Domestic road freight statistics: Methodology note
Published 24 January 2023
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This publication is available at https://www.gov.uk/government/statistics/domestic-road-freight-statistics-july-2021-to-june-2022/domestic-road-freight-statistics-methodology-note
Overview
This note provides an overview of the changes made to the Continuing Survey of Road Goods Transport (CSRGT) that is used by the Department for Transport (DfT) to collect domestic road freight statistics. This methodology note is intended to inform users of the changes, including improvements and impacts to the data.
The Continuing Survey of Road Goods Transport Great Britain (CSRGT GB) and Northern Ireland (CSRGT NI) measure the UK activity of GB and NI registered heavy goods vehicles (HGVs) operating in the UK respectively. The survey moved from paper forms to online questionnaires partway through 2021.
Important note for users
Following a detailed investigation into the CSRGT data to determine the effects of the methodology change from paper to online data collection, it has been concluded that data from the paper surveys pre July to September 2021 (quarter 3) and data from online surveys, July to September 2021 (quarter 3) onwards, should not be compared.
CSRGT uses a stratified sample of HGVs to collect data for one week of road freight activity from the vehicle operator, with the sample of vehicles selected from vehicle records maintained by the Driver and Vehicle Licensing Agency (DVLA). More information on the CSRGT sampling method is available .
The sections below outline the methodology change in more detail, including the overall improvements following the methodology change and impacts to the data.
Details of change to methodology
In keeping with DfT’s strategy of producing and maintaining high quality statistics, the Road Freight Statistics Team have improved the process to collect domestic road freight statistics.
Previously, data collected from CSRGT was via paper questionnaires. While those selected to complete the survey forms are required to do so under the Statistics of Trade Act 1947, identifying non-respondents was a time intensive process.
Midway through 2021, the survey forms transitioned from paper to online format. Here, the vehicle operator provides the same information as previously requested under the paper survey format.
The online survey has been made more intuitive compared with the paper survey based on extensive user testing. The structure has been streamlined and guidance provided for each relevant question to aid interpretation. This increases the likelihood of respondents providing information that more accurately reflects the vehicles true activity, therefore providing more accurate estimates of the overall HGV population.
In addition, it has now become simpler to increase data validation checks to ensure survey responses are accurate, which has improved the overall accuracy of the data.
Impacts of methodology change
In accordance with Office for Statistics Regulation (OSR) guidance on changes to statistical methods, CSRGTs revised data collection process has been assessed against The Code of Practice for Statistics to clearly communicate findings to all users of the Domestic Road Freight statistics.
As with all sample survey data, information collected are estimates of the unknown population values and therefore should be treated with a degree of caution. Data from paper surveys within the Domestic Road Freight Statistics represented the best estimates of the HGV population at the time of surveying.
Online road freight data now collected as part of an improved methodology and following an increased response rate, represents an improved estimate of the activity of the HGV population. An investigation into data from the new surveys determined that whilst there was no clear change in the trend of distance travelled by HGVs, there was an observable increase in the weight of goods lifted by HGVs at the point of the survey moving from paper to online.
Having reviewed the possible explanations for this change, it has been determined that comparability of the data has been impacted and as a result, comparisons between paper and online data within the Domestic Road Freight publication should not be made. This has been determined based on the following observed changes since CSRGT moved to online data collection:
- Increased weight of goods lifted
- Increase in proportion of heavier HGV journeys
- Increase in overall response rate
- Additional external factors (EU Exit, COVID-19)
The methodology change occurred during a period of significant volatility in the road freight sector following the UK’s exit from the European Union, the COVID-19 pandemic and recruitment and retention challenges for HGV drivers. This background of changing patterns of road freight means is it not possible to identify or account for the data changes caused solely by the methodology change.
When referring to the Domestic Road Freight publication, users will be notified of the methodology change within relevant charts and tables. Users will be reminded that caution should be taken when looking at trends over time and making comparisons before and after the methodology change.
Summary of Investigation
Details of each component of the methodology investigation can be found below.
