Method and analyses

This research was conducted as a quasi-experiment and combined elements of field observation with formal experimental design (Lehman, 1991). This approach allowed for conventional ‘pre- and post-intervention’ assessment to be conducted so that any effects of the PRIMEs on riding behaviour could be determined against the baseline measures. This approach has been used in similar research of this kind (Fildes et al, 2005; Mackie and Scott, 2015; Hirsch et al, 2017, 2018; Stedmon, McKenzie, Langham, McKechnie, Perry and Wilson, 2021, 2022, 2023; Winkelbauer et al, 2021).

Participants

This research relied on an opportunistic sample of motorcyclists. Across all the trial sites 15,557 motorcycles were observed and from these 5,680 lead motorcycles were analysed in more detail.

Apparatus

Data were captured at each site using small and inconspicuous weatherproof video cameras typically attached to roadside posts or trees (Figure 5).

Two images of roadside PRIMEs trial sites. On the left a video camera is attached to a tree. On the right, a video camera is attached to a post.
Figure 5: Images showing cameras attached to trees or roadside posts

The cameras captured 1080p video at 60Hz for time periods of at least 20hrs, stored in 512Gb microSD cards. Power-packs were used to collect continuous data through the data collection periods.

At each site, three cameras were installed facing: towards the rider, behind the rider and perpendicular to the rider a short distance ahead of the last PRIME road marking (Figure 6).

Diagram showing camera positions at each trial site, as described in text
Figure 6: Image showing camera positions at each trial site

The road markings were installed using 3MTM StamarkTM High Performance 100 mm wide permanent tape. This material was chosen because it provided increased visibility, grip and safety, even in the wet. It had also been used in previous research (Bricelj, Merkun, Brumec and Hudej, 2016). The material also offered high levels of adhesion to the road surface and provided a permanent marking that would not be disturbed by other vehicles (i.e. general traffic and heavy goods vehicles).

Design

The independent variable in this research was the PRIME road markings which had two levels, Baseline (without PRIMEs installed) and PRIME (with PRIMEs installed).

In 2023 and 2024 baseline and PRIME data were collected on a number of occasions, as specified below:

  • Baseline 1 and 2 – two separate weekends before PRIMEs were installed
  • PRIME 1 – the weekend after PRIMEs were initially installed
  • PRIME 2 – three to four (2023) or six or eight (2024) weeks after the PRIME 1 data collection

In 2025 the key research question was whether PRIMEs could promote further speed reductions beyond previous results. By re-visiting trial sites where speed reductions were not apparent, it was possible to investigate if installing different PRIME gateway road marking formats could provide a stronger cue for riders to reduce their speed.

It was decided to investigate the potential for installing 5 PRIMEs instead of 3 PRIMEs at the trial sites that were selected for 2025. Two formats (‘tight’ or ‘extended’) were developed depending on the characteristics of the approach to the bend where the original 3 PRIMEs had been installed (Figure 7).

Image showing the ‘tight’ and ‘extended’ 5 PRIME design formats, as described in text
Figure 7: Image showing the ‘tight’ and ‘extended’ 5 PRIME design formats

For bends where less road space ahead of any preceding bend might compromise the installation of the extended design, the tight format was used. This design allowed for the placement of two additional PRIME road markings in between the original 3 PRIMEs (left format in Figure 10). For bends with more road space ahead of any preceding bend the extended format was used. This design allowed for the placement of two additional PRIME road markings in advance of the original 3 PRIMEs (right format in Figure 10).

This selection of trial sites provided a 4:2 split for left-hand vs right-hand bends but more importantly a 3:3 split for tight and extended formats for 5 PRIMEs. It was decided to revisit Tullybannocher (the comparison site from 2024) as that would provide an opportunity to compare data for overall behavioural consistency at a site where no PRIMEs were installed.

The bends that were selected for the 2025 trials are detailed below (Table 2).

Table 2: Showing proposed PRIMEs designs for trial sites
Site name Classification from the toolkit Direction 85th% speed range (mph) Proposed PRIME design
Butterbridge East Fast flat from a straight Right n/a (new site) Extended
Butterbridge Fast downhill from a straight Left 55.9 Extended
Loch Lubhair East Fast flat from a bend Left 53.7 Tight
Rob Roy's Dip East 1 Slow flat from a straight Right 47.1 Extended
Rob Roy's Dip East 2 Fast downhill from a bend Left 51.6 Tight
Dalkenneth Slow flat from a bend Left 40.7 Tight

To provide for a comparison between the 5 PRIME design formats trialled in 2025 the data collection was undertaken as specified below.

