Remarks on the Present System of Road Making / With Observations, Deduced from Practice and Experience, With a View to a Revision of the Existing Laws, and the Introduction of Improvement in the Method of Making, Repairing, and Preserving Roads, and Defending the Road Funds from Misapplication. Seventh Edition, Carefully Revised, With an Appendix, and Report from the Select Committee of the House of Commons, June 1823, with Extracts from the Evidence

by John Loudon McAdam

TO THE RIGHT HONOURABLE
THE PRESIDENT,
AND
THE BOARD OF AGRICULTURE.

Having communicated to your Honourable Board, some observations on making and repairing roads, in February, 1819, I beg leave to add the following, which have arisen from increased experience on the subject, and also from a desire of calling your attention to the effects of the late severe winter on the roads of the country, and the confirmation afforded to the opinions I have endeavoured to introduce on the construction of roads.

During the late winter, and particularly in the month of January, 1820, when the frost was succeeded by a sudden thaw, accompanied by the melting of snow, the roads of the kingdom broke up in a very alarming manner, and to an extent that created great loss and inconvenience by the interruption of communication, and the delay of the mails, and also occasioned a very heavy extra expenditure by the Post-office.

The obvious cause of this defect of the roads, was the admission of water from the loose and unskilful method of their construction. Previous to the severe frost, the roads were filled with water, which had penetrated through the ill-prepared and unskilfully laid materials: this caused an immediate expansion of the whole mass during the frost, and upon a sudden thaw, the roads became quite loose, and the wheels of carriages penetrated to the original soil, which was also saturated with water, from the open state of the road. By this means, many roads became altogether impassable, while the whole were rendered deep and inconvenient to be travelled upon.

In particular, it was observed, that all the roads of which chalk was a component part, became, generally, impassable; and even, that the roads made over chalk soils gave way in most places. This evidently proceeded from the absorbent quality of chalk, which renders it so tenacious of water, that I consider its use to be one of the most dangerous errors in road making. I was induced on former occasions to recommend particular care in making roads over chalk soils, and to advise a discontinuance of the practice of mixing chalk, clay, or any other matter that holds water, with the materials of a road. The experience of last winter has confirmed this opinion, and has shewn the ruinous effects of the former method.

Of all the roads which have been thoroughly re-made, according to the directions which I had the honour to submit to your Honourable Board last spring, not one has given way, nor has any delay taken place through the severity of the late season.

As every winter has, in some degree, presented such inconveniences, and as it has been observed that very severe winters occur in England every six or seven years, it is of great consequence to consider of the means of constructing the roads of the kingdom in such a manner as shall prevent their being in future affected by any change of weather or season.

The roads can never be rendered thus perfectly secure, until the following principles be fully understood, admitted, and acted upon: namely, that it is the native soil which really supports the weight of traffic: that while it is preserved in a dry state, it will carry any weight without sinking, and that it does in fact carry the road and the carriages also; that this native soil must previously be made quite dry, and a covering impenetrable to rain, must then be placed over it, to preserve it in that dry state; that the thickness of a road should only be regulated by the quantity of material necessary to form such impervious covering, and never by any reference to its own power of carrying weight.

The erroneous opinion so long acted upon, and so tenaciously adhered to, that by placing a large quantity of stone under the roads, a remedy will be found for the sinking into wet clay, or other soft soils, or in other words, that a road may be made sufficiently strong, artificially, to carry heavy carriages, though the sub-soil be in a wet state, and by such means to avert the inconveniences of the natural soil receiving water from rain, or other causes, has produced most of the defects of the roads of Great Britain.

At one time I had formed the opinion that this practice was only a useless expence, but experience has convinced me that it is likewise positively injurious.