  If a bus line becomes unstable, passengers waiting time will be lengthened
and buses capacities will be mismatched. To stabilize a high-frequency bus
line, many holding strategies have been proposed. Among these strategies, some
need to take oversimplified assumptions to simplify the formulation of a real
bus line; some may choose a myopic holding time because they take into account
only the local and currently available headway information. To overcome the
above shortcomings, we proposed an adaptive holding strategy which continuously
reduces the deviations of the instantaneous headways from the Dynamic Target
Headway -DTH. By using DTH, the new strategy can make use of the global headway
information to determine a proper holding time. To fully estimate the influence
of a holding time on the operation of a bus line in a relative long time
period, we introduced the multi-stage looking-ahead mechanism into our new
strategy. A detailed bus line simulation system was used to realize the above
mechanism and to describe all kinds of complex components of a bus line. The
numerical experiment demonstrated the effectiveness of our new strategy. Some
meaningful insights were uncovered as follow: a. The number of stages to be
looked ahead should not be too small or too big; b. The bigger the range of the
action set, the better the performance of our strategy; c. To obtain the
optimal performance, the interval between two neighbor holding times should not
be too small or too big; d. the bigger the number of the control points, the
better the performance of our strategy.
