Temporary Road Markings: Working Group Findings, April 2003

Contents

1. Introduction

2. Temporary Traffic Management Design and Specification

3. Road Surface Types

4. Application and Removal

5. Regulation and Approval Issues

6. Summary

7. References

The members of the Temporary Road Markings Working Group were:

This document, Temporary Road Markings: Working Group Findings, is published on behalf of this group by TRL Ltd.

Hard copies are available from info@trl.co.uk for the price of £15 including postage.

Temporary Road Markings: Working Group Findings, April 2003

1. Introduction

At major road works, road markings often need to be removed or masked and temporary markings provided. Temporary markings associated with the provision of speed cameras can also be required at road works. The ease and success of the application, removal and the durability of temporary road markings has always been subject to the nature of the road surface and the weather conditions. However, recent developments in surfacing materials have added another level of complexity to these processes. The new EU Standard on marking materials has also complicated the specification of products.

In response to these concerns, a working group was convened comprising representatives from the Highways Agency, Department for Transport, Traffic Management Contractors Association (TMCA), Road Safety Markings Association (RSMA), Reflective Equipment Manufacturers Association (REMA) and TRL Ltd. to investigate current issues relating to temporary road markings.

This document deals with the findings of the Working Group and is intended to provide guidance for designers in their choice and specification of temporary road markings, and for practitioners on issues relating to the application, maintenance and removal of temporary road markings at road works.

1. Introduction

2. Temporary Traffic Management Design and Specification

2.1 Road Marking and masking

2.1.1 Options

In choosing the form of temporary markings, account must be taken of the circumstances specific to the project.

Use of each category of temporary marking material is constrained by factors such as weather, temperature and, in particular, the nature of the road surface to which the marking is to be applied. Section 3 discusses road surface types. The specification for each temporary marking material is dealt with in Section 5.

Wherever practical, for the sake of consistency, the category of temporary marking material/product should be continuous in each direction throughout the traffic management layout.

The removal of conflicting road markings can raise issues that need consideration before a product is specified as a preferred option. An example might be the type of road surface to be encountered and whether it may be damaged by a particular removal process. Section 3 deals with road surface types and Section 4.2 deals with the removal of road markings.

The categories of temporary marking material are given in Sections 2.2.1 to 2.2.4 and in Table 1. Masking is dealt with in Section 2.3.1 to 2.3.3 and Table 2.

2.2 Road markings

2.2.1 Hot Applied Thermoplastic Road Markings

Hot applied thermoplastic road markings perform well in terms of durability, conspicuity, speed of application, cost to apply, and skid resistance. This form of marking is used throughout the network as a permanent marking.

However, the removal of thermoplastic markings is slow and can leave a ghosting of the marking and scarring of the surface. If the surface is to be replaced, and there will be no need to remove the temporary marking, then this is not an issue and hot applied thermoplastic should be the preferred option. On new carriageway surfaces, residues are generally unacceptable. The likelihood of residues on negative texture surfaces is higher than on Hot Rolled Asphalt (HRA) because of the tendency for the hot thermoplastic material to run into the voids within the surfacing layer.

2.2.2 Temporary Road Marking Tape

Temporary road marking tape is durable for up to 3 months subject to satisfactory application and offers good conspicuity and skid resistance, though it is comparatively expensive and is slow to apply because of the surface preparation required. White temporary road tapes are available in a variety of widths including 100mm, 150mm and 200mm.

The chief disadvantage of tape is that it will not adhere to the carriageway surface in wet and/or cold conditions. There are particular difficulties with negative texture surfaces; in the wet, the pumping action of the water can cause the tape to lift from the surface even when correctly applied in dry conditions. Temporary tape can be very hard to remove if it is constantly overrun (see Section 4.1.2).

