BASim SIMULATION PROGRAM
This simulation program has been used by Austrans to assist the design and testing of alternative networks
and operating policies for their Group Rapid Transit (GRT) technology.
As stated in the following abstract from Appendix E of Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO) 2002 report The RTSim simulator has been developed to model dedicated guideway mass public transport networks. The simulator can be configured to model a variety of group rapid transit and personal rapid transit systems. It is a discrete event simulator; written in Java script and it can run on a variety of computer platforms.
A description of the principal attributes of the simulator follows.
A network comprises nodes and links.
A node is a geographical point. A node may have a speed limit associated with it, as well as one or more decision points.
A link connects two nodes, representing a section of the network guideway. A link has attributes namely:
Rated maximum speed; and
A link also has a type. The link types are:
A switch is the type of link used when two links merge or diverge. Passenger groups appear at a station according to an arrival process. They queue for service and board vehicles as instructed. Arrivals may be at fixed intervals, or according to a predetermined statistical distribution. A platform can be off-line or on-line and models the loading and unloading of passengers. The number and position of berths can be specified. The destinations of passengers boarding at a particular platform may be limited and a platform may be specified as no set-down. A siding models a parking area to which vehicles can be moved when out of service.
Routes, which comprise lists of stations in the order in which a vehicle must visit them, are also part of the modelling process. Position objects are associated with switches and record the switch position to be set for specific destinations. Decision points are associated with platforms, stations or sidings and appear at a node some distance before the switch which controls entry to the platform, station or siding.
Vehicle motion and control
The vehicle is the main object in the simulation. Each vehicle has a vehicle type, which specifies parameters such as vehicle size, number of doors, passenger capacity, maximum speed, maximum acceleration, comfortable deceleration and the time needed to open and close the doors.
Vehicles move between links by performing manoeuvres. A manoeuvre describes the plan for the next time period, such as accelerate to a specified speed or stop at a given point.
There is a separate vehicle controller class for each type of link. The basic vehicle controller manages vehicle speeds. In addition an off-ramp controller ensures that an off-ramp link has sufficient space for an approaching vehicle to enter and, if necessary, brakes the vehicle; a station controller controls vehicle movements within a station; a siding controller controls vehicles within a siding; and a switch controller controls vehicles within a switch. A single network controller handles higher-level decisions.
The simulation model includes algorithms for:
Empty vehicle routing;
Boarding passenger selection;
Use of sidings; and
Three different merge priorities are currently availablea mainline policy that gives priority to the mainline, a merge policy that gives priority to vehicles on on-ramps and a platoon policy that gives first priority to a platoon (a group of vehicles with a common destination) approaching on the mainline.
BASim is configured using plain text files. The configuration files are summarised in Table 30 below:
File Use Main configuration file Sets parameters for the entire simulation, including the names and locations of other configuration files. Node list Describes the nodes (end points of links and walkways, and the corners of platforms) in the network and their location. Link list Describes the links (sections of track) in the network. Switch position list Describes the nodes that switches can point to and routing information. Station colours (optional) Lists colours to use when drawing platforms, passengers and vehicles. Route information (optional) Lists any routes that the vehicles should follow and the timetables they should adhere to. Vehicle types Describes the kinds of vehicles in the simulation. Headway data (optional) Gives interpolation points for headway between vehicles and before switches. Distributions (optional) Describes distributions for random variables, which can be used in other configuration files. Vehicle list Lists vehicles in the simulation, their start points and their type. Passenger arrivals Describes the distribution with which passengers appear at stations to start a trip and their destinations. Decision point list Lists the points on the track where a vehicle must make one of a number of decisions. Siding decision point list Lists the points on the track where a vehicle must decide whether or not to park at a siding. Backdrop information (optional) Describes the images to display behind the track for orientation.
The main configuration file contains options that set the behaviour of the simulation as a whole as well as options to control output. The groups of options included in the main configuration file are:
GUI (graphical user interface) options;
Report options; and
There are two main types of reports from BASim:
A report containing periodic summary data from the BASim run. The file contains a number of interim reports and a final report;
A file containing reports of individual events that can be used to obtain more detailed statistics of the simulation run.
The following concepts are used in the reports:
Tripa vehicle journey from station to station;
Empty tripa trip from station to station carrying no passengers;
Hopa trip as seen from a passengers perspective. Each stop at an intermediate station is a hop;
Occupancynumber of passengers on board a vehicle;
Mean occupancytotal passengers carried divided by the number of trips;
Travel timetime from vehicle doors closing at one station to opening at the next;
Wait timetime from a passengers arrival on a platform until boarding a vehicle;
Maximum waitthe maximum time spent waiting among all passengers waiting on a platform;
Journeythe total travel of a passenger within the system. A journey may consist of one or more trips, with changes of vehicles. The journey time is the total time the passenger spends within the system from arriving at the first station to alighting from the vehicle at the last station.
Dwell timethe length of time spent stopped at a station, waiting for passengers to alight and board etc;
Delaydifference between actual journey time and an idealised minimum time;
Number of destinationsthe number of distinct destinations of passengers aboard a vehicle each trip;
Mean destinationsthe sum of number of destinations each trip divided by the total number of trips;
Powerthe amount of power used by vehicles during the simulation period. BASim uses a simplified acceleration and deceleration model and does not take account of regenerative braking, so the output is an approximation only to actual power consumption;
Wave-offthe situation where a vehicle cannot enter an off-line station due to congestion and is sent instead to its next destination;
Traverse timethe time a vehicle takes to run the length of a link; and
Switch gapthe length of time between starting one switch action and the time the next switch operation commences.
The interim report covers only activity during the most recent report interval. The final report covers activity during the whole simulation run (excluding the warm-up period).
The main part of the report is divided into sections covering:
The following events can be logged to file:
Passenger boardeda passenger has boarded a vehicle. Wait time is logged;
Journey finishedvarious journey statistics are logged;
Power consumption (a continuously changing value)instantaneous and total power consumption are logged;
Distance (a continuously changing value)the total distance covered by all vehicles is logged;
Scheduled vehicle arrivala vehicle running a fixed route with a schedule has arrived at a station; and
Test divert eventa vehicle is being tested to see if it should divert to one or more platforms.
Last modified: April 13, 2004