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The Idiots' Guide to Highways Maintenance
Copyright © 2000/14, C.J.Summers
WHITE LINES AND ROAD MARKINGS (BS 3262)
|INTRODUCTION TO SPECIFYING THERMOPLASTIC ROAD MARKINGS||SAMPLING, TESTING, SUPERVISION|
SETTING OUT OF LINE SYSTEMS,
AND THE MATERIALS USED
PERFORMANCE TESTING OR RECIPE
OF THE THERMOPLASTIC ROAD MARKINGS
|BS EN SPECIFICATIONS RELATED TO ROAD MARKINGS||
THE RETROMETER AND
OF THE ROAD MARKING
|GENERAL INFORMATION REGARDING ROAD MARKING||SAFETY THAT IS PROVIDED BY ROAD MARKINGS|
|QUALITY ASSURANCE SCHEMES|
I am fully aware that road markings are now specified to a range of newly introduced BS EN Standards which I will list elsewhere, BUT, because of the somewhat haphazard way the new BS EN documents have become available there are many road marking contracts still in force that relate to BS 3262.
And it will do you no harm at all to know what BS 3262 offered in its thoroughness and simplicity before it is thrown away.
( The last time I browsed the BSI website you could in fact still buy copies of these documents, and I can still recommend them for their excellent content even if you can no longer use them as a specifying standard. )
But if you really want to know ( before you finish reading this page ) what the new specifications are you will find reference to them in the page that refers to all the new road marking specifications and related reports and guidance documents, by pressing ---------------- > HERE
The need for road markings of all types is becoming increasingly important in controlling the position of moving traffic into orderly lanes and in showing the road user where he can and cannot be on the highway.
White lines are still the major part of road markings and make an important contribution to road safety, particularly during the hours of darkness, and in this context the ability of the line to reflect light from the vehicle back to the driver, i.e. retro-reflectivity, has become increasingly important and is now specified.
This is not to forget the very important properties of line durability, luminance ("brightness") and skid resistance.
SETTING OUT OF LINE SYSTEMS, AND THE MATERIALS USED
Specifications for Road Marking Layouts
If you need to know information about types of lines, positioning of lines, dimensions of lines, etc., there are three publications you need to be aware of.
The most useful is :-
TRAFFIC SIGNS MANUAL 5, ROAD MARKINGS, 1985.
But you may also need to refer to :-
TRAFFIC SIGNS MANUAL 3, REGULATORY SIGNS, 1986.
The statutory document is :-
THE TRAFFIC SIGNS REGULATIONS AND GENERAL DIRECTIONS, 2002.
The above document can be accessed (on a good day) by pressing HERE, courtesy of HMSO, it includes drawings and dimensions relating to road marking.
LOCAL TRANSPORT NOTE 2/87, (SIGNS FOR CYCLE FACILITIES), is necessary for cycle signs.
Specifications for Road Marking Materials
The thermoplastic line itself, i.e. the nature of the materials it is made from, how you expect it to perform, and how you apply it to roads surfaces is comprehensively covered by :-
BS 3262 : Hot-applied thermoplastic road markings,
It was in three parts :-
Part 1 : Specification for constituent materials and mixtures.
Part 2 : Specification for road performance.
Part 3 : Specification for application of material to road surfaces.
Other relevant specifications relating to road markings are :-
BS 6088 : Specification for solid glass beads for use with road marking compounds and for other industrial use
BS 6044 : Specification for pavement marking paints
D.fT. Standard TD 26/04 - Inspection and maintenance of road markings and road studs on motorways and all-purpose trunk roads
Specifies minimum requirements for line quality for trunk road work, including a 12 month minimum retro-reflectivity figure of 100 mcd/lux/sq.m., although this figure is not necessarily ensured, as I read the new document.
SPECIFICATIONS RELATED TO ROAD MARKINGS
You now need to know all about the new BS EN Specifications for road marking, some of you may even be using the new specifications now.
You will find the new standards listed in the "database" on road marking, but at this point in time I am not going to say anything about them on this page, as I have provided a page specifically relating to the new standards.
However It is my belief that you will not be wasting your time in learning about BS 3262 before moving on to the new system, and it is possible to tweak the new specification to contain elements of BS 3262 if you know where to look in the new standards.
The Process of "Road-marking" Described
Briefly the thermoplastic material is a mixture of a light coloured silica sand, (a bulking agent), a white pigment, (to make it look white), a resin binder, (to hold it all together), and some glass beads, (to make the lines shine in the dark by reflecting the headlight beam back to the driver).
The property of the night-time visibility of a line is known as its retro-reflectivity, or sometimes specific luminance.
Glass beads are also added to the still molten thermoplastic line surface to increase the initial retro-reflectivity of the line.
When the line surface becomes worn, the retro-reflectivity of the line will then depend on the glass beads incorporated in the thermoplastic material becoming exposed with wear.
This continuing ability of the line to reflect light to the motorist will be enhanced by the quantity and quality of the glass beads in the thermoplastic, and the whiteness of the line matrix.
BS 3262 will tell you all you need to know about the above items, a recent amendment has included a retro-reflectivity requirement at a fairly low level.