2.2.3 Temporary Reflecting Road Studs

Temporary reflecting fluorescent green/ yellow road studs may be authorised as an alternative to markings for temporary delineation at road works (see Section 5.2 and Chapter 8 of the Traffic Signs Manual, paragraph 3.3.10). These studs are usually approximately 100x50mm (4"x2") and are made from fluorescent green/ yellow high impact polystyrene, with self-adhesive vinyl reflectors. They are especially noticeable in wet night-time conditions when their reflective system gives good guidance. The raised profile of the stud also acts as an audible warning to drivers if over-run.

Temporary road studs are designed to be trafficked but not constantly or heavily over-run, and higher breakages than normal can occur if scheme designs indicate such use.

These studs can be fixed to the road either with a bituminous hot-melt adhesive (hot-melt) or by way of a sticky butyl/bitumen pad pre-fixed to the stud (self-adhesive).

Hot-melt studs stick well to road surfaces but leave a clear mark on the carriageway after removal, so are less appropriate for new surfaces. They adhere well on dry negative texture surfaces but once again, when removed, they leave a mark on the road surface. The road surface can also be damaged when they are removed.

Self-adhesive studs are fast to lay and remove, and leave minimal traces, but are prone to becoming dislodged, particularly if they are used in place of lane lines. On negative texture surfaces in the wet, there can be problems with the self adhesive studs becoming dislodged because of the pumping action of the water, though the application of a glue prior to installation can help (see Section 4.1.3). This is less of a problem with hot-melt studs.

An issue with temporary road studs is their tendency to 'sink' into the surface if constantly over-run, particularly on thin surfaces with higher binder content (see Section 3). This can be minimised by the use of studs with a large (approximately 100x100mm, 4" x 4") footprint. Hot-melt studs seem to sink less than self adhesive, possibly because the hot-melt bitumen fills in the voids in open texture materials.

Temporary studs cannot be masked and therefore must be removed when they are no longer required.

2.2.4 Road marking paint

Paint is generally applied through an airless spray machine, and can be applied at walking pace. As a road marking, with glass reflective beads applied to the surface, it is very effective, with luminance and retroreflectivity comparable with temporary tape. It is also much cheaper than tape or hot applied thermoplastic. However, because of its thinness, paint is less visible than thermoplastic in the wet. It is less durable than hot applied thermoplastic, but this may be less of a concern for temporary applications.

Road marking paint is a good option in the right conditions (see Section 4.1.4), in terms of both cost and performance on an old carriageway where the road surface is to be replaced and there will be no need to remove the marking. The skid resistance of paint can be improved by the application of antiskid material while it is still wet. When used on new carriageways or carriageways that will not be replaced, paint is almost impossible to remove.

Table 1: Road Marking Options (View table)

2.3 Masking

2.3.1 Hot applied Thermoplastic Road Markings

Black thermoplastic material can be effective in masking existing thermoplastic markings. However, in wet conditions the black material can reflect light and appear as a road marking and it is therefore advisable to apply black grit when laying the black material to give a matt finish to its surface. When additional thermoplastic or paint is used for covering or reinstating existing markings, care must be taken to ensure that the total thickness of the marking does not exceed 6mm.

It is practically impossible to completely re-expose the white thermoplastic marking once it has been overlaid by black thermoplastic. Although it is not always necessary to remove black thermoplastic if the marking is under 6mm, the use of black thermoplastic should only be a temporary measure because wear of the black material will eventually leave the white marking showing through.

2.3.2 Temporary Road Marking tape

When used for masking, the majority of the adhesive area is thermoplastic to which the temporary tape adheres relatively well. The black tape should be 50mm wider than the marking that it is covering. When removed, the tape generally leaves the road surface and the permanent marking in good condition.

2.3.3 Road marking paint

As a masking material, paint can be effective for masking either paint or thermoplastic markings and is fast to apply and is inexpensive, although a black grit must be surface applied to give the required anti-skid characteristic and a matt finish. It is particularly effective masking painted white lines. However, like thermoplastic, application of black paint for masking purposes is a short term solution only because the black paint will wear eventually to reveal white markings underneath.

