PRIMEs design and installation

Design overview

Installing PRIMEs in a consistent manner using the same designs and approach for traffic signs and road markings as that trialled in the Project PRIME research should yield similar positive results to those seen in the PRIME Phase 1 trials. This document has been prepared to assist others to replicate the approach adopted so as to ensure consistent application.

This will hopefully replicate the benefits of PRIMEs based on the research findings and also support motorcyclists from across the United Kingdom with a consistent understanding of PRIMEs in order to recognise their installation on approach to demanding bends.

The PRIMEs consist of two engineering features: the traffic sign and road marking.

The PRIME traffic sign whilst non-prescribed was designed to be consistent with features of the TSRGD. The shape and colour scheme is consistent with other signs providing information to road users and the motorcycle legend used in other sign details was adopted. The traffic sign design and dimensions are included in Appendix E.

The PRIME road marking is a series of three truncated chevrons positioned on the approach to a bend. The intention is that the markings encourage motorcyclists to ride ‘through the gap’ and act as a cue for riders to adjust their speed, position and braking behaviour.

Two versions of the PRIME road marking were used depending on the lane width. The PRIME road marking design and dimensions used are included in Appendix F.

The distance between each of the three PRIME road markings was always set out equally. However, at some sites the overall distance for all three PRIME markings was decreased or increased based on motorcycle approach speed and any prior bends.

Before any road trials were conducted, rider and driver interviews were undertaken to assess levels of acceptance of the PRIMEs concept and understanding of the traffic sign and road markings. The results indicated that when the traffic sign was presented before the road marking (as would be experienced on the road) the understanding of the road marking increased from 28% to 79% which was taken as good evidence for using the traffic sign with the road marking. It may be that later research will identify that the sign or road marking could be used individually. Until that research is undertaken it is recommended that bends treated with PRIMEs utilise both road markings and sign.

Design process

The PRIME design process is set out in five stages covering speed surveys, establishing the PRIME traffic sign and road marking positions, site visit and installation. These are described in more detail below to assist roads authorities who wish to install PRIMEs.

Step 1 – Motorcycle Speed Surveys

Whilst not essential, it is suggested that motorcycle speed measurements are undertaken at potential PRIME sites as this has a direct bearing on the layout of the PRIME markings and signs. Ideally the speed measurement should be undertaken on the direct approach to the bend and within approximately 90m of the commencement of the bend (see: Figure 1). The point 90m in advance of the bend is where the PRIME markings will be sited is therefore the ideal location where a speed survey can be undertaken if feasible.

Various survey methods are available but the more inconspicuous the less they are likely to influence existing rider behaviour. Where possible, a true unimpeded representation of motorcyclist approach speed is best.

Step 2 - Establishing the PRIME traffic sign position

Two factors determine the position of the PRIME traffic sign:

• The position of the first PRIME road marking that a motorcyclist will encounter on approach to the bend. This is the datum point for setting out the PRIME traffic sign.
• The sign should be located in advance of the first PRIME road marking in accordance with Traffic Signs Manual Chapter 4 Appendix A ‘Sizes of Warning Signs and Siting Details’ (TSM). This ensures that the sign is visible to approaching motorcyclists and they have sufficient time available to anticipate the PRIME road markings ahead.

As shown in the TSM, the distance the PRIME traffic sign is measured from is the first PRIME road marking encountered by motorcyclists. The distance required is determined by the approach speed of motorcyclists. This information will have been determined from the previously detailed speed measurements. 

Local site constraints and topography may have an impact on the final location of the PRIME traffic sign. It is not critical that the PRIME traffic sign is situated within view of the PRIME road markings. It may be positioned in advance of a bend prior to the road markings. The most important factor is that the PRIME traffic sign has clear forward visibility to it.

The PRIME traffic sign itself is a standard size, which does not vary depending upon the approach speed of motorcyclists or other traffic. The signposts used in the PRIME trials are passively safe and have been selected for conditions experienced in Scotland. It is recommended that the roads authority select a suitable signpost based on their own experience and procedures.

Step 3 - Establishing the PRIME road marking position

Identifying the position of the PRIME road marking at the bend is critical to the success of the PRIMEs. The initial dimension required for setting out PRIME road markings and the sign is the distance of the PRIME road marking from the tangent point of the bend (shown as ‘B’ in Figure 1). The PRIME research has identified that this distance varies depending upon the recorded approach speed of motorcyclists before the use of PRIMEs. 

Generally, where motorcyclists approach a bend at speeds less than 50mph ‘PRIME Marking 3’ is required to be closer to the start of the bend. Conversely where approach speeds generally exceed 50mph, ‘PRIME Marking 3’ should be sited further back from the bend. The approach speed of motorcyclists also determines the spacing between ‘PRIME Marking 1, 2 and 3’ (see below). 

For a lower approach speed of 50mph and less, it is recommended ‘PRIME Marking 3’ is sited in the range of 15m to 25m from the commencement of the bend and the spacing between ‘PRIME Marking 1, 2 and 3’ is between 20m to 25m. The spacing between the ‘PRIME Marking 1, 2 and 3’ should always be equal.

For a higher approach speed greater than 50mph it is recommended that ‘PRIME Marking 3’ is sited in the range of 25m to 35m from the commencement of the bend and the spacing between ‘PRIME Marking 1, 2 and 3’ is 30m. The spacing between the ‘PRIME Marking 1, 2 and 3’ should always be equal.

It is possible there will be other road markings on the road on approach to the chosen PRIME bend (such as ‘SLOW’). In this case the placement of the PRIME road markings can be adjusted as part of the design to make sure there is no overlap or conflict. Similarly the presence of previous bends or nearby access/junctions may require an adjustment in the PRIME design and/or spacing to achieve the optimal locations. In the research trials, the spacing was not adjusted below 20m spacings and for consistency this is considered the minimum.

