  Proton and alpha particle collisional transport coefficients (isotropization,
relative deceleration frequencies and heating rates) at 1 AU are quantified
using the WIND/SWE data. In agreement with previous studies the ion-ion Coulomb
collisions are generally important for slow solar wind streams and tend to
reduce the temperature anisotropies, the differential streaming and the
differences between proton and alpha particle temperatures. In slow solar wind
streams the Coulomb collisions between protons and alpha particles are
important for the overall proton energetics as well as for the relative
deceleration between the two species. It is also shown that ion temperature
anisotropies and differential streaming need to be generally taken into account
for evaluation of the collisional transport coefficients.