The thermoplastic material must contain the specified amount of resin binder that has not been overheated for its long term durability.
(And, just for clarification, all "thermoplastic" means is that when the material is hot it is plastic, i.e. able to be poured, and when it is cold it is solid.)
Also the quality of workmanship cannot be underestimated in producing road markings of high quality and good durability, and it is an unfortunate fact that you tend not to get good workmanship without good supervision.
"Class A" Material
The term "Class A" material was explained in BS 3262:Part 2:Clause 3.
But briefly what it means is, a particular sample of white line material complying with BS 3262:Part 1 was laid in accordance with BS 3262:Part 3, on a known site, (the A1 at St. Neotts), and after 2 years its properties remained in accordance with the requirements of BS 3262:Part 2 when tested as prescribed in the various appendices of
BS 3262:Part 2.
This is taken to mean a particular formulation of thermoplastic, when laid correctly, is still capable of meeting the specified requirements after two years in the traffic conditions of the test site.
The theory being, it is a test of the quality of the material.
The approval in reality is for that material used on that site, at that time.
But, can you be sure you are getting the same material quality on general white lining work years after the formulation was approved, and even if you are receiving the same formulation, without the same standard of workmanship in laying the markings the life of the lines could be considerably reduced.
It is a bit like Q.A. but that is another story.
It is necessary to sample and test the thermoplastic on a regular basis, how regular will depend on the results you obtain, it is not difficult to obtain a samples of road marking material and results can be interesting.
It is usually not necessary to be over enthusiastic on sampling, but by random sampling when convenient you are able to build up a picture of types and qualities of material used by contractors.
It may also be possible to establish a "fingerprint" of different types of material so that in cases of dispute we may be able to confirm or not, as the case may be, the identity of a white line material.
This particularly being the case with proprietary materials that are claimed to have enhanced properties.
When sampling, the actual information about the thermoplastic material used needs to be noted, i.e we need product information taken from the bagged material on site, this is usually printed on the side of the bag.
It will then be possible to relate results obtained to types of material, this will become increasingly important as different manufacturers supply new materials.
The results to date prove that a specification figure of 250 mcd/lux/sq.m. for retro-reflectivity at 28 days is not unreasonable, and quite able to be obtained with materials supplied and laid to the British Standard.
A six month figure of 200 mcd/lux/sq.m. also seems to be a figure that can be readily achieved with British Standard materials, and most importantly, good quality workmanship in laying.
Some authorities already require much higher retro-reflectivity requirements than the above in their contract documents, and conversely some do not have a separate requirement for night time visibility but defer to the 100 mcd/lux/sq. m. now included in the British Standard.
Several of the large manufacturers of road marking thermoplastic are marketing materials guaranteeing figures of 200, and even 300 at six months, or when the initial surface has been abraded to expose the matrix of the material, providing the materials have been laid in accordance with BS 3262.
Even with these materials, good early retro-reflectivity is dependent on correct application of good quality glass beads to the still molten surface of the white line.
All thermoplastic materials, (and this includes bituminous materials), have a maximum temperature to which they should be heated.
If you heat the material over this temperature it will be damaged to a greater or lesser degree depending on the temperature it is heated to, and how long it is kept at that temperature.
White line thermoplastic if over heated will become brittle and be more prone to wear and disintegration, as well as discolouring.
With bituminous materials there are appropriate specified temperatures included in the British Standards.
However with white line thermoplastic the relevant maximum temperature will be that specified by the manufacturer of the material, this is usually printed on the bag.
Taking temperatures of material when it is convenient is not a bad idea, and this has become remarkably easy with the introduction of "laser" thermometers. "Laser" thermometers are now inexpensive and easily carried in your pocket.
It is another factor that helps us build up information on the performance of contractor and demonstrates to him that the purchasing authority is very much interested in quality.
This is the type of testing favoured by some authorities and will be the major part of the new BS EN documents.
Performance testing allows the contractor to use materials and processes that are not necessarily to the British Standard providing the finished lines/markings meet performance criteria laid down in the contract specification.
The methods for testing the performance of the laid road markings are usually those procedures laid down in,
Part 2 of BS 3262, (so you may find the British Standard is still heavily quoted in some performance specifications).
To be able to police a regime of performance testing it is necessary have sufficient staff and suitable equipment to undertake the testing of lines on site, often in traffic sensitive areas.
This can occur the expense of traffic control if you wish to test in all situations, and the cost of the traffic control often exceeds the cost of the testing.
Whenever possible it is best to test road marking performance at the same time as the markings are applied to take advantage of the existing traffic control.
This has the added bonus that if the markings fail the contractor is on site to rectify them.
If the markings fail to meet performance standards at a later time of testing they will still have to be removed and replaced, or over laid if dimensions permit.
This type of testing follows the principle that if you use materials to a particular specification, (recipe), and you lay them in a specified manner then the finished product will perform as required.
This was the former BS 3262 way of doing things, and you still have the performance requirements should you need them, so the superseded BS 3262 was very much a "belt and braces" situation.
Retro-reflectivity of a line marking is a factor which can only be assessed by performance testing.