For sites where new 5 PRIME installations were made

  • Baseline 1 – baseline data collection without PRIMEs installed
  • Baseline 2 – baseline data collection without PRIMEs installed
  • 3 PRIMEs NEW – data collection the weekend after 3 PRIMEs were installed
  • 5 PRIMEs – data collection the weekend after 5 PRIMEs were installed

For sites where the 5 PRIME installations were added to the existing 3 PRIME installations:

  • 3 PRIMEs OLD – baseline data collection with previous 3 PRIMEs
  • 3 PRIMEs OLD – baseline data collection with previous 3 PRIMEs
  • 5 PRIMEs – data collection the weekend after 5 PRIMEs were installed
  • 5 PRIMEs – data collection the weekend after 5 PRIMEs were installed

Note: In 2025 any existing PRIME markings were re-instated at the time of 5 PRIME installations to ensure consistency of appearance with existing markings.

With this approach any effects of PRIMEs on riding behaviour could be determined against the baseline measures.

A range of dependent variables were identified to capture data about the potential influence of PRIMEs on rider behaviour (Table 3).

Table 3: Table showing dependent variable and associated measures
Dependent variable Measure (units) Apparatus Reason
Speed Miles per hour (mean, standard deviation, mode, 85th %tile) Side facing camera to measure speed between two points (i.e. 10m apart) To assess any changes in speed due to PRIMEs
Position Lateral lane position at the final PRIME and at the apex (mean, standard deviation, median, mode) Forward-facing camera to measure lateral position on approach to the bend. Rear-facing camera to measure position at the apex To assess any changes in lateral lane position due to PRIMEs
Braking Brake light illumination (count) Rear-facing camera to capture brake light illumination To assess any changes in braking on bends due to PRIMEs
Motorcyclists Pillion, lead, group riders (count) From video data collected for other measures To identify rider characteristics
Use of PRIMEs Use of the final PRIME (count) From video data collected for other measures To identify how many riders used PRIMEs

Procedure

Prior to data collection, trial sites were assessed for suitability ensuring that any extraneous variables were controlled as much as possible so that they would not otherwise influence rider behaviour (e.g. poor road surface, obscured views, potholes, poor safety provisions).

Comparison sites were selected that were of a similar standard and did not require engineering works.

The weather during the trials was generally poorer than that experienced in Phase 1 with use being made of contingency weekends where necessary. If light rain showers occurred, the data were generally included for analyses. Only if the showers were heavy and caused wheel spray or if other vehicles had their windscreen wipers operated was the data excluded from analyses.

Data were captured during the typical motorcycle season (i.e. May to September). Weekends were chosen as this was generally when motorcyclists ride for leisure/social purposes.

Each weekend cameras were set up at every trial site and recorded all road traffic during Saturday and Sunday from 09:00 to 17:00. Power supplies were replenished through the weekend, and cameras were collected on Sunday evenings.

Care was also taken to make sure that no changes to the sites were undertaken during the pilot trials (i.e. scheduled road works).

Ethics and risk assessment

An independent review of potential ethical issues was conducted by Dr Martin Langham who acted as an external auditor for the project. Approval was granted in accordance with general principles of the British Psychological Society and International protocols.

A risk assessment was also conducted in order to safeguard the research activities. Induction training was undertaken so that roadside safety protocols were adhered to, and the correct PPE was worn at all times.

The design for the PRIME road markings and road sign went through a formal application process for authorisation of non-prescribed traffic signs (Road Traffic Regulations Act 1984: Sections 64 and 65). Approval was granted prior to the trials taking place. Following on from this, independent road safety audits were conducted in accordance with the Design Manual for Roads and Bridges (DMRB) to oversee the safe installation of PRIMEs at all trial sites.

For more details on the method and analyses, please refer to Stedmon, McKenzie, Langham, McKechnie, Perry and Wilson (2021, 2022).

Data analyses

Once the data had been processed, they were then analysed in a number of ways.

Initially Baseline 1 and Baseline 2 datasets were compared by conducting a T-Test (t) to identify any differences between them. Where any significant differences were observed, effect size was calculated using Cohen’s (ds) equation.

Where the Baseline 1 and Baseline 2 datasets were observed to be the same (i.e. there was no significant difference) they were combined into a single dataset (i.e. ‘Baseline’). Where any difference was observed, Baseline 1 and Baseline 2 were kept as separate datasets and compared individually with the PRIME 1 and PRIME 2 datasets.

Speed and lateral position data were analysed using one-way Analysis of Variance (ANOVA) techniques. Where any significant results were observed, effect size was calculated using a partial eta squared (η2) analysis. Post-hoc Bonferonni-Hoch analyses were conducted in order to determine where significant differences occurred between the datasets. Tests for effect size were conducted using Cohen’s (ds) calculations.

Braking behaviour and use of PRIMEs datasets were analysed using Chi Square (X2) tests. Where any significant results were observed, effect size was analysed using Cramér’s V (V) calculations. Further post-hoc analyses were performed by calculating standardised residuals in order to determine where significant differences occurred between the datasets.

For detailed statistical analyses for each site please refer to Stedmon, McKenzie, Langham, McKechnie, Perry and Wilson (2023, 2024, 2025).