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The Idiots' Guide to Highways Maintenance
Copyright 2000/14, C.J.Summers

SKID RESISTANCE AND HIGH FRICTION SURFACING

CONTENTS  
INTRODUCTION TO FACTORS AFFECTING ROAD SURFACE SKID RESISTANCE ROAD SURFACE TEXTURE (MACRO-TEXTURE)
SOME WIDELY USED TERMINOLOGY AND ITS MEANING SITES REQUIRING A PARTICULARLY HIGH RESISTANCE TO SKIDDING
MEASURING ROAD SURFACE SKID RESISTANCE METHODS OF ACHIEVING / RESTORING A GOOD SKID RESISTANCE SURFACE
Portable Skid Resistance Tester (Also known as the "Pendulum Tester") HIGHWAY AUTHORITY PRODUCT APPROVAL SCHEME ( H.A.P.A.S.)
SCRIM, Sideways Force Coefficient Routine Investigation Machine INITIAL ROAD SURFACE TEXTURE DEPTH - CLAUSE 921 SERIES 900 SHW VOLUME 1 - AUG.  2008
Griptester PERSONNEL COMMENT
Road, Pavement Friction Tester (PFT) WARNING ! An important change has taken place to this item, it needs reading.
VERY USEFUL REFERENCE SOURCES  
   
The following items are extremely important and need to be read ! ! !  
ONGOING DEVELOPMENTS RELATING TO POLISHED STONE VALUE (PSV) AND TEXTURE DEPTH REQUIREMENTS OF THIN SURFACE COURSE SYSTEMS - (Summer 2012 Newsletter)
NEW INTERIM ADVICE NOTES (IAN's 154/12, 155/12, 156/12) RELATING TO SKID RESISTANCE VALUES AND POLISHED STONE VALUES OF NEW HIGHWAY SURFACING - (Autumn 2012 Newsletter)
NEW -  INTERIM ADVICE NOTE IAN 49/13 - Use of Warning Signs for New Asphalt Road Surfaces  Further reading relating to the introduction of IAN 49/13 is on the page, Spring Newsletter 2013
NEW - TRL Published Project Report - PPR564 The skid resistance behaviour of thin surface course systems  - Topic 1 Final Report - 29/11/2012
          (This report being the basis to the above documents and topics and therefore needs study.)

INTRODUCTION TO FACTORS AFFECTING ROAD SURFACE SKID RESISTANCE

The types of skid resistance, and factors affecting skid resistance that this guide will give information on are those applicable to road surfaces normally encountered in highway maintenance and road construction.

It is important to understand that all road surface skid resistance monitoring relates to wet/damp road surfaces, and the testing takes place after the road surface has been pre-wetted.

This is because road surfaces will exhibit least friction/skid resistance when they are wet.

Although testing of dry road surfaces does take place from time to time by individual testing laboratories, it does not form any part of the routine skid resistance monitoring that takes place on the UK road network.

It can be assumed that, in dry conditions all clean surfaced roads have a high skidding resistance 
This is documented in, 

DfT. Design Manual for Roads and Bridges, Vol.7 : Design Manual HD 36/99 : Surfacing Materials for New and Maintenance Construction : Section 5-Surfacing and Surfacing Materials : Chapter 3-Texture and Aggregate Properties

I have deliberately left what may be considered superseded items on this page to demonstrate how initial surface texture depth requirements of highway surfaces have been decreased over a number of years.
So when KSI's (killed and seriously injured) figures are being compared over the years, they can be compared in conjunction with the texture depths of the respective accident sites.

In the future we may even want to consider the specified Polished Stone Value (PSV) of the aggregate in the surface course bituminous mixture when examining accident figures over time.

SOME WIDELY USED TERMINOLOGY AND ITS MEANING

Polished Stone Value, PSV

This is a value of an individual aggregate, found by subjecting the aggregate to a standard polishing process and then testing the aggregate with the Portable Skid Resistance Tester.
The testing procedure and description of the process is set out in,
B.S. 812:Part 114.

PSV IS A VALUE APPLICABLE TO A PARTICULAR AGGREGATE, NOT THE ROAD SURFACE.

