Discussion

Without counting the comparison sites where no statistically significant effects were observed, or carry-over sites where no PRIME road markings were installed, 61.9% (i.e. 78 out of 126 possible results across all 3-years of road trials) indicated a statistically significant effect or positive trend for rider behaviour due to the installation of PRIME road markings. These can be broken down into 50.8% that were statistically significant (i.e. 64 out of 126 possible results) and a further 17.9% indicated positive trends in the data (i.e. 14 out of 126 possible results).

As with Phase 1, there were no instances of statistically significant increases in speed, dangerous positioning, or decreased use of the PRIME gateways. However, for the first time in the research, increases in braking were observed at one site (Rob Roy’s Dip East 1) and this is discussed below. Taken together these observations suggest that PRIMEs did not have a detrimental impact on rider behaviour. At sites where statistically significant changes were not observed, results were broadly consistent with sites where PRIMEs were not installed. As such, there could be benefits of PRIMEs at these locations which were not sensitive enough during statistical analyses to illustrate significant effects and where further research could provide greater insights into rider behaviour.

Speed, position, braking and use of final PRIME road marking

A discussion of the results for speed, position, braking and use of the final PRIME gateway road marking is presented below.

Speed

In Phase 2 there were a mix of bend types (i.e. both left-hand the right-hand bends). Some were approached from long straight sections of road where motorcyclists were more likely to be carrying speed into the bend (i.e. Butterbridge, Rob Roy’s Dip East 1 and 2, Mid Lix). In addition, some of the approaches (i.e. Glenogle, Dalchonzie) were on undulating or downhill sections that could have exacerbated the issue of carrying speed into the bend. Other trial sites were more technical and involved more complex bends and limited views around the bends (i.e. Loch Lubhair East, Dunira East).

Statistically significant speed reductions ranged from 1.85mph to 4.89mph when PRIMEs had been installed. Previous research has indicated long-term speed reductions of 3kmh (1.86mph) to 4kmh (2.49mph) for all vehicle types when PCMs were installed (Martindale and Urlich, 2010), and these results would seem to support that finding. However, it is not clear what the speed profiles for motorcycles were from Martindale and Urlich’s research.

Speed data across the PRIME road trial sites were within the prescribed speed limits and comparable with national data indicating an average free-flow motorcycle speed of 51mph (Department for Transport, 2015). In Scotland the average speed of motorcycles on national speed limit single carriageways is 60mph (Transport Scotland, 2021).

In this research, across the three years, the fastest average speeds were observed at Butterbridge East (57.1mph), and Butterbridge (55.9mph). This was perhaps expected as Butterbridge East was a fast straight section and Butterbridge was preceded by a fast downhill section. The slowest average speeds across the three years were observed at Glenogle (34.52mph), and Dalkenneth (40.7mph) which were some of the more technically demanding bends investigated.

In general, and in line with Phase 1 results, the speed reductions were sustained across PRIME 2 weekend data collection periods. This provides evidence that PRIMEs have an effect beyond their initial installation. In previous research the effects of PRIMEs have been demonstrated over a 1-year and 2-year period (Stedmon, 2022).

Position at final PRIME road marking and apex of the bend

In previous research, speed reductions have tended to be relatively modest with lane keeping more reliably influenced (Stedmon et al, 2021, 2022, 2023).

This provides evidence that PRIMEs influenced rider position across a range of bends. In addition, where significant effects were observed they were sustained throughout all the PRIME data collection weekends and showed that PRIMEs had a lasting effect at these locations.

For motorcycle position at the apex of the bend, statistically significant effects were observed across 14 of the 18 trial sites. This indicated positive changes in road position with riders taking a wider line around both left-hand and right-hand bends.

These results provide strong evidence that PRIMEs continued to influence rider position after the final PRIME road marking and through the bend itself (i.e. where no PRIMEs were installed). In all cases the effects were sustained over the PRIME data collection weekends.

Braking

While braking was one of the key variables measured in the PRIME road trials, this was not a high incidence activity with very little braking recorded at some sites. This was similar to the findings in Project PRIME: Phase 1 (Stedmon, 2020, 2021, 2022). The low incidence for braking, in itself, can be viewed as a positive observation. It can be dangerous for motorcycles to initiate braking on a bend as this behaviour can destabilise the motorcycle which then tends to become more upright and travel in a straighter direction going forward. This often accounts for motorcyclists losing control on bends. Research has shown that motorcyclists tend to brake first on a bend before adjusting their steering but will tend to swerve first on a straight road before braking (Stedmon, Crundall, Crundall, Irune, Saikayasit, van Loon and Ward, 2010).

