  Besides the traditional data collection by stationary detectors, recent
advances in wireless and sensor technologies have promoted new potentials for a
vehicle-based data collection and local dissemination of information. By means
of microscopic traffic simulations we study the problem of online estimation of
the current traffic situation based on floating car data. Our focus is on the
estimation on the up- and downstream jam fronts determining the extension of
traffic congestion. We study the impact of delayed information transmission by
short-range communication via wireless LAN in contrast to instantaneous
information transmission to the roadside units by means of mobile radio. The
delayed information transmission leads to systematic estimation errors which
cannot be compensated for by a higher percentage of probe vehicles. Additional
flow measurements from stationary detectors allow for a model-based prediction
which is effective for much lower floating car percentages than 1%.
