Highways Agency Press Release
There has been a development since I wrote the above introduction, the Highways Agency have issued a news item in response to the concerns about early life skid resistance of stone mastic asphalt. 
I suggest you use the link I have provided and form your own opinion as to whether it satisfies your concerns.
The item, it appears, is to particularly address the worries of motor cycle riders.
I find the content very interesting, but then I know more than most on the subject and I personally cannot agree with all the statements made, others may, but it is a well crafted piece of work for the purpose intended.
But I do think that the suggestion that there is no SMA on Highways Agency roads is playing with words, and may not be well received by some suppliers who include the term "SMA" in marketing some of their proprietary bituminous surfacing mixtures. 
I also think it is worth noting that the item is written/prepared by "DeHavilland Information Services" a company that provides "news information service for latest current affairs and political news", and not an Engineer, or Engineering Consultancy, an Engineering Journal, or even a spokesman for the Quarry Products Association.
Perhaps we are getting closer to the reason for the introduction of the exclusive use of proprietary Thin Surfacings on motorways and trunk roads in England than you think.

But to try and provide some clarity in what has become an extremely confusing situation, 

• There is no one single stone mastic asphalt
• There is no one single hot rolled asphalt
• There is no one single close graded bitumen macadam
• There is no one single porous asphalt
• There is no one single open graded bitumen macadam
• Etc. for all forms of road surfacing

All these bituminous mixtures are the result of designing and blending aggregates, from sources of aggregate (quarries) all over the UK, with differing amounts of bitumen.
The aggregates will have differing physical properties, and will be proportioned to different designs and mixed in different types of batching plants, with different bitumen viscosities supplied from several major suppliers. 
The supplied bitumens are likely to be sourced from differing crude oil stocks and may be modified with various synthetic or natural modifiers. The bitumen must be stored and used within certain time and temperature constraints to ensure the bitumens do not degrade before incorporation in any bituminous mixture, or indeed after mixing whilst in storage bins.
So, what am I saying is that there is the potential for hundreds, possibly thousands, of combinations to produce the sum of the various bituminous mixtures I have named above, and that includes SMA, generic or proprietary.
The properties of the bituminous mixture will depend upon the quality, blending and mixing of its components, not on the name it may carry.
Just as a rose will smell as sweet if you call it a turnip, you will not get the same fragrance from a turnip if you call it a rose.
You probably know what I am going to say next, but I will say it anyway, you need a qualified and experienced Materials Engineer / Road Pavement Engineer to help you decide on the appropriate bituminous mixture for particular surfacing requirements, not a "news information service for latest current affairs and political news". 
How many hours/days/years have they spent by the side of a paving machine, in a materials laboratory or in a dusty, wind swept, quarry yard.

If you wish to know more about proprietary Thin Surfacings, Stone Mastic Asphalt and bituminous road surfacing mixtures in general there are plenty of pages on this website and links to other websites to provide you with more information than you really want to be bothered with, and you should also try a little Googling using "sma early life skid resistance" as your keywords.

One website that is to be highly recommended to increase your knowledge on the topic of bituminous mixtures for roads is that of R.J.Maxwell & Son Ltd., it has an excellent "education" section.

What is a Thin Surfacing
Design Manual for Roads and Bridges – Volume 7 – Pavement Design and Maintenance – 
HD 37/99 : Bituminous Surfacing Materials and Techniques - Chapter 6 : Thin Wearing Course Systems
“6.1 Thin wearing course systems, or thin surfacings as they are more commonly described, are proprietary systems in which a hot bituminous bound mixture is machine-laid with a controlled screed paver onto a bond or tack coat to form, after compaction and cooling, a textured wearing course generally less than 40mm. in thickness.”

It would be sensible to read all of HD 37/99 if you want a better understanding of bituminous surfacing materials and techniques, after all the Department for Transport have gone to the trouble of publishing it, and you can download it free of charge from the “web”. 
It is also stated in Clause 942 of Volume 1 of the Specification for Highway Works (SHW) that Thin Surface Course Systems shall have a British Board of Agrément HAPAS (Highways Authority Product Approval Scheme) Roads and Bridges Certificate applicable to the combination(s) of traffic level and site classification given in Appendix 7/1 of your contract document, in accordance with the Specification for Highway Works.
There are other conditions included in Clause 942 appropriate to the use of a bituminous mixture that has been produced under a Thin Surface Course System that has a HAPAS certificate, e.g. texture depth.

I personally do not regard an actual 40mm. thickness of surface course as “thin” but a standard thickness that will provide durability and contribute load spreading strength to the road pavement.

It is also necessary to make reference to the “Guidelines Document for the Assessment and 
Certification of Thin Surfacing Systems for Highways”, which should be obtainable from the British Board of Agrément
It is the criteria in this document that determines whether a Thin Surfacing System achieves certification.
The British Board of Agrément introduced this document in 1997, in draft form. 
The draft copy I have is dated January 2000 and I believe it is still in draft form at this time, although it may be a more recent draft.
With regard to skidding resistance of a Thin Surfacing, a pre-wetted skid resistance test is not a mandatory test (Table 1) for HAPAS approval, what is required is the appropriate combination of polished stone value (PSV) of the aggregate, and texture depth.
After removal of surface bitumen this combination should/will achieve the skid resistance appropriate to the site conditions.
A pre-wetted skid resistance test (SCRIM) can be specified as an optional test (Table 2), but required performance levels are not specified in the draft Guidelines Document that was still current on the 26/2/2004.

