  The ultrarelativistic limit of twodimensional dilaton gravity is presented
and its associated (anti-)selfdual energy momentum tensor is derived. It is
localized on a null line, although the line element remains twice
differentiable. Relations to the Aichelburg-Sexl spacetime and constant dilaton
vacua are pointed out. Geodesics are found to be smooth for minimally coupled
test particles but non-smooth -- with a finite jump in the acceleration -- for
test particles coupled non-minimally to the dilaton. Quantization on boosted
backgrounds is discussed; no anomalous trace of the energy momentum tensor
arises and the 1-loop flux component can be adjusted to be equal to the
classical flux of the shock wave.