Table 2: Road Marking Masking Material Options (View table)

2. Temporary Traffic Management Design and Specification

3. Road Surface Types

3.1 Description

In the last decade, thin surfacing systems, which are a diverse set of proprietary asphalt materials, have become the predominant surfacing option. For use on trunk and most county roads, a thin surfacing system must have a Roads and Bridges certificate under the Highway Authorities Product Approval Scheme (HAPAS) from the British Board of Agrément (BBA)1. For the purpose of this scheme, a thin surfacing system is defined as a proprietary bituminous product with suitable properties to provide a surface course that is laid at a nominal depth of less than 40 mm (BBA(2000)). An example of a document that gives further information on thin surfacings is Nicholls (2002).

Because the definition of thin surfacings is relatively wide, it is impossible to identify definitive properties for these systems. However, those currently on the market are designed with the preference for low-noise surfacings and have relatively open surfaces. As such, there are marked differences from the surfacings previously used for major roads which, in general, were of hot rolled asphalt with pre-coated chippings.

1 BBA-HAPAS certificates

BBA-HAPAS certificates can be downloaded from the relevant page in the BBA site on the web, www.bbacerts.co.uk/. The relevant page can be found by searching either for the name of the product or supplier or for thin surfacing to get a current list of the pages for all relevant certificates.

3.2 Advice on temporary markings for thin surfacings

When selecting the type of temporary marking to use on a particular scheme with newly laid asphalt, the properties of the asphalt layer should be taken in consideration. The acceptable options, based on a limited survey reported in Appendix A, are given in Table 3, but other factors, such as the type of site, may also have a significant effect but were not observed because of the similarity within the data reviewed.

The method for removing such markings should be considered before application is started.

Table 3: Acceptable options for temporary markings on newly laid surfacings
Layer thickness Max. nom. agg. size Binder type* Binder content Temporary Studs** Temporary Tape
< 35 mm 14 mm Unmodified > 6.0 % Suitable Suitable
6.0 % Suitable Possible
< 6.0 % Suitable Unsuitable
Modified > 4.9 % Suitable Suitable
4.9 % Suitable Possible
< 4.9 % Suitable Unsuitable
10 mm Unmodified > 5.4 % Suitable Suitable
5.4 % Suitable Possible
< 5.4 % Suitable Unsuitable
Modified > 3.5 % Suitable Suitable
3.5 % Suitable Possible
< 3.5 % Suitable Unsuitable
35 - 40 mm 14 mm Unmodified > 6.0 % Possible Suitable
6.0 % Possible Possible
< 6.0 % Possible Unsuitable
Modified > 4.9 % Possible Suitable
4.9 % Possible Possible
< 4.9 % Possible Unsuitable
10 mm Unmodified > 5.4 % Possible Suitable
5.4 % Possible Possible
< 5.4 % Possible Unsuitable
Modified > 3.5 % Possible Suitable
3.5 % Possible Possible
< 3.5 % Possible Unsuitable

* Definitions:

** Based on small 100mm x 50mm (4" x 2") studs in use at the time of writing.

3. Road Surface Types

4. Application and Removal

4.1 Application and Removal Issues

This section deals with the issues relating to the application and removal of temporary road marking materials. Section 4.2 gives more information on the methods available for removing the markings and a summary of removal methods is given in Table 4.

4.1.1 Hot Applied Thermoplastic

Hot applied thermoplastic adheres to the surface and, once applied, the bond cannot be penetrated by moisture. However, this bond cannot be created in the presence of moisture and debris and, therefore, the surface must be dried and cleaned prior to application. Nevertheless, thermoplastic can be applied in low temperatures and to all surfaces. It can be applied in a wider range of weather and temperature conditions compared with self adhesive studs and temporary tape.

Thermoplastic can be applied more thinly than in the permanent situation and this can lead to benefits in terms of quicker removal and possible less damage to the road surface.

4.1.2 Temporary Tape

Temporary tape adheres to the road surface by a waterproof seal with the carriageway. If this seal is penetrated by water, the adhesion fails. For good adhesion, the road surface must be dry, clean, free from salt, and the ambient temperature needs to be above 4oC. The surface is sprayed with a solvent-based primer which must then be left to dry. Tape is then applied onto the dry primer. Temporary tape does not perform well on open textured or rugous surfaces in wet conditions when water can flow through the surface and a pumping action causes the tape to lift.