Weight of goods lifted for journeys with many stops
Following the survey moving online, the gross weight of goods lifted by HGVs within the UK increased above pre-pandemic levels, with a noticeable increase in the proportion of total weight of goods lifted by HGVs completing many-stop journeys. These journeys are defined as HGVs making 6 stops or more and are typically carried out by larger rigid and articulated HGVs being used to both deliver and/or collect goods at each stop within a journey. This is supported by the significant increase in total and average weight of goods lifted by the heaviest rigid HGV weight category (over 26 tonnes) and heaviest articulated HGV weight category (over 40 tonnes) conducting many-stop journeys.
In contrast, data trends of few stop journeys (journeys with fewer than 6 stops) appeared largely unchanged following the move to online.
In the CSRGT, HGV operators making journeys with many stops are only asked to report summary information rather than record their entire journey. Before moving online, respondents were sent a paper form with separate sections based on the type of journey completed (fewer than 6 stops, or 6 stops or more). Respondents would be required to read all sections of the survey to ensure they completed the correct section, with guidance provided in a separate paper document. For the online version, respondents are asked a series of questions, whereby their responses direct them to the relevant sections.
Analysis of survey responses suggested that the more-intuitive structure of the new online form may have meant some respondents provided more complete answers for many-stop journeys. This was based on a statistically significant fall in the number of respondents reporting journeys with 5 stops after the introduction of the online form, with 5 stops versus 6 stops the cut-off between a ‘few-stop’ and ‘many-stop’ journey. However, the evidence was not fully conclusive, and as shown in chart 3 below, the weight of goods carried on many-stop journeys had also been increasing prior to the methodology change. This conflation of trends means that it is not possible to isolate the impact of the new methodology.
Chart 1: Average ungrossed weight of goods lifted per stop (tonnes) by HGVs completing journeys with few stops (fewer than 6) – January to March 2016 (quarter 1) to April to June 2022 (quarter 2)
Chart 2: Average ungrossed weight of goods lifted per stop (tonnes) by HGVs completing journeys with many stops (6 or more) – January to March 2016 (quarter 1) to April to June 2022 (quarter 2)
Heavier many-stop HGV journeys
Following the observed increase in proportion of total goods lifted by HGVs completing journeys with many stops, further observations were made regarding the weight of completed journeys.
Between January to March 2016 (quarter 1) and April to June 2021 (quarter 2), 9% of HGV journeys with 6 stops or more carried over 100 tonnes, on average each quarter. Between July to September 2021 (quarter 3) and April to June 2022 (quarter 2), this increased to 18%.
This indicates that since the survey transitioned from paper to online, more HGVs are reporting heavier journeys. This finding has been identified as one of the primary drivers of increased weight of goods lifted. Similar to the previous finding, whilst there was a sizable increase coinciding with the methodology change, the proportion of heavier many-stop journeys had also been increasing prior to the methodology change. Again, this conflation of trends means it is not possible to isolate the impact of the methodology change.
Chart 3: Percentage of many-stop journeys over 100 tonnes – January to March 2016 (quarter 1) to April to June 2022 (quarter 2)
Survey response rate
With the survey now online and the Road Freight Statistics team able to identify respondents who have yet to complete the survey, the overall response rate has increased as a result. The response rate is the number of HGVs selected for sampling whose operators provide completed survey returns, divided by the total number of HGVs selected for sampling.
When the survey was in paper format, the average response rate between January to March 2019 (quarter 1) and April to June 2021 (quarter 2) was 76%. With the survey now online and the improvements made to traceability of incomplete surveys, the average response rate between July to September 2021 (quarter 3) and April to June 2022 (quarter 2) has risen to 95% (see table 1 below). The statistics produced from these surveys are calculated using grossing factors which account for the response rate in each quarter. Due to potential bias in non-responses, however, this increase has likely resulted in the data becoming more accurate and more representative of the HGV population at the time of sampling.