But if a correctly formulated line has had applied the correct amount of "in specification" glass beads in the manner specified, it is most likely it will achieve the retro-reflectivity requirement.
I have to declare I have a preference for the "recipe" way of working.
I like the idea of getting things set up at the time of doing the work to do it correctly, it saves a lot of hassle later on when performance testing shows line marking properties to be inadequate.
Unfortunately it requires a level of supervision difficult to provide, and that is if the engineer knows where the contractors are working at any particular time, ( contractors tend to move around a lot ).
I try to
refer to as few commercial sites as possible in compiling my
site, but when a site offers particularly useful information
about a subject I make an exception.
For further information on road marking materials, press --------------------------------------------> HERE
A suggestion that could be considered is a submitted line laid at the beginning of a contract in a suitable location, e.g. a depot yard or an absolutely specific highway location.
The laying of this line could be supervised closely and all tests carried out upon it to verify the contractors ability to be able to lay line markings to the required standard.
If the contractor is unable to demonstrate, at this stage, his ability to lay correct markings it is unlikely he will be able to lay markings to specification when on site, but in reality the contractor will lay good markings to the required standard.
If as the contract progresses the standard of the markings degenerates the client is able to point out the quality of line required by reference to the submitted lines, use of submitted samples in highway construction is regular practice.
THE RETROMETER AND
RETRO-REFLECTIVITY TESTING, (Night-time
Visibility of Road Markings)
The Retrometer is a piece of equipment that is able to measure the ability of the surface of a white line to reflect light from a cars headlights back to the driver, it is relatively small and hand portable, the readings obtained are millicandelas per lux per square metre, (mcd/lux/sq.m.).
|Retro-reflectivity results are the average
of five individual readings taken approx. 20 cms. apart on a
Three results will be obtained for a particular locality, and these three results averaged to give an overall figure for the site, the road marking will be tested for retro-reflectivity in a dry condition after removing loose dirt and dust, (although local agreements have been arrived at to wash and dry the line in a prescribed manner before testing occurs).
Modern versions of the Retrometer are becoming more robust in construction, but it is a precision instrument that does need to be treated with care in use and transportation, and it also needs to be regularly calibrated to a known reference standard.
As with all laboratory testing, results will depend upon the competence of the laboratory and their technicians, and most importantly the actual sites chosen and their representative nature, whatever figure you decide upon for retro-reflectivity requirement it is a minimum figure, all results should be above this figure.
I try to
refer to as few commercial sites as possible in compiling my
site, but when a site offers particularly useful information
about a subject I make an exception.
For more information on retrometers and retroreflectivity, press ----------------------------------------------------> HERE
You can now find many excellent video clips of road marking application and testing on YouTube, but it is like any other "searching" you need to enter appropriate key words or you may get some weird "finds".
Road markings are used in many ways to convey a great deal of information to the road user to control traffic movements and provide safe road conditions, and in daylight or under street lighting the markings are relatively easy to see.
However, in the dark, the retro-reflectivity of the line becomes a prime safety factor, allowing the vehicle driver to see the line of the road in front of him, as well as the information contained within the road markings.
It is the desire to increase night time road safety that increased specification for minimum retro-reflectivity of white lines has been introduced.
The testing of white lines for retro-reflectivity using the retrometer has been introduced to ensure the white lines produced by contractors meet the specification requirements.
It is also a fact that some road situations have large areas of laid road marking materials, these areas need to have a Skid Resistance Value (SRV) in keeping with the site situation, and this is not always easily obtained when you are also seeking to achieve a high retro-reflectivity quality in the line, a SRV of 55 is an often specified value.
The SRV of the marking is determined using the Portable Skid Resistance Tester in accordance with,
TRL Road Note 27,
BS EN 13036-4 : 2003 : Road and airfield surface characteristics - Test methods -
Part 4 : Method for measurement of slip/skid resistance of a surface - The pendulum test
Do not assume because a contractor has Q.A. Certification this is a guarantee that the work he performs will automatically comply with the specification.
The contractor has been certified that at the time of his assessment he complied with the procedures of his quality plan, you do not know what is in his quality plan, so you do not know what procedures he is certified as complying with.
Without knowledge of what is in the Quality Manual of a company, the words "Certified to BS 5750 or ISO 9000", (or whatever version we are up to now) does not mean a lot.
But, it is the contractor / supplier who should be taking full advantage of quality assurance in ensuring his procedures bring about a quality product in an efficient manner, and should anything go wrong there is traceability of the method and product to establish what went wrong, and so know how to put it right.
It is not for the client / purchaser to be impressed by "bits of paper", he should be impressed by the quality of the work produced by the contractor.
There is no substitute for adequate knowledgeable supervision if an authority wants good work and value for money, and of course knowing where your road marking contractor is at any particular point in time.
you have read this far because you are interested in obtaining good
quality road markings, may I suggest you take some time to study the
excellently crafted road marking specification, and guidance document,
produced by the "Irish".
I do not think you will be disappointed by its clarity and common sense, but you will still need the staff, and the materials laboratory backup to ensure that the contractor complies with the specification.
The specification can be downloaded by pressing, HERE
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