A Recursive Method for Traffic Management through a Complex Path Network

Many simulation models contain one or more transport systems where some type of vehicle, perhaps an AGV, a fork truck, a shuttle, or a human being, travel along predefined paths. Locations along the paths may specify where loads carried by the vehicle transfer to or from it, where some activity takes place requiring the vehicle’s presence, or where vehicle routing logic executes. This paper focuses on the last topic, the routing of vehicles along a path system where alternate paths exist and path selection is determined at so called “routing nodes” based on a dynamic analysis of traffic congestion along each possible route towards some destination. Other routing nodes further along each path present more combinations of possible interim paths. A recursive search algorithm is presented to iteratively evaluate each possible route when a vehicle encounters a routing node. The vehicle is directed along a path with the least overall congestion towards its destination. A sample model demonstrating this algorithm implemented in the AutoMod software is used for illustration. Other simulation products may have the features to support this type of vehicle routing control algorithm. 1 AUTOMOD’S PATH MOVER SYSTEM The AutoMod simulation software contains a material handling system called the Path Mover, in which vehicles move along guidepath, carrying loads from pickup locations to delivery locations (called “control points”). Path Mover vehicles can represent manually operated lift trucks, people, or computer-controlled vehicles (any type of movement system in which vehicles follow a specific path or route). By default, AutoMod vehicles in a Path Mover system use the shortest route between load pickup and delivery points. Where intersections offering more than one path segment to another control point exist, the default routing can be over-ridden by using a built-in “location selection function”. This function defines the next control point a vehicle claims in its route, or if the next path segment is blocked, the transfer (a construct automatically inserted by AutoMod at path intersections) may offer an alternate path. 1.1 Location Selection Function Path Mover vehicles automatically call the location selection function each time they have a choice of determining the next control point to claim on the way to their destination. The function provides the opportunity to select from a list of subsequent control points to the current location and returns the control point to which the vehicle will travel next (returning null from the function will direct the vehicle to take the shortest route to its destination, the default). The location selection function is a convenient way to make local decisions for vehicle routing. begin pm location selection function choose a location from among theLocList whose remaining space is maximum save choice as Vchoiceloc return Vchoiceloc