Source: adapted from E.J. Taaffe, H.L. Gauthier and M.E. O’Kelly (1995) Geography of Transportation, Second Edition, Upper Saddle River, NJ: Prentice Hall, p. 223.
Technological innovations had an impact on the friction of distance, which is reflected in the reduction of the beta exponent used on spatial interaction models. Lower beta values imply a reduction of the friction of distance. The introduction of jet planes had significant impacts on the reduction of the beta exponent in the 1960s. Improved speed and capacities made air transportation more affordable and air travel (interactions) increased substantially. Therefore, keeping all other factors constant, the same city pairs generate more air traffic flows simply because it is more affordable to fly.