Trends were observed at Glenogle (total braking), Dalkenneth (braking on the bend), West Lodge (braking on the bend) and Loch Lubhair East (braking on the bend) and Dalkenneth (braking on the bend).

A finding that was not expected was a statistically significant increase in braking at Rob Roy’s Dip East 1 for braking late, braking on the bend, and total braking. What appears to be the case is that there were more instances of braking in the 2025 3 PRIMEs dataset across each measure of braking even though no change had been made to the trial site since the 2020 3 PRIMEs data were collected.

Given that this is the only site over the course of the six-year project where an increase in braking has been observed, it may illustrate the sensitivity of analysing low incident behaviour. This is where the knowledge base built up over the last six years, provides some confidence in knowing that where no material changes were made to the trial site it may be anomalous and there is insufficient data to explore it further.

Of these trial sites, West Lodge was a fast approach from a straight into a sharp left-hand bend. It might have been expected that motorcycles could be carrying excess speed into bends and so a significant reduction in braking at this site was a positive outcome of installing PRIMEs. For Glenogle, the approach was slower and more technical but even so the reduction in braking at this site was also a positive outcome.

Use of the final PRIME road marking

This provides strong evidence that motorcyclists were riding ‘through the gap’ at the final gateway marking and therefore in the desired position prior to the bend. These effects were observed throughout the PRIME data collection weekends illustrating sustained effects.

These findings are in line with those from previous years of Project PRIME. Across all 35 PRIMEs trial sites (2020 to 2025) there has been a statistically significant uptake in the use of PRIMEs at 30 trial sites and trends for increased uptake at four trials sites. This demonstrates that overall positive behaviour change has been observed at 34 of 35 trials sites for increased use of the final PRIME road marking.

Overall, PRIMEs had a range of effects on speed reduction, lane position, braking and use of the final PRIME road marking. Taken together, these trials provide strong evidence that PRIMEs have a positive effect on rider behaviour. Combined with the Phase 1 results this year’s results add further evidence for PRIMEs influencing road position both at the final PRIME road marking and also through the bend itself.

“Carry over” effects of PRIMEs

For 2024 an additional research question was whether PRIMEs might demonstrate behaviour change on right-hand bends. As an additional investigation there was the opportunity to collect data from two bends (left-hand then right-hand) which immediately followed one right-hand bend trial site (Dunira East) in order to assess any carry over effects. While the PRIME road sign and road markings were installed at the trial site (i.e. Dunira East) the following two bends did not receive any installations.

Results indicated that there were significant reductions in speed across all three bends, positive changes in position at the final PRIME road marking (or where it would have been) for Dunira East and Carry over Right; and a positive change in behaviour for position at the apex on the first PRIME weekend for Carry over Right. Across Dunira East and Carry over Right there was a significant uptake in PRIMEs gateways and a trend for Carryover Left. While the results are not conclusive and only apply to one site, they provide a valuable insight into potential benefits of PRIMEs beyond immediate bend installations.

Long-term effects of PRIMEs

Transport Scotland provided funding for additional research in 2025 to investigate the nature of potential long-term effects for PRIMEs at the trial sites. With only one new site (Butterbridge East) installed there was an opportunity to return to existing trials sites and investigate long-term behaviour change by comparing results from 2025 with previous years.

It was therefore possible to compare behaviour across 5-year, 3-year and 2-year intervals as outlined in Table 6. A decision was made to focus on sites from 2020 in order to extend the long-term comparison or 5 years across half of the sites.

Table 6: showing details of PRIME sites utilised to analyse sustained effects

Site name	Previous data collection year	Long term intervals
Butterbridge East (new site)	n/a	n/a
Butterbridge	2022	3 years
Loch Lubhair East	2020	5 years
Rob Roy's Dip East 1	2020	5 years
Rob Roy's Dip East 2	2020	5 years
Dalkenneth	2023	2 years
Tullybannocher (comparison)	2024	1 year

The results indicated that statistically significant long-term behaviour change for position at the final PRIME road marking was observed at four of the five existing sites (80%). At the apex of the bend, riders took a wider line around the bend at three trial sites (60%). Sustained reductions in braking were only observed at one site (20%) but this illustrated a long-term behaviour change over a 5-year period. For use of gateways, long-term behaviour change was observed at all the existing trials sites (100%). These results are summarised below (Table 7).