Aggregate that has a PSV value over 60 is regarded as a High Skid Resistant Aggregate.
The higher the PSV figure the greater resistance the aggregate has to polishing, and the greater the ability the aggregate has to retain its own natural very fine texture, (roughness).

THE PSV PROPERTY OF AN AGGREGATE IS OFTEN REFERRED TO AS MICRO TEXTURE, i.e. the retained microscopic texture inherent in a particular aggregate, however long it is polished the aggregate will never truly become smooth/polished.

Skid Resistance Value, SRV

This is the value obtained from the actual road surface, measured using the Portable Skid Resistance Tester.
The resistance to skidding of a road surface, i.e. its' SRV, is dependent on the PSV of the aggregate in the wearing course material AND the large texture, (roughness), of the surface of the wearing course material.

THE TEXTURE / ROUGHNESS OF THE ROAD SURFACE IS OFTEN REFERRED TO AS MACRO TEXTURE

MEASURING ROAD SURFACE SKID RESISTANCE

Portable Skid Resistance Tester (Also known as the "Pendulum Tester")

the portable skid resistance tester, often referred to as the "pendulum tester" because of its action This is the piece of test equipment for measuring PSV's and SRV's.
The nickname originates from the pendulum action of the rubber slider that contacts the surface to be tested.
This equipment is hand operated for individual results and is not suitable for testing long lengths of road.
Instructions for use and information on the portable skid resistance tester can be found in,
ROAD NOTE 27 from the Transport and Research Laboratory.

I personally still very much like this piece of equipment, even if you can only use it for relatively small lengths of road that need testing.
The sheer compactness of the instrument allows you to quickly respond to a situation, or piece of work, with minimum cost of traffic management, often no cost if the testing is done at the same time as the work.

The apparatus is quite basic, quite robust, and does not easily go out of calibration if treated with the respect a precision instrument should be given.
The process is quite simple, the pendulum is released from the horizontal position by a quick release button, it swings down with uniform force each time, and the rubber slider at the bottom of the pendulum contacts the road surface for a fixed length that you have previously set by highering or lowering the height of the pivot of the pendulum.
The degree to which the pendulum will rise up the the calibration on the left-hand side of the image will be dependant on the friction / resistance the rubber slider meets on the road surface. 
The more friction / resistance the less the pendulum will rise and the higher the Skid Resistance Value (SRV) of the road surface.
adjusting the length of contact that the rubber slider will contact the road surface when it "swings", part of a before and after testing procedure when retexturing Swinging with the pendulum is a pointer that cannot be seen on the photograph, and as the pendulum falls back the pointer will be left in place indicating the SRV.
The other good, practical, thing about using this apparatus is that when you are on your knees operating the pendulum tester you get a very good look at the road surface and the aggregate that constitutes the surface, and this can be very revealing.
It has to be said operating the pendulum tester is beneath the dignity of many highway engineers, even in their training days, that is why some of us actually know more about road surfaces than those that just sit in offices.

See :-
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


This standard describes a method for determining the slip/skid resistance of a surface using a device which remains stationary at the test location. The slip/skid resistance is measured by means of a pendulum incorporating a rubber "slider" which is dragged across the road surface as the pendulum swings.
The "swing" of the pendulum will be retarded to a greater or lesser extent depending upon the friction characteristics of the road surface.
The pendulum swings with a pointer that remains against a scale of SRV's when the pendulum swings back, and a value is able to be recorded.


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 the PORTABLE SKID RESISTANCE TESTER, press ------>
HERE,  (This is a particularly informative site offering useful information on skid resistance testing.)


SCRIM, Sideways Force Coefficient Routine Investigation Machine

SCRIM showing the position of the test wheel housingTest wheel housing opened showing test wheel being calibrated This machine is a lorry chassis with a large water holding tank similar in size to a "gully emptyer", but it has mounted in its mid-section left side wheel track, a test wheel that is set at 20 to forward travel.
This creates a pressure on the wheel related to the skid resistance of the road surface.
This pressure can be measured and is processed to give figures, SFC's, that represent the road surface skid resistance.
The SCRIM normally travels at 50 km/h and so is capable of surveying many kilometres of road in a day.
This speed has led to the use of SCRIM to conduct large surveys of road network to ensure adequate skid resistance of the road surface.


