A fully dynamical and finite-lempel'dture study of the electron momenhum relaxation rate and mean free path in a coupled system of electrons and bulk LO phonons in a quantum wire structure is presented. Electmn-electron and electron-phonon interactions are eeated on an &at footing within the leading-order perturbation theoq and random-phase approximation. It is demonstrated that coupled-mode effects drastically change the tramport propties of the system at low temperatures. In panicular. the 'plasmon-like' and 'LO-phonon-like' excitations yield comparable rates which, as a consequence of the singular nahlre of the ID density of states, can be large at the threshold. This is in contrast to room temperature results where oniy the LO-phonon mode conuibutes significantly to the rate.