Vehicle following in an automated transit system is a longitudinal control scheme where the state of a given vehicle is determined by the behavior of the preceding vehicle. At short time headways (0.5 to 3.0 s) a kinematic constraint on vehicle operation arises as a consequence of the velocity, acceleration, and jerk limits imposed to assure passenger comfort. This constraint requires a trailing vehicle to maintain a spacing such that it may react to nominal (nonemergency) preceding vehicle maneuvers without collision and without exceeding service jerk and acceleration limits. The large initial conditions which may result preclude the use of linear time-invariant feedback. Thus a nonlinear feedback controller is designed which forces the vehicle to follow the kinematically required spacing until the desired headway is attained. The design is based upon a technique which uses an approximately optimal feedback control with state constraints. In addition, several suboptimal controls with reduced informational requirements are presented, thus producing an easily instrumentable controller which properly responds to all possible nominal maneuvers of a preceding vehicle.

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