Table 1. CSRGT response rate, January to March 2019 (quarter 1) to April to June 2022 (quarter 2)
| Quarter | HGVs Selected | Responded* |
|---|---|---|
| Jan to Mar 2019 (quarter 1) | 3,404 | 2,922 (86%) |
| Apr to Jun 2019 (quarter 2) | 3,406 | 2,823 (83%) |
| Jul to Sep 2019 (quarter 3) | 3,389 | 2,868 (85%) |
| Oct to Dec 2019 (quarter 4) | 3,384 | 2,757 (81%) |
| Jan to Mar 2020 (quarter 1) | 3,391 | 2,658 (78%) |
| Apr to Jun 2020 (quarter 2) | 3,441 | 2,460 (71%) |
| Jul to Sep 2020 (quarter 3) | 3,443 | 2,438 (73%) |
| Oct to Dec 2020 (quarter 4) | 3,418 | 2,391 (70%) |
| Jan to Mar 2021 (quarter 1) | 3,776 | 2,497 (66%) |
| Apr to Jun 2021 (quarter 2) | 3,266 | 2,272 (70%) |
| Jul to Sep 2021 (quarter 3)** | 3,430 | 2,866 (84%) |
| Oct to Dec 2021 (quarter 4) | 3,197 | 3,126 (98%) |
| Jan to Mar 2022 (quarter 1) | 3,216 | 3,157 (98%) |
| Apr to Jun 2022 (quarter 2) | 3,261 | 3,252 (99.7%) |
Note:
*Percentages are rounded
** Survey moved online
New respondents
To understand whether any new respondents were influencing the data, businesses who had not responded within a 5-year period from the July to September 2021 (quarter 3) data returns were isolated and examined separately. The outcome of this investigation found that new businesses accounted for no more than 1% difference in the grossed weight of goods lifted.
Proportion of survey respondents reporting road freight activity
Examining the percentage of survey respondents who reported road freight activity during their survey period, there has been an observable increase in the reported rate of road freight activity in line with the increased response rate.
Chart 4: Percentage of survey responses reporting road freight activity compared to the total proportion of responses
Chart 4 above shows that between January to March 2019 (quarter 1) and April to June 2022 (quarter 2), the proportion of respondents reporting road freight activity has largely changed proportionally with response rate. This suggests that there has been no observable change in the proportion of HGVs undertaking road freight activity following the survey moving online, but rather the rate of HGVs undertaking activity has remained dependent on response rate.
Additional factors
While there have been observable changes to the data following the survey transitioning from paper to online, as outlined above, there are additional factors that may have impacted the data that are not possible to capture independently.
COVID-19, economic impacts, and recruitment challenges for HGV drivers
Given the impact the COVID-19 pandemic had on the national and global economy, it is possible that the operations of HGVs and haulage companies have altered to reflect ongoing inflation, particularly with rising fuel prices. Additionally, DfT has been acting to respond to reported shortages of HGV drivers. More information on the government’s response is available.
The evidence shown above about increasing the average weight of goods carried per journey may suggest efforts by haulage companies to increase efficiencies and adopt more cost-effective strategies.
While changes to average journey weights have been observed in the new online data, it is not possible to confidently assume these are down to operational changes alone.
EU Exit
The UK’s withdrawal from the European Union is likely to have had an impact on practices within the UK road freight industry, with changes to vehicle operating license requirements, customs, and regulation changes all resulting in a possible change to the business activity of UK haulage companies.
Trends from DfT’s international road freight statistics indicate a decrease in goods lifted to and from the UK by UK-registered HGVs since April to June 2019 (quarter 2). Whilst this trend will not individually explain the change in data within the domestic road freight statistics, it could be a contributing factor if more haulage companies are conducting less international work and replacing this with increased domestic activity.
Next steps
Alongside the standard data quality checks implemented for any statistical publication, the road freight statistics team will continue to monitor CSRGT quarterly online survey data for any significant changes in trends of both weight of goods lifted and distance travelled by HGVs that cannot be explained by external factors.