2. Methodology

Seatbelt and Mobile Phone Usage Survey Scotland, 2017

2. Methodology

2.1. Site selection

The surveys were carried out by a series of roadside observations at 30 sites in Scotland, including different road (major and minor[13]) and area (urban and rural[14]) types to provide nationally representative estimates. Sites were chosen in locations across Scotland to reflect different levels of road use and traffic volume, and included a number of sites which have been used in previous DfT seatbelt studies[15].

Observation of mobile phone use took place on roads with moving (free-flowing) and stationary (at traffic light controlled junctions) traffic, although the seatbelt survey was only undertaken at stationary sites.

A breakdown of the sites by road and area category is outlined in table 2.1. Further details about the survey sites, including location, are provided in Appendix C.

Table 2.1: Distribution of sites in Scotland by site characteristics
Scotland Stationary sites Moving sites Total
Rural Urban Rural Urban
Major 5 6 4 2 17
Minor 2 7 2 2 13
Total 7 13 6 4 30

2.2. Data collection

Roadside observations were made of occupants of cars, vans, taxis, private hire, lorries and buses, coaches, and mini-buses.

At moving sites, the gender of drivers was recorded by road side observers along with whether they were using a hand-held mobile phone, and if so, whether this was to make a call (at-ear) or some other function (in-hand), for example texting.

At stationary sites, the same information as above was recorded for the mobile phone element with driver age and the presence of passengers also recorded.

Additional information was collected on seatbelt use, age, gender and seating position of all vehicle occupants, except buses and coaches where only information on driver characteristics were recorded. The seatbelt details included additional age categories for children and whether the appropriate child restraint was being used correctly.

The information recorded is outlined in Table 2.2.

Table 2.2: Information recorded by survey and site type ( √ recorded, X = not recorded)
Seatbelt stationary sites Mobile phone stationary sites Mobile phone moving sites
Vehicle characteristics Type: car, van, taxi, private hire, lorry, bus (or minibus or coach)
Passengers present x x
Driver characteristics Gender
Age group x
Hand-held mobile phone use x
Purpose of hand-held mobile phone use x
Driver restraint use x x
Passenger characteristics Seating position x x
Gender x x
Age group x x
Restraint use x x

Surveys were conducted during half-hour observation periods in September and October 2017. An issue with the quality of the data collected at five Scottish moving sites (for mobile phone observations only) resulted in fieldwork being repeated at the affected sites in June 2018.

Each survey site was visited for a half-day session[16] during the week, with selected sites being revisited on Saturdays to provide a representative estimate of behaviour on weekdays and at weekends.

A breakdown of the session times is provided in table 2.3.

Table 2.3: Survey session times
Morning Session Afternoon Session
Start End Start End
07:30 08:00 13:30 14:00
08:30 09:00 14:30 15:00
09:30 10:00 15:30 16:00
10:30 11:00 16:30 17:00
11:30 12:00 17:30 18:00

Overall, the survey periods accounted for both the morning and evening peak periods so provide a reliable estimate of mobile phone use and seatbelt compliance throughout the day.

2.3. Weighting and analysis

During all survey periods, traffic counts of all vehicles passing the site were made. This included vehicles where no in-depth observation details were recorded, either because the observer could not accurately record information (if a vehicle passed too quickly or visibility was poor) or because the vehicle was not part of the sample (for example, a moving vehicle passing a stationary site during a green-light phase).

Following collection, the data were quality assured before being weighted using the recorded traffic count and DfT traffic flow data to provide a nationally representative estimate for Scotland across different road and area types.

Therefore, seatbelt wearing rates were calculated as the (weighted) number of relevant vehicle occupants correctly restrained over the (weighted) number of all relevant occupants observed[17]. In the same way, mobile phone usage rates were calculated as the (weighted) number of drivers using a hand-held mobile phone (at-ear and in-hand combined) over the (weighted) number of all drivers observed.