It has to be noted that HAPAS approval is not an approval of an individual product, it is an approval of a system, and that system will comprise a series of mixtures with varying blends of binder, filler, fibres, coarse and fine aggregate dependent upon site specific requirements.
So, it might be quite a complicated, and expensive, process to obtain individual pre-wetted SCRIM values for each individual bituminous mixture covered by a particular Thin Surfacing System.

What is a Stone Mastic Asphalt
There are a number of ways of defining SMA, the description I think most appropriate is to be found in :
TRL Report 314 – Road trials of Stone Mastic Asphalt and other thin surfacings – by J. C. Nicholls
Chapter 2 – Para 2.1 : Stone Mastic Asphalt 

The description is quite comprehensive and I would suggest that you read it, along with the rest of this excellent report. 
But to quote just a small section, which basically summarises what an SMA should be, “The single sized nature of the aggregate skeleton leaves a relatively high void content between the aggregate particles which is partly filled with a binder rich mastic. As such, the aggregate grading is similar to that of a porous asphalt, but with the voids filled with mastic.” 

I would also suggest you read,
TRL Project Report 65 – Evaluation of stone mastic asphalt (SMA) : A high stability wearing course material. This report will give you a background on the introduction of SMA into the UK from Germany, and an insight into its development, production and use in Germany.

In order that an SMA can be used on motorways and trunk roads in England it must be produced to a “system” that has HAPAS certification and then it can be regarded as a proprietary Thin Surfacing.
( This is where I believe "people" have been playing with words over whether SMA has or has not been used on Highways Agency supervised road networks. )
Generic SMA is a “Not permitted” option for use on motorways and trunk roads in England, see :
Design Manual for Roads and Bridges – Volume 7 – Pavement Design and Maintenance – 
HD 36/99 : Surfacing Materials for New and Maintenance Construction – Chapter 2 : Surfacing Options – Table 2.2E (England) : Permitted Pavement Surfacing Materials for New and Maintenance Construction

I am aware that work on early life skid resistance of SMA by TRL started early in 2002 soon after the reported problems in Derbyshire. Considering the potential seriousness of this issue you would have thought that at least an interim publication of achieved data might have been appropriate, but I believe this data is still unpublished.

Tyre / Road Noise
Following on from the topic above, we have to remember that one of the prime reasons for the introduction of proprietary Thin Surfacings was to reduce tyre generated road noise. 
It is important to remember that the tyre generates the noise (especially wide, high pressure, super singles) not the road surface, but the nature of the road surface plays a significant role in how much noise the tyre will generate.
So you may like to purchase a recently published report from the Transport Research Laboratory (TRL).
It is :
Published Project Report PPR023 : Comparison of Tyre/Road Noise for a Range of Surfaces

I believe it costs just £15:00, from the TRL Publications Unit, and I regard it as an absolute bargain.
The work was undertaken by the TRL, under a commission from a local authority, using the newly developed TRITON, a purpose built vehicle containing an advanced system for monitoring the noise emitted from tyres as they run over a road surface.
I believe this is the first published work of the use of TRITON, although I am aware that it has done work for other agencies/organisations that is not yet published.
All the road surface types, of which there is a wide range, including hot rolled asphalt, stone mastic asphalt and surface dressing are generic bituminous mixtures.
It is my opinion that TRITON is an excellent addition to the current range of road survey equipment that is being developed. 
It would just be nice to see its wider use and the publication of the results. It would then be possible to make better judgments on the choice of road surfacing materials, in relation to  road noise generation , based on evidence.  
I think you will be surprised by the results.
But what it does clearly indicate, as I have described above,  you cannot make simple statements that one broad material classification is "noisy" or "quiet" just because of the general description/name that the bituminous mixture/process carries.

And, Another One Bites the Dust
It is with real sadness that I have recently heard of the ensuing demise of a large "testing laboratory" facility, of possibly the largest highways maintenance consultancy in the UK. 
This former local authority soils and materials laboratory has tremendous respect in the industry, and is one of the few that has UKAS accreditation for a full range of materials and soils testing procedures.
I hope this report is incorrect, or that the decision can be reconsidered, or influenced by the wider industry, who, in my opinion, have no idea how much they need facilities such as this in the increasingly commercial highways maintenance industry.

Warning
Reading this newsletter will not make you an expert. I am not an expert, I have some knowledge on the subject of highways materials because of the years I have  spent in the profession. I wish I knew a lot more than I do, but it is unlikely my knowledge will increase much more in the current situation the industry has got itself into, i.e. everything being commercially sensitive and hence secret.
There are few well equipped independent local authority Soils and Materials Laboratories left, if any, that will openly exchange the type of information that needs to be shared.
I can remember when it was expected that at least 1% of the total highway budget would be spent on various types of sampling and testing, does not sound a lot does it, but not any more.
Perhaps this months effort will at least stop people making rash statements, and will at the same time allow them to ask more relevant, and searching, questions of individual problems on particular sectors of the highway network.
I hope the considerable amount of work I have put into this newsletter will indicate that selecting, specifying, designing, producing, and storing bituminous surfacing mixtures is not a simple process, and I have not mentioned transporting, laying and compaction.
All organisations responsible for looking after highway networks, should not be tarred with the same brush, (no pun intended), some do quite a good job considering the "pressure" they work under.
Finally, if I can make a plea for some sanity in the industry. Stop setting up groups with no road engineering knowledge to organise "us". If "we" are unable to perform our function, i.e. maintain highway networks, give us early retirement deals and let us go, and let the organisers do the work. "They" are obviously far better at highways maintenance than we are, because "they" are the ones telling us what to do, I think it is fortunate that some of us are not programmed to blindly follow.

Motto of the Month

"There are none so blind as those that will not see"