Trip

# randomTrips.py

"randomTrips.py" generates a set of random trips for a given network (option -n). It does so by choosing source and destination edge either uniformly at random or with a modified distribution as described below. The resulting trips are stored in an XML file (option -o, default trips.trips.xml) suitable for duarouter which is called automatically if the option (with a filename for the resulting route file) is given. The trips are distributed evenly in an interval defined by begin (option -b, default 0) and end time (option -e, default 3600) in seconds. The number of trips is defined by the repetition rate (option -p, default 1) in seconds. Every trip has an id consisting of a prefix (option --prefix, default "") and a running number. Example call:

    python tools/randomTrips.py -n <net-file> -e 50

The script does not check whether the chosen destination may be reached from the source. This task is performed by the router. If the network is not fully connected some of the trips may be discarded.

The option --min-distance <FLOAT> ensures a minimum straight-line distance (in meter) between start and end edges of a trip. The script will keep sampling from the edge distribution until enough trips with sufficient distance are found.

## Randomization

When running randomTrips.py twice with the same parameters, the same results will be created because the random number generator is initialized with the same value. To get "true" randomness (always a different output) use the option --random. The option --seed <INT> can be used to set an initial value and get different but still repeatable pseudo-randomness.

## Edge Probabilities

The option --fringe-factor <FLOAT> increases the probability that trips will start/end at the fringe of the network. If the value 10 is given, edges that have no successor or no predecessor will be 10 times more likely to be chosen as start- or endpoint of a trip. This is useful when modelling through-traffic which starts and ends at the outside of the simulated area.

The probabilities for selecting an edge may also be weighted by

- edge length (option -l),
- by number of lanes (option -L)
- edge speed (exponentially, by option --speed-exponent)
- generic edge parameter (option --edge-param)
- direction of travel (option --angle-factor and --angle)

For additional ways to influence edge probabilities call

    python tools/randomTrips.py --help

## Traffic Volume / Arrival rate

The arrival rate (also known as the departure rate or the insertion rate) is controlled by option --period <FLOAT> (default 1). By default this generates vehicles with a constant period and arrival rate of (1/period) per second. By using values below 1, multiple arrivals per second can be achieved. If several <FLOAT> numbers are passed, like in --period 1.0 0.5 (or --period="1.0,0.5") for example, the time interval will be divided equally into subintervals, and the arrival rate for each subinterval is controlled by the corresponding period (in the preceding example, a period of 1.0 will be used for the first subinterval and a period of 0.5 will be used for the second). There are two other ways to specify the insertion rate:

- Either by using the --insertion-rate argument (with one or several values as explained before): this is the number of vehicles per hour that the user expects.
- Or by using the --insertion-density argument (with one or several values): this is the number of vehicles per hour per kilometer of road that the user expects (the total length of the road is computed with respect to a certain vehicle class that can be changed with the option --edge-permission).

When adding option --binomial <INT> the arrivals will be randomized using a binomial distribution where n (the maximum number of simultaneous arrivals) is given by the argument to --binomial and the expected arrival rate is 1/period (this option is not yet available in version 0.23.0).

### Example

To let n vehicles depart between times t0 and t1 set the options

    -b t0 -e t1 -p ((t1 - t0) / n)

Note

The actual number of departures may be lower if the road capacity is insufficient to accommodate that number of vehicles or if the network is not fully connected (in this case some of the generated trips will be invalid).

## Insertion Distribution

The number of inserted vehicles (if all trips are valid) is fixed for a given set of randomTrips option: `(end-begin)/period`. Randomness appears in the insertion pattern on any given edge.

By default the departures of all vehicles are equally spaced in time. Since the inserted vehicle are spread randomly over the whole network, this comes out as a binomial distribution of inserted vehicles for each individual edge which gives a good approximation to the Poisson distribution if the network is large (and hence the insertion probability of each edge is small).

By setting set option --random-depart, the (still fixed) number of departure times are drawn from a uniform distribution over `[begin, end]`. This leads to an exponential distribution of insertion time headways between vehicles on all edges (which is the headway pattern of the Poisson distribution). Hence, this is useful to have a more varied insertion time pattern for small networks.

## Validated routes and trips

When using the option --route-file, an output file with valid vehicle routes will be generated. This works by automatically calling duarouter in the background to turn the random trips into routes and automatically discard disconnected trips. It may be necessary to increase the number of generated random trips to account for a fraction disconnected, discarded trips.

Caution

When using the option --vehicle-class the same value should be set for option --edge-permission

Sometimes it is desirable to obtain validated trips rather than routes (i.e. to make use of one-shot route assignment. In this case the additional option --validate may be used to generate validated trips (by first generating valid routes and then converting them back into trips).