At low temperatures, tape is less flexible and is less able to take the shape of the contours of the surface. The solvent based primers will not cure at low temperatures and cannot be applied in wet conditions.

There are situations when temporary tape can be removed easily and quickly from the road surface without leaving permanent residues, for example, when it is used as an edge line. However, if it has been constantly overrun for long periods, the polymer matrix can break up such that it can only be removed in small pieces. Under no circumstances should heat be employed to remove temporary tape as toxic fumes are given off.

4.1.3 Temporary Studs

Hot-melt temporary studs can be applied in all conditions, though this is dependent on the surface having been dried. Problems with adhesion can occur when steam pockets are created by the hot bitumen coming into contact with moisture that is resident in the voids of open textured surfaces.

Self adhesive temporary studs can be applied in most conditions, but the bitumen pad adheres less well at low temperatures. Drying of the surface prior to application is required. The stud adheres to the surface by the bitumen pad creating a waterproof seal with the surface. If this seal is penetrated by water the bond fails. Temporary self adhesive studs do not perform well on open textured or rugous surfaces. The application of a thixotropic glue prior to the installation of the self adhesive stud creates a waterproof seal between the bitumen pad and the surface and improves adhesion. This is particularly useful on thin surfaces.

Temporary studs can be removed from the road surface by sliding a shovel or "chipping bar" under the base of the stud. The most effective method of removal is by using a skid steer loader or tractor fitted with a bucket.

4.1.4 Road Marking Paint

Paint adheres to the surface by a chemical bond and its curing time is adversely affected by low ambient air temperatures, moisture and debris. The curing time prohibits its use during rain. Black paint requires a surface application of anti-skid material to aid abrasion and lessen highlight glare. White paint requires the application of glass beads to provide retroreflectivity.

Because paint is absorbed into the binder of the road, only the surface layer can be removed without damage to the surface. Masking with black paint is the only effective method. However, paint can be removed successfully from concrete carriageways because it is not absorbed.

4.2 Removal methods

Unless traffic is to be confined to a single lane delineated by closely spaced cones on each side (see Chapter 8, paragraph 3.1.3), where existing road markings conflict with temporary traffic management arrangements they must be removed or masked to avoid confusion in the interest of safety. Masking of the markings can be undertaken using temporary tape, thermoplastic or paint (see Section 2.3). The removal of road markings provides a permanent solution and avoids the possible failure of masking materials and consequent exposure of conflicting markings.

The main removal methods are as follows:

4.2.1 Hot Compressed Air (H.C.A.) Lance

This equipment works by using hot compressed air to vaporise the road marking. Because of the nature of the equipment used, it is regarded as a mechanical method of removal. The temperatures involved are likely to cause damage to the road surface and, for this reason, the equipment is inappropriate for use on thin surfaces. Noise, smoke and fumes are also important issues that need consideration. The H.C.A. lance operates at a relatively high noise level (120 dB(A)) and its appropriateness close to other site operations and urban areas must therefore be assessed. The vaporised thermoplastic can cause clouds of smoke which will affect drivers' visibility and, although not toxic, may be a health and safety issue.

4.2.2 Mechanical Scabbling

Mechanical scabbling grinds the marking from the surface, but total removal is not possible without damaging the surface. Small amounts of marking are left in the voids of the surface and this residue has to be masked or removed by other methods. The main use of mechanical scabbling is for removing the bulk of markings and the removal of raised ribline markings which are exceptionally thick. This method produces large amounts of debris that must be cleaned up quickly to avoid the thermoplastic particles re-adhering to the surface. The equipment is also relatively noisy and operates at 90 dB(A), but can peak to 104 dB(A).

