§ Mr. Marples
Roads are designed for three lanes of traffic where traffic studies show that this layout will be adequate and economic for many years to come. Normally this means that the traffic is likely to be too heavy to permit a free flow on a two-lane road but still insufficient to justify dual carriageways.
On all-purpose trunk roads three-lane single carriageways have been or are being provided on approximately one-eighth of the total mileage of major schemes (including both widenings and new lengths of road) completed since 1955 or now under construction. If motorways are included in the total the proportion is approximately one-thirteenth. I regret that comparable figures for classified roads are not readily available.