  We have studied the isoscalar giant quadruple resonance (ISGQR) and the
isovector giant dipole resonance (IVGDR) in $^{208}$Pb based on an improved
isospin-dependent Boltzmann-Uehling-Uhlenbeck transport approach using an
improved isospin- and momentum-dependent interaction. With the isoscalar
nucleon effective mass and the nucleon-nucleon cross section which reproduces
respectively the excitation energy and the width of the ISGQR strength
function, the slope parameter of the symmetry energy and the neutron-proton
effective mass splitting are constrained respectively within $36<L<62$ MeV and
$0.08\delta<(m_{n0}^*-m_{p0}^*)/m<0.42\delta$, by comparing the resulting
centroid energy of the IVGDR and the electric dipole polarizability with the
experimental data. It is found that nucleon-nucleon collisions have
considerable effects on the resulting electric dipole polarizability, which
needs to be measured more accurately in order to pin down isovector nuclear
interactions.