SFC, Sideways Force Coefficient


The SFC is the value of the skidding resistance of a road surface obtained using the SCRIM, and be careful with the terminology SRV and SFC, because SFC's are not the same as SRV's, they are almost the same but not quite, but for practical purposes they may be considered so.

See :-
BS 7941-1 : 1999 : Methods for measuring the skid resistance of pavement surfaces
Part 1 : Side-way force coefficient routine investigation machine


This standard describes a method for determining the wet-road skid resistance of a surface using the sideway-force coefficient routine investigation machine (SCRIM). 
The method provides a measure of the wet-road skid resistance properties of a bound surface by measurement of the sideway-force coefficient at a controlled speed. 
The method has been developed for use on roads but is also applicable to other paved areas such as airport runways.


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 SCRIM, press ------------------------------------------------------------>
HERE


Griptester

underside of Giiptester road surface friction tester  This is an excellent small three wheeled device with the "normal" axle being connected to the recording wheel by a pair of gears which causes a braking effect on the axle of the third wheel which can be measured as a "Grip Number".
If you are able to obtain a copy of,
TRL Project Report RR/H/58/93
this will explain and compare the apparatus to a SCRIM.

This equipment can be used pushed by hand on a pre-wetted road surface for small area surveys.

As the Griptester has developed in to a more precise piece of equipment it has been taken up by many organisations as their standard means of assessing roads and runways for skid resistance, and a number of user groups are well established to further develop and support its use.  

Griptester attached to towing vehicle

Large plastic water tank with 
metering pump connected to laptop

Griptester in use
Griptester attached to towing vehicle accurately metered pumped water supply via laptop to adjust for road speed Griptester in use performing road surface friction survey

See :-
BS 7941-2 : 2000 : Surface friction of pavements - 
Part 2 : Test method for measurement of surface skid resistance using the GripTester braked wheel fixed slip device


This standard describes a method for determining the skid resistance of a surface using the GripTester continuous reading braked wheel fixed slip device. 
The method is for measurement of skid resistance along a continuous surface on external paved surfaces, or indoors. 
Test speeds can vary from 5km/h to 130km/h depending upon application. The measured values can be affected by the test speed.


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 GRIPTESTER, press -------------------------------------------->
HERE


Road, Pavement Friction Tester (PFT)

Pavement friction tester (PFT) in operationThis device differs from the already described methods by actually employing the "locked" wheel principle and measuring the friction between the fully braked wheel and the road surface.
The TRL now owns a PFT, and pictures and description of the apparatus and how it is used can be found in :- 

TRL Report 367 : High and low speed skidding resistance : the influence of texture depth

Pavement friction tester showing water feed to test wheelThe PFT is the standard apparatus for testing the friction of road surfaces in the USA, it is a towed trailer with both wheels having hydraulically applied disk brakes which are activated by compressed air. 
It uses the locked-wheel principle in accordance with ASTM Standard E274 (1990)

I believe the machine owned by the TRL has only the left side wheel fitted with the braking system on this machine.
 

 


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 the PAVEMENT FRICTION TESTER, press --------------->
HERE


VERY USEFUL REFERENCE SOURCES

DfT. Design Manual for Roads and Bridges, Vol.7 : Design Manual HD 28/04 : Skidding Resistance
DfT. Interim Advice Note (IAN) 98/07 - Guidance for HA Service Providers on Implementing the 
Skid Resistance Policy HD 28/04
DfT. Design Manual for Roads and Bridges, Vol.7 : Design Manual HD 36/99 : Surfacing Materials for New and Maintenance Construction


County Surveyors Society Reports ENG/7-94, and ENG/3-95 :
The Achievement of Skidding Characteristics for Road Pavements,
Volume 1:An Overview,
and
Volume 2:PSV values for Aggregate in UK Roads


