Vehicle Models

Caution

Please note that this is a working document... No user documentation!

# Implementing new Car-Following Models

A car-following model in SUMO is an implementation of the abstract class MSCFModel (microsim/cfmodels/MSCFModel.h).

The following steps must be taken to add a new model:

1. define a new model name in utils/common/SUMOXMLDefinitions.h and .cpp
2. define model parameters in utild/xml/SUMOVehicleParserHelper::getAllowedCFModelAttrs() (define new attributes in SUMOXMLDefinitions if necessary)
3. add a new class to microsim/cfmodels (i.e. by copying one of the existing classes there)
4. add this class to the build files (i.e. microsim/cfmodels/Makefile.am when building on Linux)
5. add code that selects the new class based on the new name in microsim/MSVehicleType::build()

If your model needs persistent state you need to derive a class to hold it from MSCFModel::VehicleVariables. See microsim/cfmodels/MSCFModel_IDM as an example.

# Defining Vehicle Types

Before starting to hack, we should decide how vehicle type shall be represented. Some facts and needs (unsorted):

- ok Both the simulation and the routing modules must be able to parse vehicle type definitions
- It would be nice to allow a validation against XML Schemata
- At least two sub-types must be able to be defined: car-following model and lane-changing model (maybe the lane-changing model even splits into a navigational and a tactical part)
- ok Parameter should have default values
- ok a default vehicle type must exist
- Models differ in parameter sets

## Possible Descriptions

Index | Sample | pros/cons
--- | --- | ---
A | <vtype cfModel="xxx" xxxParam1="..." xxxParam2="..." ... | (-) hard to verify - parameter change in dependence to the value of "cfModel"
B | <vtype-XXX xxxParam1="..." xxxParam2="..." ... | (-) large number of different elements needed
C | <cfmodel id="#id" model="xxx" param1="..." param2="..." .../> <vtype cfModelId="#id" .../> | (+) straight forward; many combinations possible (+) is similar to how every vehicle references its vtype (-) hard to verify - parameter change in dependence to the value of "cfModel"
D | <vtype cfModel="xxx" param1="..." param2="..." ...> | (--) parameter sets differ between models (-) hard to verify - parameter change in dependence to the value of "cfModel"
E | <vtype ...> <cfmodel model="xxx" param1="..." param2="..." .../> | (+) straight forward (-) hard to verify - parameter change in dependence to the value of "cfModel" 1 vote (Mayer)
F | <vtype ...> <cfmodel-XXX model="xxx" param1="..." param2="..." .../> | (+) straight forward (-) large number of different elements needed 2 votes (Behrisch, Krajzewicz)

## (currently) Chosen Description

After some talks, the following description of vehicle types was chosen:

    <vtype id="..." ...>
        <carFollowing-Krauss ... >
        <laneChanging-DK2002 ... >
    </vtype>

`vtype` will contain parameters which can neither be counted to the lane-changing nor the car-following model, such as the vehicle type's color, the width of the vehicle etc. which are (currently) used for visualisation only. Also, the vehicle's length and other parameter which are not only used by one of the models are stored herein.

The embedded `carFollowing-Krauss`-Element in this example describes the car-following model (Krauss in this case), the `laneChanging-DK2002` the lane-changing model (Daniel Krajzewicz's from 2002 :-) ), each with their own parameter.

The known `vtype`-definition is wanted to be kept. In this case, the Krauss-model stays chosen per default.

Note

Probably, it will not be possible to validate this against a schema.

# Car-following Model Interface

Currently, it is assumed that the following methods should be re-implemented for each model; the "generic" column should identify those which may be same across models:

method | generic? | description
--- | --- | ---
ffeV | no |
ffeS | no |
maxNextSpeed | no | internal SUMO-tweak
brakeGap | maybe | should depend on maximum deceleration (a rather common value) and physics, only
approachingBrakeGap | maybe | almost same as brakeGap, only not incorporating the driver's reaction time
interactionGap | no |
hasSafeGap | no |
safeEmitGap | no |
dawdle | no |
decelAbility | rather no |

## Loading and Parsing Vehicle Types

As already implemented for vehicles, a new intermediate structure <SUMO_HOME>/src/utils/common/SUMOVTypeParameter which contains vehicle type descriptions was added. When reading XML-definitions, both routers and the simulation use the additionally implemented helper methods located in <SUMO_HOME>/src/utils/xml/SUMOVehicleParserHelper for filling this structure.

SUMOVTypeParameter has member variables for those vehicle type parameters which are assumed to be neither part of the car-following model nor part of the lane-change model: id, length, maxSpeed, defaultProbability, speedFactor, speedDev, emissionClass, color, vehicleClass, width, offset, shape. These values are initialised with defaults. When reading values, SUMOVehicleParserHelper stores the information about which value was set from the XML description in SUMOVTypeParameter::setParameter. This allows to save (pass) only set values when writing the definitions back to a file - routers need this.

Parameters of the car-following model are saved into a map, SUMOVTypeParameter::cfParameter, the model's name to SUMOVTypeParameter::cfModel. Note that lane-changing model parameter handling is not implemented. The map contains only those parameter of the model which were given in the read XML file; no defaults are inserted at this time. In order to allow processing of old vtype-definitions, parameter stored directly within the vtype-element for the Krauss car-following model are stored within this map, too.

The routers consume the SUMOVTypeParameter class directly - making ROVehicleType unnecessary. The simulation uses the new method MSVehicleType::build for building the described MSVehicleType/MSCFModel combination. Missing defaults are set within this method for obtaining complete vehicle type/model descriptions.

#### Search

Enter your search terms:

#### Keyboard Shortcuts

Key | Action
--- | ---
`?` | Open this help dialog
`s` | Search the Documentation
`e` | Edit current page on GitHub