A Travel-to-work Area (TTWA) theoretically represents a self-contained labour market area in which all commuting occurs within the boundary of that area. It has been re-defined once a decade when analyses on commuting patterns drawn from the UK Censuses were completed. In December 2015, the Office of National Statistics (ONS) published TTWAs based on the 2011 Census results.
TTWAs are used primarily to aid understanding of labour markets across the UK. However, residential location and commuting patterns can also contribute to understanding local housing markets. The conventional assumption is that local labour markets are spatial proxies for housing markets. Indeed, housing professionals have been employing TTWAs in this way in their strategic plans.
One of the issues in using existing TTWA s in this way is that they do not allow for overlap. Consider a household with two earners, one of whom is commuting within the TTWA while the other is commuting to a business hub outside their TTWA. For example, Cambridge TTWA has now expanded as far south as Hertford and Harlow - settlements containing many London commuters.
Taking Cambridge as our example we attempt in this paper to experimentally identify commuting areas for Cambridge that lie within the boundaries of other employment hubs, such as Ely. In this way we can start to address the reality that TTWAs, certainly in terms of local housing markets, are not discrete - they overlap.