TRRL Report 510 : A guide to levels of skidding resistance for roads
TRRL Report 466 : Aggregates for resin bound skid resistant surfacings

TRRL Report 296 : The relationship between surface texture of roads and accidents             
TRL Report 367 : High and low speed skidding resistance : the influence of texture depth

NEW - I can confirm that it is now possible to download copies of TRRL Report 296 and TRL Report 367 from the TRL website free of charge, both are extremely informative and comprehensive reports on the subjects of road surface friction, skid resistance and texture depth and their inter reaction, I recommend that you read them both.
( I suggest that you take advantage of the current excellent facility of downloading TRL Reports, free of charge, as soon as you can, I am fairly confident that this recently introduced facility will be withdrawn under pressure from commercial interests, but I hope that I am wrong.
And a tip, it seems you have more success in finding the reports that you want if you search on keywords in the title rather than the report number.)


The book "ROAD AGGREGATES AND SKIDDING" by Roger Hosking, available from H.M.S.O.
and
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
BS 7941-1 : 1999 : Methods for measuring the skid resistance of pavement surfaces - Part 1 : Side-way force coefficient routine investigation machine
BS 7941-2 : 2000 : Surface friction of pavements - Part 2 : Test method for measurement of surface skid resistance using the GripTester braked wheel fixed slip device


For an excellent report from the Highways Agency's website, covering most aspects of road surface skid resistance, written by someone who obviously knows their subject for those who need to know, look under the sub-heading, "Composition and condition of the road surfacing", after pressing  HERE 


ROAD SURFACE TEXTURE (MACRO-TEXTURE)

Texture is measured by the Sand Patch Method on small areas, i.e. areas of new bituminous surfacing surfacing prior to allowing it to be trafficked.
The method is fully documented in B.S. 598:Part 105, however this method has already, or is soon to be superseded by a very similar method but using a standard sized glass bead in place of sand.
However for practical purposes either method will give you a fairly accurate assessment of road surface texture.
 
The principle is fairly obvious the greater the texture the more the sand will be taken up by it and the smaller the circle that can be achieved from the standard quantity of sand. 
There is a simple formula in the British Standard that allows you to determine an average texture depth from the diameter of the sand circle.

But there is an area of controversy regarding the measurement of texture in positively textured road surfaces, e.g. hot rolled asphalt and precoats, and surface dressing,
and
negatively textured road surfaces such as porous asphalt, and Thin Surfacings that are porous in nature.

It is suggested that sand or glass beads will fall into the voided structure of a porous material and so produce a result for surface texture that is not related to the texture that is able to be exploited by the contact area of the vehicle tyre.
I will leave you to read the literature that is available on this subject and to ponder on whether this is a reasonable hypothesis.

sand patch test equipment, high texture hot rolled asphalt and precoats, ten years old newly laid hot rolled asphalt and precoats, low texture due to precoats being "lost" into the asphalt the sand patch test consists of ten individual tests diagonally across a fifty metre length of carriageway


Large areas/lengths of road that need assessing for texture depth are tested by the,
High Speed Road Monitor or the High Speed Texture Meter.

These devices employ lasers pointing at the road surface to measure texture, and the measurement recorded in this way is known as Sensor Measured Texture Depth, (SMTD).

Be careful SMTD results cannot be compared directly with the texture depth figures obtained by Sand Circle texture depth testing.

E.g. 1.5mm texture depth by sand circle = 1.1mm texture depth by SMTD, and is THE SAME ACTUAL TEXTURE DEPTH, with regard to skid resistance requirements

SITES REQUIRING A PARTICULARLY HIGH RESISTANCE TO SKIDDING

Although all roads require good skid resistance there are some situations that will require a higher level of skid resistance than others:-

1) Approaches to Pelican Crossings, and some junctions, islands and bends

These sites need the highest possible skid resistance available.
This will usually mean an anti-skid process using a resin as the binder and Calcined Bauxite chippings of approx. 2mm. to 3mm. size as the high PSV aggregate.
This can be achieved in two ways :-

a)
by applying the resin, (an epoxy resin for trunk roads), to the road surface and applying Calcined Bauxite chippings onto the binder to give complete shoulder to shoulder cover for maximum texture.
For large areas this process is normally machine applied but resins capable of being mixed and applied by hand are now available.

b)
by applying the resin and calcined bauxite together operation in a hot applied operation. The thermoplastic resin and calcined bauxite aggregate is premixed in poly bags and then heated in a large "boiler" to the required temperature.
The molten material is screeded on to the road surface using a 300mm. wide bottomless "shoe" at right angles to the direction of traffic, in lane widths.

