The Tour planning procedure links the demand, i.e. the generated trip requests, with the supply, i.e. the vehicle fleet and the pickup and dropoff points. It is based on the routing-enabled network of the transport model, i.e. on the open links and turns of its PrT reference transport system.
It is based on the routing-enabled network of the transport model, i.e. on the open links and turns of its PrT reference transport system.
This procedure is divided into two steps:
- The preselection of vehicles
- The actual dispatching
In the preselection, a bounding box is drawn up in the area under investigation, which is formed by the maximum coordinates of the From-nodes, pick-up and drop-off nodes, and To-nodes of all relevant trip requests, as well as the loading and holding areas. This is divided into a grid of 20x20 sectors. An internal travel time matrix is calculated. The preselection now determines the sectors that can theoretically meet the pick-up window of a trip request. The vehicles in these sectors are used for dispatching.
The dispatching algorithm allocates open trip requests to the available vehicles. The trip requests are known to the dispatcher from the time they are created and are scheduled immediately. The algorithm finds the vehicle with the lowest additional costs in order to plan the respective trip request and the best insert position in the respective tour.
Whether a vehicle is available depends on the vehicle capacity, the current location, and the passengers currently being transported. The service promise for the detour time to passengers already transported must allow the additional time for a new journey to be planned.
The additional time for serving a new trip request is calculated from the new travel and stop time resulting from new pick-up and drop-off activities:
To minimize the number of vehicles used, vehicles that are still at the initial starting point and have not yet been assigned a trip request are multiplied by a factor in the calculation of additional time, which represents the activation costs of adding an extra vehicle to the fleet. This factor depends on the utilization of the maximum fleet size and a coefficient that can be set by the user:
The vehicle with the shortest additional time ET is selected to serve the trip request. If no vehicle is available or does not meet the conditions for the maximum wait time of the trip request, the passenger will not be transported.
The number of vehicles and insert positions in the tour can be limited in advance. To avoid unnecessarily increasing the duration of the procedure, the vehicles in the sector in which the trip request was made are checked first. If vehicles are already available here, additional sectors are optionally not checked.
The pick-up and drop-off points of the trip requests are determined by the dispatcher. The candidates for these locations are defined by the set maximum number and the maximum PuT Walk access time from the start or end point to the pick-up or drop-off point. Increasing these parameters increases flexibility in dispatching. The selection of suitable drop-off and pick-up point pairs is controlled by a cost function. The coefficients of this cost function weight the requirements for efficient operation of the fleet ( = shorter additional travel time) and service comfort for passengers ( = shorter access and egress routes).
Vehicles that do not receive new orders after submitting a trip request return to holding areas after an adjustable time. During the relocation and at the holding area, the vehicle is available to serve trip requests. The selection of the holding area influences the future availability of the vehicle due to its location.
The choice of the holding area is determined, among other things, by the distance to the respective location of the vehicle. However, it is a
The attraction of the holding areas increases when a trip is requested nearby or a vehicle leaves the holding area. The attractiveness of the holding area decreases when the last served trip request of a vehicle ends in the area of the holding area. It is zero when its vehicle capacity is exhausted.
The reason for considering future trip requests is that providers have a demand forecast that will direct vehicles to subsequent peak demand points.
Tour planning results
The tour plan calculated is aggregated in various ways and adopted into the transport model.
The paths of the passengers are saved as PuT paths. Each path contains three path legs: one arrival path, one departure path and the path leg calculated that was covered using the responsive transport system. This path leg represents both the possible detour as well as the wait time for dropping off or picking up other passengers. From the total of these paths, skims are derived, analogous to conventional PuT.
For adjacent zones, the random distribution of trip requests at the node level can result in trip requests receiving the same pickup as well as dropoff point. These special cases are then represented by a public transport path composed only of walk links. The passengers with this trip request reach their destination this way. The tour planning of the fleet, however, remains unaffected by such pure walk links.
Due to the stochastic disaggregation of the trip requests, skims should only be used after multiple calculations of tour planning, taking into account various seed random numbers for trip request generation.
In addition, the trips of each vehicle are saved to a specified path set. They are used as a basis for estimating the operating expenses. PrT paths are created gradually by servicing pickup and dropoff points. The paths between these nodes are determined via a shortest path search. The resulting volume can be saved as a link attribute.
The individual pickup or dropoff points of a tour can be linked to a zone, just as for trip request generation via shortest path search. This allows you to create a PrT demand matrix that consists of individual legs of the tour. The subsequent assignment of such a matrix to an existing network creates a more realistic picture of the network volume generated through demand responsive transport.
