the revised NACE (Statistical Classification of Economic Activities in the European Community).  This new goods classification came into force in 2008.

Accordingly, the goods commodities collected in the “National Survey of Transport of Goods by Road” have been revised in line with this new goods classification, effective from 2009 onwards. Unfortunately, this revision means that the results by commodity in this publication for 2017 are not directly comparable with 2008 or previous years.

Reliability of results

Estimation of survey results from data relating to only one week’s activity for a sample of vehicles introduces a statistical variability which would not be present if a full year’s data had been collected for every vehicle. This means that the survey results cannot be taken as accurate to the full degree shown in this report.

This variability is expressed by means of the coefficient of variation. This coefficient gives the relative size of the “sampling error” (variability) present in an estimate compared with the estimate itself. In general, estimates can be said to have a relative precision of twice their coefficient of variation. The estimated coefficients of variation for the overall tonnes carried, tonne-kilometres and vehicle kilometres estimates are shown in Table N below.

In general, the more detailed the classification provided the greater the coefficient of variation of the estimates.  In the derivation of the results the assumption is made that non-respondents have similar characteristics and activity levels to those of respondents in the same stratification cell.  This assumption, which is a standard one in surveys such as this, may result in some degree of bias being introduced into the results. Moreover, although every effort is made to ensure that the returns received are correct in all respects it is inevitable that some minor non-sampling errors remain undetected.

Rounding: Due to the fact that individual figures have been rounded independently there may be slight discrepancies between the sum of the constituent items and the totals shown.

See Table N

Definitions used

Type of journey

Two basic categories of journey are distinguished – split delivery/collection journeys and end-to-end journeys.

• End-to-end journeys are those which have no intermediate collection or delivery points between their origin and destination.
• Split delivery/collection journeys involve the depositing and/or collection of part of the load carried at one or more stopping points along the way. A common example of such a journey would be the delivery of beer to public houses and the collection of empties.

Tonnes carried

• This is the weight of goods (including empties) carried inclusive of packaging etc. but excluding the weight of demountable containers (if any) in which the goods are carried.
• For split delivery/collection journeys tonnes carried are taken as the weight of goods at the start of the journey plus the weight of any other goods collected during the journey.

Tonne-kilometres (tonne-km)

• For end-to-end journeys this is the result of multiplying the weight of goods carried by the distance they were carried.
• For split delivery/collection journeys more complex formulae were used.  These involved multiplying the distance travelled with a load by an estimate of the average weight of load carried.

National transport

National transport is the carriage of goods by road by Irish registered goods vehicles between two places (a place of loading/embarkment and a place of unloading/disembarkment) both of which are located in the Republic of Ireland.

Appendix A

NUTS2 and NUTS3 regions

The regional classifications in this release are based on the NUTS (Nomenclature of Territorial Units) classification used by Eurostat.  The NUTS3 regions correspond to the eight Regional Authorities established under the Local Government Act, 1991 (Regional Authorities) (Establishment) Order, 1993, which came into operation on 1 January 1994. The NUTS2 regions, which were proposed by Government and agreed by Eurostat in 1999, are groupings of the NUTS3 regions. The composition of the regions is set out below.

Border: Cavan, Donegal, Leitrim, Louth, Monaghan and Sligo.
Midland: Laois, Longford, Offaly, and Westmeath.
West: Galway City and County, Mayo and Roscommon.
Dublin: Dublin City, Dun Laoghaire-Rathdown, Fingal, and South Dublin.
Mid-East: Kildare, Meath and Wicklow.
Mid-West: Limerick City and County, Clare and North Tipperary.
South-East: Waterford City and County, Carlow, Kilkenny, South Tipperary and Wexford.
South-West: Cork City and County and County of Kerry. 

See Appendix B below.

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