These processes gives good MACRO TEXTURE, and the PSV of Calcined Bauxite is about as high as you can get, approximately.
75 PSV for Guyanan (grey),
70 PSV for Chinese (buff coloured).
These processes should give SRV's or SFC's in the range 70 to 80 depending on the process, and the quality of the workmanship.

2) Trunk Roads

The D.O.T. have a requirement in their specification that road surfaces shall have a minimum texture depth, (MACRO TEXTURE), of 1.5mm., (by "Sand Patch" not by SMTD).
This
was normally achieved by having a wearing course of 30%/14mm HRA and applying a layer of 20mm. precoated chippings which are rolled into the asphalt while it is still hot.
The PSV of the precoat will be a minimum of 55 for straight sections of road with no junctions, bends or other hazards.
It is more usual to specify a minimum PSV of 60 for all average sites, and where there are tight bends or hazardous junctions a minimum PSV of 65 is required.
(See D.O.T. Standard HD 28/94 for further information.)
The above surface treatments will give SRV's and SFC's of 55 to 65.

The use of Hot Rolled Asphalt Wearing Course with Precoats is not now permitted as a wearing course option on motorways and trunk roads in England.
All wearing course now has to be proprietary "Thin Surfacing".


3) Principal Roads and other highly trafficked roads

This group of roads can still use the Hot Rolled Asphalt wearing course and Precoats option.

METHODS OF ACHIEVING / RESTORING A GOOD SKID RESISTANCE SURFACE

1) Resin / Calcined Bauxite processes as described, HERE

2) Specify bituminous wearing course material that will have a high SRV, e.g. hot rolled asphalt wearing course with 20mm. precoted chippings of a high PSV applied at the correct rate to achieve a high texture, see HERE

3) Surface Dressing with a high PSV chipping is an excellent process for restoring skid resistance to the surfaces of all classes of road, on sections that are suitable for the treatment, shown HERE

4) Re-texturing of a sound road surface by a mechanical abrading process, (best for surfaces with a high aggregate content), or a high pressure water method, (best for binder rich surfaces), as described HERE

A compilation of individual items of information related to Skid Resistance can be accessed by pressing HERE

(NEW ) 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 excellent information on the skid resistance of roads and runways, that is able to be downloaded in .pdf format,  press, 
HERE

HIGHWAY AUTHORITY PRODUCT APPROVAL SCHEME ( HAPAS)

This is a recently introduced organisation to "approve" new products for use in highway maintenance and construction, so that individual authorities do not need to undertake their own trials.
It has been set up by the Highways Agency (HA), CSS (formerly the County Surveyors Society) and the British Board of Agrement (BBA), with the involvement of bodies representing private industry.

I am concerned about products and processes that gain approval / certification at national level with little true participation of local authorities or local contractors.

The development of HAPAS is administered by the BBA, closely advised by the Highways Technical Advisory Committee (HiTAC), certificates of approval are issued by the BBA acting on recommendations from HiTAC.

Specialist groups, with a strong industry representation, are created for each product type.

Products and processes are put forward for consideration by the group who will report back its findings to HiTAC, who will in its turn make recommendations to the BBA as to whether the product / process should receive HAPAS approval.

Full details of the particular schemes and the criteria for assessment are available from the British Board of Agrement.

British Board of Agrement ------------------------------------------------------------------------------------------> www.bbacerts.co.uk

A list of High Friction Surfacing products and installers that have HAPAS approval / certification will be found on the above site.
Copies of certificates of some of the products that have received approval can be downloaded in "pdf" format from this same site.