It is worth noting that some records were excluded from certain elements of the analysis process and this is reflected in the sample sizes detailed. The most notable exclusions were:

  • records where mobile phone or seatbelt use was recorded as unknown
  • records where vehicle type was recorded as unknown
  • records where gender or age were unknown and these were variables being analysed

The majority of the results presented in this report are based on data recorded during weekday observations. Analysis based on data collected at weekends is highlighted where appropriate.

For the purposes of analysis, car drivers and passengers in the survey results includes occupants of private cars, taxis, and private hire vehicles unless otherwise stated. The 'other vehicle' category includes drivers and passengers of vans, lorries, buses, coaches, and minibuses, unless otherwise stated.

When referring to passengers, the seatbelt usage rate also includes the correct use of child restraints where children have been observed in the vehicle.

Where charts are used to present results, the corresponding tables can be found in Appendices A and B. These tables provide details of the data behind the charts as well as an indication of the relevant sample sizes.

Figures relating to the wearing rates in England and across Great Britain have been provided by the Department for Transport and may be calculated in a different way from the figures for Scotland. Further information and comparisons are available in the DfT (2019) publication Seatbelt and Mobile Phone Use Surveys: Great Britain, 2017.

For the mobile phone survey, usage rates are presented separately for moving and stationary sites as it is possible that the prevalence and type of mobile phone use may vary across different driving situations. Moreover, the data recorded and the weightings applied during the analysis process differed between the site categories.

Statistical tests have not been carried out to determine whether differences between Scotland and Great Britain or between groups (e.g. male or female) are statistically significant.

2.4. Comparability

The results reported for seatbelt compliance in Scotland in 2017 are comparable with the DfT analysis of the 2017 England and Great Britain data as the findings were established using the same recording, weighting and analysis procedures. The methodology employed in the seatbelt survey is the same as previous studies so figures presented in this report are also comparable with historical data, for example data related to Scotland in 2014 and 2009. Specifically, it is worth noting is that the fieldwork for the 2014 and 2009 seatbelt surveys were also conducted in October, although some 2017 seatbelt sites were surveyed in September.

The comparability of mobile phone use at moving sites has been impaired by the resurveying of five sites in June 2018 following issues raised in relation to the quality of the data. This means that results relating to mobile phone use at moving sites in Scotland are not directly comparable with the DfT 2017 England and Great Britain data as these were collected in the autumn of 2017. The comparability of mobile phone use at stationary sites in Scotland remains unaffected as these surveys were carried out at the same time as the England and Wales surveys.

2.5. Limitations

The survey findings are generally limited by the reliance on the judgement of roadside observers (for instance, on gender and age). However, this risk was present in all previous examples of the study, yet reliable findings were still achieved due to the large volume of observations made and the weightings procedure followed during analysis. In addition, observers were given extensive training and the data were quality assured prior to analysis.

As previously noted, five of the moving sites were resurveyed in June 2018. This has meant that the results for mobile phone use at moving sites in Scotland are not comparable with the England and Great Britain results as these refer to data collected exclusively in the autumn of 2017.

It is possible that visibility could have been restricted by poor lighting, tinted windows or glare, particularly at moving sites. This may have led to inaccurate data being recorded or certain details being missed. The survey session times were scheduled to avoid problems of poor lighting as far as possible.

Roadside observers were wearing high-visibility jackets for the purposes of safety and transparency and this may have influenced the behaviour of some drivers. For example, some may have hidden or ended their mobile phone use having detected the observers. Once again, this risk was present in all previous studies.

The mobile phone survey also recorded the use of tablets, mp3 players, and satellite navigation systems, along with any other distracting activity (e.g. eating or drinking) at the end of each observation as a short 'free text' description. Being distracted by using such devices is dangerous and also illegal[18]. It is possible that a few users of these devices are included in the standard observation data where the observer could not clearly tell whether a driver was using a mobile phone or some other device. However, this effect may also be present in the other direction, i.e. observers not recording mobile phone use as they thought it was a different type of device.