If speed surveys are conducted, it is suggested that the 85th percentile speed be measured on the approach to the bend where the PRIME markings are to be installed. This would typically be up to 90m from the commencement of the bend (See Figure 1, distance A).

Where the 85^th percentile speed of motorcycles on approach to the bend is up to 50 mph the distance from the start of the bend to the closest PRIME marking (PRIME marking 3) (shown as B above) will be 15 to 25 metres. The PRIME spacing (shown as C above) will be 20 to 25 metres.

Where the 85^th percentile speed of motorcycles on approach to the bend is over 50 mph the distance from the start of the bend to the closest PRIME marking (PRIME marking 3) (shown as B above) will be 25 to 35 metres. The PRIME spacing (shown as C above) will be 30 metres.

In both scenarios the distance from PRIME marking 1 to the PRIME sign will be in accordance with Traffic Signs Manual Chapter 4 Appendix A ‘Sizes of Warning

The PRIME road markings are a series of three pairs of truncated chevrons and are positioned towards the centreline of the approach lane to the bend for a left-hand bend. On the approach to a right-hand bend the PRIME markings are positioned towards the edge line. 

It is important to retain a gap between the PRIME road marking and the carriageway centre or edge line so it is clear to motorcyclists that they are approaching a PRIME marking and there is an area on the lane free of road marking material.

To allow PRIMEs to be installed on narrower roads an alternative marking is available which conveys the same message but is a shorter length than the standard marking. This shorter marking is used when the lane width is 3.5m or less.

The PRIME road marking material selected for use by Transport Scotland in Project PRIME was a permanent tape marking (3M Stamark A380 ESD). This material is a factory product which meets specifications set out in BS EN 1436. It offers a high value of skid resistance, has a high level of retro-reflectivity and luminance which is important for conspicuity in all conditions. As the product is a structured material it also allows surface water to pass over its profile whilst not allowing water to sit on the material where motorcyclists would be riding over it. Other high performance road markings may be available with similar characteristics and may therefore be suitable for PRIMEs application.

Motorcyclists are often concerned about the grip of traditional road markings (i.e. white paint). By using a permanent tape marking with a high grip this should reduce concerns from motorcyclists about riding over the tape marking. 

If a tape marking is proposed, particular care should be given to follow the manufacturer and supplier installation guidance to ensure the tape is secured to the road surface. This will reduce the possibility of premature failure of the product from taking place.

Step 4 – Chosen PRIME Bend Site Visit and Concluding the Design Process

Prior to installation of the PRIME road markings and signs a site visit will allow the opportunity to review the chosen locations to ensure appropriateness.

For the Transport Scotland PRIME Trials, the Design Team installed roadside wooden posts on the verge to mark out where the PRIME traffic sign and three PRIME road markings would be installed. These were easily adjusted and enabled the Design Team to review the traffic sign and road marking positions for suitability and to ensure that no conflicts were present, such as road surface defects, visibility, etc.

If possible, having expert/staff motorcyclists available to ride through the bends is a benefit as they can provide valuable feedback on the approach characteristics of the bend where PRIMEs are to be installed. However, if roads authorities are unable to arrange site rides by motorcyclists this should not preclude the use of PRIMEs.

Once the marking up of the traffic sign and road markings is agreed, temporary spray markings can be applied on the verge next to the posts allowing the posts to be removed from the site. Measurements can then be taken of the exact layout for non-prescribed signs applications.

In order to adhere to best practice the guidance contained in the General Principles and Scheme Governance General Information (GG119) of the Design Manual for Roads and Bridges (DMRB) was followed. Stage 1/2 and Stage 3 Road Safety Audits were undertaken for each installation on the Scottish Trunk Road Network. If required, designers should follow the relevant Road Safety Audit procedure used by the Overseeing Organisation for their own PRIMEs installations. It may be beneficial if at least one member of the Road Safety Audit team has experience of motorcycling.

As the PRIME road marking and traffic sign are not approved signs within the TSRGD, they required Non-Prescribed Signs (NPS) approval from the respective Overseeing Organisation.

Approval for their use on the Scottish Trunk Road Network had to be sought from Scottish Ministers on a site-by-site basis with Non-Prescribed Signs approval gained for every individual PRIME site using the Application for Authorisation of Non -Prescribed Traffic Signs and Special Directions 2016. Other road authorities in Scotland follow the same process and procedure, and submissions should be sent to:

non-prescribedsigns@transport.gov.scot for consideration. Any deviation from the layout shown in a non-prescribed signs authorisation may mean the PRIME marking is not authorised.

Outwith Scotland, designers should follow the relevant procedure for having non-prescribed signs and road markings approved through their respective Overseeing Organisation.

Once the design process is concluded, including any Road Safety Audits, Non-Prescribed Signs approval or any other road authorities specific requirements, the chosen PRIME bend sites can progress to the installation phase.

Step 5 – Installation

Installation of the PRIME traffic sign and road markings is a simple engineering measure which should be routine for roads authorities and their contractors.

Experience has shown that the road markings for three or four PRIME sites can be achieved in a single day, but this will be determined by the geographic location of the sites. The installation of the PRIME traffic sign should also be achievable in a short period of time, typically a foundation and post installation could be completed in a single day with the sign erected on the post on a subsequent day.

To aid setting out of the road markings, it may be possible to make a simple template for the PRIME road markings off-site, which can then be used on site to speed up the installation process and reduce the time required on site. This reduces road worker exposure to potential harm on the road and disruption to the travelling public caused by traffic management operation.