4.2.3 Forced Air Abrasive (Shot Blasting)

Abrasive particles are projected by high pressure air at the road marking. The particles abrade the road marking from the road surface. This method leaves very little scarring because heat is not generated during the process but some polishing of the aggregate is likely. Total removal of road markings from porous/thin layer surfaces can only be undertaken with this process. The equipment is relatively noisy and operates at 105 dB(A). If this method is specified, the time factor must be considered because removal of road markings by shot blasting is very slow.

Consideration must be given to the environmental effects of the discarded abrasive material used during the removal process, especially in water courses. Captive shot blasting can be considered but the binder that is recycled with the abrasive material tends to clog the machinery.

4.2.4 Mechanical/hand chipping

This method is only suitable for removing temporary studs and tape.

4.2.5 New developments

New methods of removing markings are being developed. One that is commercially available is a method of forced air particle removal that employs dry ice as an abrasive particle. The dry ice vaporises during the removal process leaving very little debris. Another new system uses a heated mixture of sand and water applied at low pressure to remove markings. The developer claims that the removal process yields a relatively small amount of damp residue that can be swept up for later disposal.

Table 4: Options for the Removal of Road Markings
Method Minimising damage to: Low Noise/Fumes Speed of removal of:
HRA Surface Thin Surface Thermoplastic    Paint    Studs: Hot-melt, Self Adhesive Temporary Tape
Hot compressed air (HCA) lance *** * * *** * N/A N/A
Mechanical scabbling ****
Note A		 ***
Note A		 *** *****
Note A		 *
Note B		 N/A N/A
Forced air abrasive ****
Note C		 ****
Note C		 ** * * N/A N/A
Hand "chipping"/picking ***** ***** ***** * N/A ** **
Mechanical chipping **** **** **** N/A N/A **** ***


Key:
***** High/Good
**** Above average
*** Average
** Below average
* Low/Poor
Note A Removal of markings by mechanical scabbling can only be done to the point of damage of the surface. Total removal is not possible without some surface damage.
Note B Paint does not have any "bulk" to it so removal by mechanical scabbling cannot be undertaken.
Note C Polishing of the road surface occurs.
4. Application and Removal

5. Regulation and Approval Issues

5.1 Approved materials

5.1.1 Road markings

All road marking materials are subject to European Standards BS EN 1436; BS EN 1790 for preformed materials (e.g. tapes) and BS EN 1824 for road trials for materials from both standards. The physical properties of road marking materials are covered by BS EN 1871.

Approved materials are issued with a road trial test report to the appropriate standards by the testing organisation, like British Standards Institution (BSI), indicating which classes from the standard the material has achieved. The Manual of Contract Documents - Specification for Highway Works, Series 1200, has stipulated the minimum classes which will be required of any marking to be used on a trunk road.

Black masking materials, including temporary tape, thermoplastic and paint, are not included in the European Standards, but are covered by British Standard BS 7962.

It is essential that wear of the masking material should not expose the original white material below it.

5.1.2 Road studs

Road studs are subject to European Standards BS EN 1463 Parts 1 and 2. The Traffic Signs Regulations and General Directions 2002, including The Traffic Signs (Amendment) General Directions 2003, prescribe the minimum classes from those standards that must be achieved during trials of the studs to be used on the public highway. It would be unlawful to use a stud on the highway that was not certified to those minimum classes.

5.2 Stud option for standard road markings

Chapter 8 of the Traffic Signs Manual provides for the use of road studs at two metre spacing in place of lane markings in detail J2. Seven studs at one metre centres have been found to provide a better representation of the six metre marking being replaced and to retain a clearer appearance of a marking should any of the studs become dislodged. It is therefore recommended that one metre stud spacing should be used in situations where detail J2 is required.

5.3 Authorisation of markings

Only traffic signs, including road markings, which are prescribed in the Traffic Signs Regulations and General Directions or which have received special signs authorisation may be legally deployed on the public highway or other highway to which the public has access.

It is possible, in certain circumstances, to authorise the use of additional signs or markings by application in writing to the Department for Transport for England, and the appropriate organisation in Scotland, Wales and Northern Ireland. All applications are judged on their specific merits.

