  The nature of a metal--insulator transition tuned by external gates in
quantum Hall (QH) systems with point constrictions at integer bulk filling, as
reported in recent experiments of Roddaro et al. [1], is addressed. We are
particularly concerned here with the insulating behavior--the phenomena of
backscattering enhancement induced at high gate voltages. Electrostatics
calculations for QH systems with split gates performed here show that
observations are not a consequence of interedge interactions near the point
contact. We attribute the phenomena of backscattering enhancement to a
splitting of the integer edge into conducting and insulating stripes, which
enable the occurrence of the more relevant backscattering processes of
fractionally charged quasiparticles at the point contact. For the values of the
parameters used in the experiments we find that the conducting channels are
widely separated by the insulating stripes and that their presence alters
significantly the low-energy dynamics of the edges. Interchannel impurity
scattering does not influence strongly the tunneling exponents as they are
found to be irrelevant processes at low energies. Exponents of backscattering
at the point contact are unaffected by interchannel Coulomb interactions since
all channels have same chirality of propagation.
