The 1930s saw several major depression relief projects built by manual labour, including the first inter-city divided highway in North America along the Middle Road, which would become the Queen Elizabeth Way in 1939. In 1937, the DHO merged with the Department of Northern Development, extending the highway network into the Canadian Shield. Significant traffic engineering and surveying through the war years, during which construction came to a near standstill, led to the planning and initial construction of controlled-access highways. The 400-series highways were built beginning in the late 1940s and numbered in 1952.