Table 7: Showing details of long-term behaviour change observed

Site name	Time period	Speed	Position at final PRIME	Position at Apex	Braking	Use of PRIMEs
Butterbridge East (new site)	n/a	No	No	No	No	No
Butterbridge	3 years	No	Yes	No	No	Yes
Loch Lubhair East	5 years	No	Yes	Yes	Yes	Yes
Rob Roy's Dip East 1	5 years	No	Yes	No	No	Yes
Rob Roy's Dip East 2	5 years	No	Yes	Yes	No	Yes
Dalkenneth	2 years	No	No	Yes	No	Yes
Tullybannocher (comparison)	n/a	No	No	No	No	No

Speed reductions - 5 PRIMEs v 3 PRIMEs

Only two trial sites observed a reduction in speed due to the installation of 5 PRIMEs (i.e. Loch Lubhair East and Rob Roy’s Dip East 2). These were both of the tight format (i.e. in between the original 3 PRIMEs formation). No reductions in speed were found at the trial sites that had the extended 5 PRIMEs format. No other significant effects were observed for other behaviours (Table 8).

Table 8: Showing key results observed for 5 PRIMEs formats

Site name	Speed	Position at final PRIME	Position at Apex	Braking	Use of PRIMEs
Butterbridge East (new site)	No	No	No	No	No
Butterbridge	No	No	No	No	No
Loch Lubhair East	Yes	No	No	No	No
Rob Roy's Dip East 1	No	No	No	No	No
Rob Roy's Dip East 2	Yes	No	No	No	No
Dalkenneth	No	No	No	No	No
Tullybannocher (comparison)	No	No	No	No	No

Overall, this indicates that 5 PRIMEs did not have much of a benefit over installing 3 PRIMEs. However, for some locations where the tight 3 PRIMEs format might be appropriate, two of the three trial sites have shown a speed reduction. It is possible that the tight formation of 5 PRIMEs creates a more conspicuous visual cue to an approaching motorcyclist over an extended format, where a rider might be looking ahead of gateways that are spaced out more. The tight formation might provide to stronger cue in a shorter space on the road.

Dry weather v wet weather

In 2025 one of the two Baseline data collection weekends had very poor weather and with this opportunity, it was decided to collect data on two consecutive weekends in order to make comparisons between dry weather and wet weather riding behaviour.

Overall, speed was significantly reduced in wet weather at four trial sites (and a trend observed at another); position at the final PRIME changed on right-hand bends in the wet weather; riders positioned themselves closer to the apex at one trial site and there was a reduced use of PRIME gateway in wet weather at one site with a trend at another. These observations are presented below (Table 9).

Key

Yes denotes a change in behaviour was observed.

Trend denotes a trend in data

Table 9: Showing key results for wet weather

Site name	Speed	Position at final PRIME	Position at Apex	Braking	Use of PRIMEs
Butterbridge East (new site)	Trend	Yes	No effect	No effect	Trend
Butterbridge	Yes	No effect	No effect	No effect	No effect
Loch Lubhair East	Yes	No effect	Yes	No effect	No effect
Rob Roy's Dip East 1	Yes	Yes	No effect	No effect	Yes
Rob Roy's Dip East 2	Yes	No effect	No effect	No effect	No effect
Dalkenneth	No effect	No effect	No effect	No effect	No effect
Tullybannocher (comparison)	Trend	No effect	No effect	Trend	No effect

This investigation can only be treated as a preliminary investigation into the effects of weather as it is difficult to compare sites over a large geographic area consistently in terms of amount and length of time rainfall occurred and other accompanying environmental effects such as wind strength and direction, level of exposure for each site to the elements, and even how close they are to rest areas for riders.

Rider profiles across Project PRIME

The previous findings from Project PRIME illustrate a consistent profiles of lead, pillion and group motorcyclists that across the years (Table 10).

Table 10: Showing motorcycle profiles across the PRIME road trial sites

Year	Total	Lead %	Pillion	Group
2020	12,949	31.25	11.13	63.09
2021	9,594	26.25	9.76	56.93
2022	9,670	34.37	9.35	61.40
2023	4,652	33.15	7.01	57.14
2024	5,196	40.69	8.24	56.68
2025	5,709	35.45	7.72	58.98

Of the total motorcycles across the six years (N=47,770) typically around 10% (N=4,476 mean=9.37%) carried a pillion, approximately one-third (N=15,599 mean=32.65%) were lead motorcycles and just under two-thirds (N=28,538 mean=59.74%) were traveling in a group. This meant that motorcycle distributions remained similar throughout the project.

