Auto Network - tlumip/CALM GitHub Wiki
Important Note - the User only edits the network inputs in the Visum version file in the "Visum" input folder. The name of that version file is specified in inputs\settings.csv.
The following are critical link attributes the user must be aware of:
- TypeNo - (type number) This attribute can be used to set default link attributes for each type number. In JEMNR, the type number used also needs to match the Volume delay function number ( VDF ) to be applied to the link
- TSysSet - set of allowed transportation systems/modes
- NumLanes - number of lanes (in the direction of travel)
- Length - the user input length of link segment (should almost always be the geometric length, but this is a user input field that is not required by the software to be the actual length of the link, so the user needs to be intentional and review these lengths for correctness).
-
PlanNo - Visum's "Planning Number" attribute is used to hold the Functional Classification tag. The following are the function classes used in JEMnR;
- Interstate = 1
- Principal Arterial = 2
- Minor Arterial = 3
- Collector = 4
- Local = 5
- Ramp = 30
- Non-Auto (bike/ped) link connection = 100
- V0PrT - free-flow speed for private transport systems (non-transit vehicles)
- CAPPERLANE - Hourly per lane capacity. Users update this field for scenarios that involve changes to capacity. This field will update CapPrt as is described below.
- CapPrT - [Calculated within Visum Procedure - not a user input] Directional capacity for private transport systems (non-transit vehicles). The directional capacity is calculated from hourly per-lane capacity and number of lanes (NumLanes) as CapPrt is a cross-sectional capacity.
- T0ForPuT - [Calculated within Visum Procedure - not a user input] This field holds a different (longer) link travel time for buses than autos - taking into account number of stops and dwell times. This field requires the LineRouteItems attributes EMME_TTF_FACTOR. This field is calculated with the following visum equation: IF([MAX:LINEROUTEITEMS\EMME_TTF_FACTOR] > 0,(([LENGTH] / [V0PRT]) * 60) / [MAX:LINEROUTEITEMS\EMME_TTF_FACTOR],([LENGTH] / [V0PRT]) * 60)
| TSys code | Name | Description |
|---|---|---|
| a | Auto | Used for private autos and commercial vehicles in highway assignment. Links are open to the a TSys in the direction where motor vehicle traffic is allowed. Most connectors are open to autos, except transit connectors. |
| b | Bus | Links are open to the b TSys where bus routes operate. |
| w | WalkToTransit | Links are open to the w TSys where walking should be allowed between transit stops. This is especially important where multiple bus routes operate in close proximity. Additionally, special connectors or stops representing the shorter walk distance for transit coverage area will be coded "w". |
| Walk | Walk | All links should be open to the walk TSys except where prohibited, such as freeways and Interstates. The walk demand segment is not assigned, but available walk paths are skimmed in Visum. |
| Bike | Bike | Most surface street links should be open to the bike TSys except in the prohibited direction on one-way streets and where prohibited, such as freeways and Interstates. Like walk demand, the bike demand segment is not assigned, but available bike paths are skimmed in Visum. |
Link capacities are calculated during the model run from the per-lane hourly capacity, CAPPERLANE, and are set by running either set_daily_capprt.xml or set_peak_capprt.xml procedure before assignment. For peak period skim and assignment procedures, the CapPrT is set to CAPPERLANE × NUMLANES. For daily skim and assignment procedures, CapPrT is set to CAPPERLANE × NUMLANES × 16.
Note: Each turn move must have the TSYSSET(s) designated to it to which it is open, otherwise that turn will be closed to that mode. This must be done for all TSYSSET values which apply to the turn.
There are 5 VDFs in use for auto assignment in Visum. The VDF used in assignment is determined by the link's Type Number. Links with Type 1 use VDF number 1. The equations based on the standard Bureau of Public Roads (BPR) function are defined in the table below:
| VDF No | Function | Segment Function |
|---|---|---|
| 1 | tcur = t0 × (1 + 0.05 × (v/c)10) | Signalized |
| 2 | tcur = t0 × (1 + 0.83 × (v/c)5.5) | Interstate |
| 3 | tcur = t0 × (1 + 0.56 × (v/c)3.6) | Ramp |
| 4 | tcur = t0 × (1 + 0.83 × (v/c)2.7) | Principal Arterial |
| 5 | tcur = t0 × (1 + 0.71 × (v/c)2.1) | Other Facilities |
where tcur is the congested travel time, t0 is the free-flow travel time, and v/c is the volume-to-capacity ratio.
In Visum, VDFs are stored as part of the skimming and assignment procedure sequence definitions. Follow these steps to verify and/or modify the VDFs used in assignment:
- Open the input version file (typically in the
/visumfolder) in Visum. - Open the procedure sequence window, which is a way of creating macros in Visum's GUI for repeated tasks or to implement a complete demand and assignment model.
- Click on the Open folder icon to open the auto assignment procedure file, located at
/visum/procedures/prt_assignment.xml. - Click on the General Procedure Settings icon to open the dialog box.
- Expand the PrT settings section and click on Links VD Functions. As necessary modifications to the functions can be made. But at the time of this wiki, the procedure files should align with the values and equations captured above.
- Save any changes to the procedure sequence by clicking on the save icon within the procedure sequence window. Generally, ensure that settings are the same between skimming and assignment procedures. Do not save the version file. The procedure sequence within the version file should remain empty to avoid issues with future model runs and prevent accidental modifications to output files, such as accidentally running an assignment procedure.
Note - similar to turn moves, connectors can only be used for the TSYSSET (modes) identified. Modes can be turned on or off at the connector level.
Centroid connector times are calculated by the procedure; connector_times.xml. This sequence uses the connector attributes LENGTH and SPEED (auto link). Bike and walk connectors use default speeds of 10mph and 3 mph respectively. For auto modes, the treatment in Visum is to assume a global speed setting for centroid connector links (the default speed starts at 31 mph, but can be set at anything, typically 25 mph for Oregon models). In the Emme implementation of CALM, Centroid connectors have individually-set custom speeds. To replicate this in Visum, connector times (t0) can be calculated based on a per-connector speed variable.
In the centroid connectors list, the Emme_Data1 variable is the connector speed in miles per hour transferred from Emme. The Connector Times procedure calculates connector times in seconds using this speed for autos:
Auto connector t0 = ([LENGTH]/[EMME_DATA1])*60*60
Length (in miles) divided by speed (in miles per hour) yields travel time in hours, which is then multiplied by 60×60 to yield time in seconds.
Connector times for other modes use fixed speeds of 10 mph for bikes and 3 mph for walking:
Bike connectors: t0 = ([LENGTH]/10)*60*60
Walk and WalkToTransit connectors: t0 = ([LENGTH]/3)*60*60
If setConnectorTimes in the Settings file is TRUE, the connector_times.xml procedure will run before skimming and assignment. The procedure can also be run on the input version file or times can be updated manually. If this is the case, disable the automated procedure by setting setConnectorTimes to FALSE.
The CALM auto network, representing Interstate, highways, and arterial roads in the region, was transferred from Emme to Visum use the import function in Visum.