We present a comprehensive experimental study of the tunneling and tra
nsport characteristics of split-gate ''leaky'' one-dimensional (1D) el
ectron waveguides implemented in AlxGa1-xAs/GaAs heterostructures. In
a leaky electron waveguide, electrons can tunnel out of the 1D channel
through a thin side wall barrier into an adjacent 2D electron bath. A
sharp peak and valley structure is observed in the 1D-to-2D tunneling
current as the carrier concentration is modulated in the 1D waveguide
through the field-effect action of the split gates. A semiclassical m
odel confirms that the tunneling features originate from the 1D subban
ds in the channel.