The name of Telford is associated with a pitched foundation, which he did not always use, but which closely resembled that which had been long in use in France, and the name of McAdam often characterizes roads on which all his precepts are disregarded. Both insisted on thorough drainage and on the use of carefully prepared materials, and adopted a uniform cross section of moderate curvature instead of the exaggerated roundness given before ; but, while Telford paid particular attention to a founda tion for the broken stone, McAdam disregarded it, contending that the subsoil, however bad, would carry any weight if made dry by drainage and kept dry by an impervious covering. McAdam was engaged more with the repair of old roads than with the construction of new ones, and, though it is not possible to agree with all his doctrines, the improvement which he effected in road management and maintenance was great and lasting. When McAdam died in 1836 the turnpike system had attained its widest extension, no less than I,Ioo trusts being then in existence. The dawn of the railway era brought disaster to the turnpike trusts, and roads suffered a long period of neglect at the hands of the parochial authorities who were mainly responsible for their upkeep.
The Public Health Acts of 1848 and 1875 and the Local Government Acts of 1888 and 1894 set up, stage by stage, the system of road-administration which now prevails in Great Britain,—the responsibility for main roads resting generally upon county councils, while less important roads are in the hands of urban district councils and rural district councils. The Develop ment and Road Improvement Funds Act (1909) established the road board, now merged in the Ministry of Transport, which makes grants from the Government's road fund towards the expenses incurred by the highway authorities just named.
Incidentally, an impervious surface will prevent the deteriora tion of the foundation and will enable the camber or crown of the carriage way to be reduced, thereby adding to the safety and convenience of drivers. Cambers of 1 in and even steeper, used to be common. In modern practice this has been reduced to I in 48. In the design of new highways sufficient land is fre quently acquired to enable all pipes, mains and conduits to be laid under the verges, shoulders or margins, so that the carriage way itself may not be subject to future disturbance. Dimensions
of Too ft. or ft. between fences are becoming common in Eng land, while in the United States even more generous figures are adopted. In England it has become common to adopt a To ft. factor for the width of carriageways, e.g., for three streams of traffic a 3o-ft. carriageway would be provided, for four streams 40 ft.
The wide road allows space for tree planting and keeps noise and vibration at a tolerable distance from the householder's windows. Spacious footways and verges on each side of a car riageway extend the motorist's view as he rounds a curve and promote the safety of vehicles entering from side roads. Drivers gain a wider range of vision on each side and secure an extra fraction of a second for deliberation before venturing into the main stream of traffic.
Sharp bends and abrupt changes of direction are now dis countenanced in favour of easy curves of long radius. Where, owing to the configuration of the ground, curves of less radius than i,000 ft. are unavoidable the outer edge of the carriageway is super-elevated or "banked," following the invariable practice 'The British refer to cambers in this way ; in the United States they are referred to as in. to I ft. or 1 in. to i ft. (ED. E.B.) of railway engineers. The width of the carriageway should be increased at such points. Steep gradients which disfigure the rigidly straight Roman roads are avoided by moulding the line to the contours of the hillside. In laying out new arterial roads of which upwards of 200 miles have been built in the neighbour hood of London since the year 1920, it has almost invariably been found possible to limit the gradients to 1 in 30. Gradients of excessive flatness (less than 1 in 300) are to be avoided, owing to the difficulty of effectively draining the surface.
The elimination of level crossings over railways is an important item in the programme of modern road-improvements, and the time is fast approaching when, in the interest of public safety bridges may have to be provided at points where important high ways cross one another.