  A combination of the inclusive diffractive cross section measurements made by
the H1 and ZEUS Collaborations at HERA is presented. The analysis uses samples
of diffractive deep inelastic ep scattering data at a centre-of-mass energy
sqrt(s) = 318 GeV where leading protons are detected by dedicated
spectrometers. Correlations of systematic uncertainties are taken into account,
resulting in an improved precision of the cross section measurement which
reaches 6% for the most precise points. The combined data cover the range 2.5 <
Q2 < 200 GeV2 in photon virtuality, 0.00035 < xIP < 0.09 in proton fractional
momentum loss, 0.09 < |t| < 0.55 GeV2 in squared four-momentum transfer at the
proton vertex and 0.0018 < beta < 0.816 in beta = x/xIP, where x is the Bjorken
scaling variable.