## Generating vehicles with additional parameters

With the option --trip-attributes <STRING>, additional parameters can be given to the generated vehicles (note, usage of the quoting characters).

    python tools/randomTrips.py -n <net-file>
      --trip-attributes="departLane=\"best\" departSpeed=\"max\" departPos=\"random\""

This would make the random vehicles be distributed randomly on their starting edges and inserted with high speed on a reasonable lane.

Note

Quoting of trip attributes on Linux may also use the style --trip-attributes 'departLane="best" departSpeed="max" departPos="random"'

### Setting a vehicle type from an external file

If the generated vehicles should have a specific vehicle type, an additional-file needs to be prepared:

    <additional>
      <vType id="myType" maxSpeed="27" vClass="passenger"/>
    </additional>

Then load this file (assume it was saved as type.add.xml) with the option --additional-file

    python tools/randomTrips.py -n <net-file> --trip-attributes="type=\"myType\"" --additional-file <add-file>
       --edge-permission passenger

Note the use of the option --edge-permission (deprecated alias: --vclass) which ensures that random start- and arrival-edges allow a specific vehicle class.

To generate random pedestrian traffic instead of vehicular traffic, the option --pedestrians may be used. It is recommended to combined this with the option --max-distance to avoid walks of excessive length. See Simulation/Pedestrians for addition information on the simulation of pedestrians.

Note that the option --vehicle-class should only be used as a quick shorthand to generate trips for the standard type of the given vehicle class since it places a standard vType definition in the generated trips file.

### Automatically generating a vehicle type

By setting the option --vehicle-class a vehicle type definition that specifies vehicle class will be added to the output files. I.e.

    python tools/randomTrips.py --vehicle-class bus ...

will add

    <vType id="bus" vClass="bus"/>

Any --trip-attributes that are applicable to a vehicle type rather than a vehicle will be placed in the generated `vType` definition automatically:

    python tools/randomTrips.py --vehicle-class bus --trip-attributes="maxSpeed=\"27.8\""

will add

    <vType id="bus" vClass="bus" maxSpeed="random"/>

Alternatively, after randomTrips.py has finished, the created `<vType>`-element can be edited to specify additional parameters. The downside of manual editing is that it must be repeated when running randomTrips.py again.

## Generating different modes of traffic

- Using the option --pedestrians will generated pedestrians instead of vehicles.
- Using the option --persontrips will generated persons with `<persontrip>` definitions. This allows to specify the available traffic modes and thus use IntermodalRouting to decided whether they use public transport, a personal car or walking.
  - walking or public transport: --trip-attributes "modes=\"public\""
  - walking, public transport or car --trip-attributes "modes=\"public car\""

Caution

Quoting of trip attributes on Linux must use the style --trip-attributes 'modes="public"'

## Intermediate Way Points

To generate longer trips within a network, intermediate way points may be generated using the option --intermediate <INT>. This will add the given number of via-edges to the trip definitions.

## Customized Weights

### Saving

Using option weights-output-prefix <STRING> will cause three weight-files with the given prefix to be generated (<prefix>.src.xml, <prefix>.dst.xml, <prefix>.via.xml) which contain the used edge probabilities.

- .src.xml contains the probabilities for an edge to be selected as `from`-edge
- .dst.xml contains the probabilities for an edge to be selected as `to`-edge
- .via.xml contains the probabilities for an edge to be selected as `via`-edge (only used when option --intermediate is set).

### Visualization

Any of these files can be loaded in sumo-gui for visualization

### Loading

Files in this format can be used to set customized weights for generating random trips by using the option --weights-prefix <STRING> with the prefix value as argument. The randomTrips script will attempt to load weights for all edges and all three file extensions (.src.xml, .dst.xml, .via.xml) but will use the following defaults if same values are missing:

- If a loaded weight file does not contain all edges, probability 0 will be assumed for the missing edges
- If a file is missing, the probabilities according to the regular options are used when sampling that type of edge (i.e. missing <prefix>.dst.xml will result in probabilities as described in section #Edge_Probabilities will be used when sampling destination edges)

Note

Probabilities loaded from the weight-files are automatically normalized. Therefore it does not matter whether probabilities are specified as fractions or percentage values.

### Usage Example

To obtain trips from two specific locations (edges a, and b) to random destinations, use

    python tools/randomTrips.py --weights-prefix example  ...<other options>...

and define only the file example.src.xml as follows:

    <edgedata>
      <interval begin="0" end="10"/>
        <edge id="a" value="0.5"/>
        <edge id="b" value="0.5"/>
      </interval>
    </edgedata>

## Forwarding options to duarouter

When generating the route .rou.xml file, duarouter is called. Some arguments are already passed to duarouter directly from arguments received by randomTrips. However, should you need so, you can directly pass an argument to duarouter with the syntax `--duarouter-option value`; for instance using `--duarouter-exit-times true` with randomTrips will forward the argument `--exit-times` to duarouter when it is called, and with the value `true`. Please note that it is compulsory to pass a value together with the option, for instance `--duarouter-exit-times` wouldn't be valid in this context.

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