THIN SURFACINGS have now become products/systems that are able to receive HAPAS approval, replacing Highways Agency approval, but the mechanism by which THIN SURFACINGS gain approval
has been the cause for some debate, as "systems" of THIN SURFACINGS are receiving approval rather than individual products.
Copies of certificates of some of the products/systems that have received approval can be downloaded in "pdf" format from the BBA site.

For more information on Highways Authority Product Approval Scheme, press ---------> HERE

For more information on proprietary Thin Surfacings, press ---------------------------------------> HERE

INITIAL ROAD SURFACE TEXTURE DEPTH - CLAUSE 921 SERIES 900 SHW VOLUME 1 AUGUST 2008

This is a completely revised 900 Series of the Specification,
i.e. Manual of Contract Documents for Highway Works (MCHW) - Volume 1 - Specification for Highway Works (SHW) - Series 900 - Road Pavements -Bituminous Bound Materials.

It has been introduced to coincide with the publication of the new European Standards for bituminous mixtures, 
BS EN 13108 family of standards for Bituminous Mixtures
. from the 1st.of January 2008. 
The specification has also introduced a number of important changes other than those related to the specifying of bituminous mixtures to BS EN 13108.

One of the most important of these changes, which in my opinion is not a "minor revision", is the reduction in initial texture depth of "thin surface course systems" (TSCS) on high speed roads, to not less than 1.3mm., and to not less than 1.0mm. on low speed roads and roundabouts on low speed roads.
I urge you to obtain a copy of the 900 Series Road Pavements - Bituminous Bound Materials, it can be download from,  www.standardsforhighways.co.uk
and study Clause 921-Surface Macrotexture of Bituminous Surface Courses.

In previous editions of the "900 Series" , e.g., as recently as November 2004, the figure quoted was the single figure of 1.5mm. for "high speed roads" but with no clear indication of what a high speed road was so the default was 1.5mm, so in my opinion the changes are significant and you must be aware of them.
In the current Clause 921 there is a table containing the minimum texture depth requirements for defined surfacing materials, speeds of roads and locations, etc..

To obtain further information on these extremely important changes please read the recent newsletters,  Summer 2008 and Autumn 2008

NEW - TRL Published Project Report - PPR564 The skid resistance behaviour of thin surface course systems  - Topic 1 Final Report - 29/11/2012

This Published Report has been prepared for the Highways Agency, the Mineral Products Association and the Refined Bitumen Association

I include here the summary provided by TRL on their website, and in doing so acknowledge their copyright.

"Proprietary thin surface course systems have been successfully used on UK trunk roads for over 10 years, providing quiet surfaces while maintaining good friction when the road is wet.
However, the process of approving them focussed on compliance with existing specifications that had been derived from the properties of traditional materials such as hot rolled asphalt (HRA) and surface dressings, prevalent at the time.
Collaborative research sponsored by Highways Agency (HA), the Mineral Products Association (MPA), the Refined Bitumen Association (RBA) sought to optimise requirements for thin surface course systems to maintain safety standards, further improve durability and make more efficient use of resources.
Skid resistance and texture depth were monitored on a range of trial sites, constructed specifically for the project, and in-depth laboratory studies were developed to help give a better understanding of the effects observed in the field.
The results from the project have made it possible to make recommendations for changes to the requirements for thin surface course systems regarding the polish resistance of aggregates and texture depth with reference to the size of coarse aggregate in use."


This is an important document and I believe that it must be studied by practising highway engineers, the only comment I will add that it does state in the introduction, "The programme has not included sites in higher stress locations.", what this exactly means I am not sure but the text goes on to indicate a continuing programme of research.

Authors P G Roe and A Dunford      (Pages 62)
Date 29/11/2012                    Reference PPR564                           ISBN x ISSN 0968-4093
 

PERSONNEL COMMENT
I cannot understand the discrimination in the recent changes to Clause 921 against positive textured hot rolled asphalt and precoats, and surface dressing (both of which are not even permitted options on motorways and trunk roads at this time) and thin surface course systems with regard to initial texture depth.

I can to some extent understand the logic of lowering of initial texture
requirements on lower speed roads.
But not on sites such as roundabouts, or approaches to roundabouts, even if we assume that everybody will be obeying the speed limit on a particular length of highway.