5. Regulation and Approval Issues

6. Summary

This report provides guidance for:

  1. designers in their choice and specification of temporary road markings, and
  2. practitioners on issues relating to the application, maintenance and removal of temporary road markings at road works.

The relative advantages and disadvantages of the three marking materials currently in use, and the temporary road stud alternative to markings, including their removal, are described and summarised in the form of tables. The type of road surface to which the marking is to be applied is important and, in particular, advice is included for temporary markings for thin surfacings.

Removing road markings presents particular problems, some of which are dependant on the type of road surface. There are advantages and disadvantages associated with each the methods currently available and these are summarised in the form of a table.

6. Summary

7. References

British Standards:

7. References

Appendix 1 - Advice on temporary markings for thin surfaces - background

Observations on the M6

In recent years, a series of sections of the M6 in Cheshire and Lancashire have been laid with a variety of thin surfacing systems that have behaved differently in terms of the embedment of temporary road studs and the adherence of road marking tape.

The systems have been identified and some simple characteristics of the mixtures used have been obtained. These characteristics are nominal maximum aggregate size, the nominal layer thickness, the target binder content and whether modified or unmodified binder was used. These characteristics, together with the observed behaviour of temporary road markings, are given in Table A1.

Properties of thin surfacing systems on M6
Junction Agg size (mm) Thickness (mm) Binder cont (%) Binder type Studs embed Tapes adhere
18-19, Holmes Chapel 14 30 6.0 Unmod No No
18-19, central 14 45 5.0 Mod Yes Yes
18-19, Knutsford 14 35 5.5 Mod Yes Yes
23, Haydock 14 35 6.0 Unmod No Yes
26-27, Gathurst * 14 30 4.9 Unmod No No
28-30, Leyland 14 35 6.0 Unmod No Yes
34, Lancaster 10 20 5.4 Mod No No
35, Carnforth 14 35 6.0 Unmod No Yes

* Studs fixed with thixotropic glue; only short lengths of transverse tape used, so adherence would have been more difficult than with longer lengths of longitudinal tape.

The characteristics of the thin surfacing systems are considered to be the type that can be readily attainable for any particular location.

Models to estimate performance

By comparing the characteristics, it is possible to produce models that estimate the performance of a thin surfacing system when temporary road markings are used. The embedment of studs is assumed to depend on the layer thickness (and hence the potential extent of any deformation) whilst the adherence of tapes is assumed to depend on the "stickiness" of the system, as indicated by the binder content and whether the binder is modified.

The data indicate a possible model for the embedment of temporary road studs could be that studs:

The data indicate that a possible model for the adhesion of road marking tape could be that tape:

where the adjusted binder content is the target binder content times cube root of the ratio of the maximum nominal aggregate size and 14 mm. This ratio is used to compensate for extra binder content needed to provide the same binder film thickness on finer aggregate skeletons.

A comparison of the observed and estimated behaviours is given in Table A2, with an overall accuracy of both models of 75 %. The limitations are the range of values where the estimated behaviour is uncertain.

Table A2: Comparison of observed and estimated behaviour on M6
  Observed Estimate Accuracy
Junction Studs embed Tapes adhere Studs embed Tapes adhere Studs embed Tapes adhere
18-19, Holmes Chapel No No No (?) 1.0 0.5
18-19, central Yes Yes Yes Yes 1.0 1.0
18-19, Knutsford Yes Yes (?) Yes 0.5 1.0
23, Haydock No Yes (?) (?) 0.5 0.5
26-27, Gathurst No No No No 1.0 1.0
28-30, Leyland No Yes (?) (?) 0.5 0.5
34, Lancaster No No No No 1.0 1.0
35, Carnforth No Yes (?) (?) 0.5 0.5
Total 6.0 6.0
Average 0.75 0.75

However, the models are only indicative because they are based on relatively few subjective observations. Furthermore, they relate specifically to freshly laid asphalt surfacings, and may not be applicable to surfacings that have been in service for some time.

Appendix 1 - Advice on temporary markings for thin surfaces - background