Project aims and objectives

The key aim of this phase of the research has been to conduct further research to consolidate our understanding of the benefits or drawbacks of installing PRIMEs based on trial site characteristics. This has been addressed through practical objectives to:

• install and evaluate PRIMEs across 18 trial sites and expand the PRIMEs dataset to 40 trial sites and 50,000 motorcycles – by the end of 2025, data were collected at 18 trial sites (13 new trial sites plus 5 sites used in previous years’ research) and two comparison sites. In total, 47,770 motorcycles were observed by the end of Phase 2. While not reaching 50,000 motorcycles this reflects the opportunistic nature of the sample.
• address specific research questions for: untreated roads, right-hand bends, and further reductions in speed – each year during Phase 2 these specific research questions were investigated. These have been detailed in each year’s technical reports and integrated in this summary report.
• conduct a meta-analysis to provide guidance on identifying sites where PRIMEs might be beneficial or not – as part of earlier Phase 2 work (outside of RST funding) with the development of the Installation Toolkit, a thematic analysis of bend characteristics was conducted to provide insights into which bends might benefit the most from PRIMEs and also those that may not. The findings from Phase 2 will be considered in any update of the Installation Toolkit so that practitioners can make informed decisions about installing PRIMEs at their own proposed locations
• use Human Factors participatory methods to promote wider acceptance of PRIMEs by motorcyclists and other road users – this has been developed through informal outreach activities and also through public engagement activities throughout Phase 2
• feedback and disseminate results to Government ministers, road safety stakeholders, academia and riders themselves – Project PRIME has been able to disseminate research findings throughout Phase 2 to a variety of professional interest and stakeholder audiences
• provide substantive evidence beyond Phase 1 of site characteristics and benefits of PRIMEs at different locations – through the expanded scientific knowledge for PRIMEs generated through Phase 1 and Phase 2, conference/stakeholder presentations and scientific journal papers, there is now a substantial peer-reviewed and academically accepted basis to the science behind PRIMEs.

The Safe System approach to motorcycle casualty reduction

Transport Scotland recently published its ‘Road Safety Framework to 2030′ outlining a long-term goal for road safety where no-one dies or is seriously injured by 2050 (Transport Scotland, 2021). It proposes a ‘Safe Systems’ approach to road safety delivery as set out in the National Transport Strategy Delivery Plan (Transport Scotland, 2020). In relation to the concept of PRIMEs, the current research addresses the following pillars:

Safe speeds

speed limits in a Safe System are designed for crash-avoidance and reducing physical impact. Key factors that should be taken into account in any decisions on local speed limits are: history of collisions, road geometry and engineering, road function; composition of road users (including existing and potential levels of vulnerable road users); existing traffic speeds, and road environment (Transport Scotland, 2021). With these factors in mind, PRIMEs offer a potential tool for supporting speed limits where roads have already been brought up to the best possible standard. With the observed reductions in speed and no statistically significant increases in speed, PRIMEs may therefore provide a means for maintaining safe speed limits rather than drastically reducing them. However, coupled with improved position on the road and reduced braking on bends this would appear to be supporting the rider experience more holistically rather than focusing on one specific measure of performance for safety.

Safe road use

Road users should pay attention to the road ahead and the task in hand; adapting to the conditions (weather, the presence of other users, etc.); travel at lower speeds; and give sufficient room to all other road users, no matter what their mode of travel (Transport Scotland, 2021). PRIMEs may provide motorcyclists with a tool that allows them to adapt their behaviour to the road environment and which other road users may also use as a cue for demanding bends and the presence of motorcyclists. In this way PRIMEs may help ensure that road users are risk-aware, can develop coping strategies for demanding situations, and act appropriately to keep themselves and others safe on the road (Transport Scotland, 2021). This was demonstrated by the positive results for road position both at the final PRIME road marking and at the apex of the bend.

Safe roads and roadsides

The environment is designed to reduce the risk of collision and to mitigate the severity of injury should a collision occur. This can be achieved through design, maintenance and the implementation of strategies to reduce casualties on the roads (Transport Scotland, 2021). This can also be promoted through positive behaviours and safer sharing of spaces, the appropriate use of speed limits and signage that provides a much more affordable and sustainable way to protect the most vulnerable road users. PRIMEs provide a low-cost and easily maintained casualty reduction initiative working in harmony with other interventions such as bike-guard and other vehicle restraint system (VRS) solutions. They can be installed on existing roads quickly and efficiently or incorporated into road upgrade schemes. From the low incidence of braking across the trial sites, this would seem indicate that motorcyclists are generally set up well for these bends but that other effects on position and speed enhance safety further.

Across these strategic pillars PRIMEs have the potential to provide a new and unique contribution to a ‘Safe System’ approach. There is clear evidence from the research conducted over the last 6-years that PRIMEs positively influence rider behaviour and it is important to begin planning for an implementation phase of work that will underpin the roll-out of PRIMEs more widely. With local authorities across Scotland and the rest of the UK expressing an interest in installing PRIMEs the scope of the project is already increasing.