Despite an increasing research emphasis on traffic prediction during the past twenty years, it would be incorrect to assume that the issue was totally ignored during earlier periods. It was, however, not until the 1920's that the growing number and use of private vehicles required noteworthy changes in highway infrastructure and a need to indulge in some limited prediction of increase in numbers with subsequent "planning" proposals and strategy. During the early 1950's it was estimated that at least 50 per cent of vehicles were owned or partly financed by firms or business interests. Legal powers to build motorways existed under the Special Roads Act of 1949 but it was not until December 1958 that the first section of motorway was opened. Typical is the work of Farrell, who paid particular attention to economic explanation for changes in demand for cars.