Road Note 39 is a guide for the design of surface dressing for roads throughout the United Kingdom (it is NOT prepared as, nor should it be used as, a specification). This Sixth Edition of the Road Note is produced by a Panel representing all sides of the industry, with the Chairman and Secretariat provided by the Infrastructure Division of TRL Limited. The following extract emphasises the importance of the Road Note: “Surface dressing can be used successfully on all types of roads, from the country lane that carries only an occasional vehicle to trunk roads and motorways carrying thousands of vehicles a day. It provides a simple but cost-effective form of maintenance. Unfortunately, the attention paid to design, control, supervision and aftercare is frequently less with surface dressing than with more expensive forms of construction. Lack of attention to detail shortens the useful life of a surface dressing; the benefits of adequate control, particularly in the period when traffic is first allowed on the new surface dressing, cannot be emphasised too strongly.” The principal differences from the Fifth edition are: CEN standards (European standards have been introduced for aggregates and bitumen and are being introduced for surface dressings and so there are a lot of changes to the standards that need to be referenced); Nomenclature for aggregates (European standards for aggregate have introduced a nomenclature for aggregates of d/D, where d and D are the minimum and maximum sizes, so that the use of a/b for multiple system surface dressings would now become more complex and has been discontinued); Nomenclature for emulsions (the European standard for bitumen emulsions has replaced the K1 70 classification by several, more specific classifications); Cut-back binders (cut-back binders are no longer generally available from binder suppliers in the UK and so have been removed, leaving all binders to be one of the varieties of bitumen emulsion); Spread rates for proprietary polymer-modified binders (polymer-modified bitumen emulsions now represent a major part of the market so the rates quoted in the Road Note with an assumed binder (solids) content of 67 % can be adjusted by multiplying by 67 over the proportion declared for bitumen emulsions with a different proportion); Traffic categories (the weight of passenger vehicles has increased, particularly with the use of people carriers and off-road vehicles becoming more widespread so that the proportion of vehicles over 1.5 t is increasing and the number of roads with very low flows of medium and heavy vehicles is reducing); Simplicity (as far as practicable, the method has been simplified without changing the basic methodology and, in particular, the use of categories for binder spread rates has been discontinued); and Electronic documentation (where documents are available on the web, the web address is given that can be used. (Author/publisher)
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