A gravity equation for commuting with an application to estimating regional border effects in Belgium

This article derives a gravity equation for commuting and uses it to identify the effect of regional borders on commuting. We build on the seminal trade paper by Anderson and Van Wincoop (2003, Gravity with gravitas: a solution to the border puzzle. <it>The American Economic Review</it>, 93: 170–192) and highlight some interesting similarities between our model and Wilson’s doubly constrained gravity equation [Wilson, A. (2010) Entropy in urban and regional modelling: retrospect and prospect. <it>Geographical analysis</it>, 42: 364–394], a workhorse model from spatial interaction theory. The model is estimated by applying a negative binomial regression method on Belgian inter-municipal commuting data. We show that regional borders exert a sizeable residual deterrent effect on commuting, a finding with obvious implications for regional labour market integration. This border effect differs significantly between regions and depends on the direction in which the border is crossed.