In the past，the research of traffic information system is mainly carried out in static transportation networks，and the dynamic behavior of travelers under the guidance of real time traffic information is rarely studied． In this paper，the dynamic reaction of travelers and the non-equilibrium traffic evolution in transportation networks under the guidance of traffic information are studied，based on which the benefit of traffic information is evaluated． Firstly，we investigate three kinds of travel behaviors: simultaneous departure time and route choices of drivers in normal traffic condition，travel behavior of drivers without traffic information after a traffic accidents occurring，and travel behavior of drivers with real time traffic information guidance after a traf-fic accidents occurring． By comparing the total travel costs in the three situations，the change of the total travel cost or the benefit of traffic information can be calculated． It is found that traffic information system can miti-gate traffic congestion of networks substantially，if the traffic accident is severe and road capacity drops heavi-ly． However，if the traffic accident is light and road capacity drops slightly，providing traffic information will make transportation system worse off，and it will resut in the increase of total travel cost． This implies that traf-fic information is not always good to transportation system，and it should be provided cautiously．