In my opinion these changes are removing the "safety factor" that engineers have always tried to build into their highway surfacing designs.

If somebody is saying that anybody who drives too fast is not entitled to be as safe as the Engineer can reasonably make him, perhaps they would like to stand up and say so, in order that Engineers who have to follow these "rules" are not deemed responsible in a court.
Remember it is not always the person who is driving too fast that gets hurt in an accident.

I believe that we have to live in a real world, where drivers very often do drive too fast, and I believe this change will decrease the safety of our motorway and trunk road network, and particularly if coupled with the voiced reduction in the polished stone value (PSV) of the aggregate in Thin Surface Course Systems.
(See the Autumn 2008 Newsletter)
In my opinion these changes in the construction and maintenance of the highway network are not something that the highways construction and maintenance industry can be proud of. 

Finally, I would remind Engineers who have the responsibility of maintaining local authority highway networks that following the direction indicated by the Highways Agency is not compulsory, although most do follow their guidelines, as usually they can be regarded as excellent.
It will be some time before it will be generally known whether these changes will impact on the actual skid resistance values of road surfaces obtained from surveys, I believe they will.
Over recent years I can only speculate that some of the changes have been brought about by commercial/political influence, with some of the changes being fairly quickly dropped when they did not work, at great cost I may add.
This time the cost may not be counted in money.
Please leave the engineering to the Engineers who work with, and on, real roads, and consult them for their opinion before making major changes.
It could save those in charge a great deal of embarrassment, as I think "some" are beginning to fall into the "the Kings's new clothes" syndrome, for those of you who can remember Danny Kaye on "Kiddies' Favourites" on a Saturday morning.
Where the purveyors of the King's new "suit" can be likened to clever "marketing" men playing on the ignorance and insecurity of the King and those who surrounded him, with his "court" wishing to retain their good positions and so just acquiescing to the "message" from the top. 
I am too old to be the little boy who cries, "the King is naked".

But I can recommend that you read some of the "older" TRL Reports relating to highway skid resistance, two of which I refer to above, and which I know can now be downloaded from the TRL website, read the item above
Very Useful Reference sources.


WARNING !

Interim Advice Note IAN 49/13 - Use of Warning Signs for New Asphalt Road Surfaces

The items below are now superseded by
Interim Advice Note IAN 49/13 - Use of Warning Signs for New Asphalt Road Surfaces, however I am leaving the original text as a "history" of how the issue of "early life skid resistance" has been dealt with in the past.
It is important that you obtain a copy of IAN 49/13 as soon as possible, as this IAN is already current.
Further discussion of this topic can be found on the Spring 2013 Newsletter.

The introduction of IAN 49/13 is largely based on the work covered in,
TRL Published Project Report - PPR564 The skid resistance behaviour of thin surface course systems - Topic 1 Final Report - 29/11/2012, details of which are published above.
 


Sites that have developed a low skid resistance, for whatever reason, must be picked up and dealt with quickly by a suitable remedial treatment.
If this cannot be done "Slippery Road" sign boards should be prominently displayed.
Claims against Highway Authorities have been upheld in court where the authority has been thought to have been negligent in respect of road surface skid resistance, failing to investigate a possible danger, or failing to inform of a possible risk after investigation.

You may wish to obtain and study :-

Interim Advice Note IAN 50/03 : Investigation of sites identified from skid resistance measurements
Volume 7 - Pavement Design and Maintenance Manual - Section 3 : Pavement Maintenance Assessment

and,
Interim Advice Note IAN 49/03 : Use of warning signs for new asphalt road surfaces
Volume 7 - Pavement Design and Maintenance Manual - Section 5 : Surfacing and surfacing materials

The above now being largely replaced by, 
DfT. Design Manual for Roads and Bridges, Vol. 7 : Design Manual HD 28/04 : Skidding Resistance
and the associated
DfT. Interim Advice Note (IAN) 98/07 - Guidance for HA Service Providers on Implementing the 
Skid Resistance Policy HD 28/04


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