4.2 Network Skims

Highway and transit skims are created by Visum skimming procedures. These are then used as inputs by DaySim during day pattern simulation.

Highway Skims

The skims generated by the Calculate PrT skim matrix procedure are stored in the Visum version file. These are then exported into the format required for DaySim by the export_all_hwy_skims.py and export_{period}_hwy_skims.py Python scripts.

DaySim requires skim files in text format which are created in a step in “DaySim” application. All the skim files are output to the following folder: Master\{SCENARIO_DIR}\Output\DaySim\.

Following are highway skim files created: SKM_AM_D1.TXT, SKM_AM_S2.TXT, SKM_AM_S3.TXT, SKM_MD_D1.TXT, SKM_MD_S2.TXT, SKM_MD_S3.TXT, SKM_PM_D1.TXT, SKM_PM_S2.TXT, SKM_PM_S3.TXT, SKM_EV_D1.TXT, SKM_EV_S2.TXT, SKM_EV_S3.TXT. All the files are space-delimited and do not have any headers. Table 4‑1 shows the structure of the files.

TABLE 4-1 HIGHWAY SKIM FILE FORMAT

Column #	Name
1	Origin TAZ
2	Destination TAZ
3	Time (min)
4	Distance (miles)
5	Cost ($)
6	Crossriver
7	Intra-county factor

SKM_NM.TXT is the non-motorized modes skim file. DaySim uses free flow shortest path distance with an average time of 20 minutes per mile for walk and 6 minutes per mile for bike.

TABLE 4-2 NON-MOTORIZED SKIM FILE FORMAT

Column #	Name
1	Origin TAZ
2	Destination TAZ
3	Time bike (min)
4	Distance bike (miles)
5	Time walk (min)
6	Distance walk (miles)

Transit Skims

Transit skims are generated for peak (PK) and off-peak (OK) periods and six path types (bus, project mode, pnr-bus, pnr-project, knr-bus, and knr-project). It must be noted that even though skims are generated for PNR and KNR path types, DaySim only used walk access skims. It automatically determines the PNR/KNR station for a drive transit trip and obtains the skim value for the drive portion from highway skims files. The files can be found in Master\{{SCENARIO_DIR}\Output\DaySim\ - PK_WalkBus.TXT, PK_WalkCR.TXT, OK_WalkBus.TXT, and OK_WalkCR.TXT. It should also be noted that for now, project mode is considered to be commuter rail (CR). Columns in the transit skims files are shown in Table 4‑3.

TABLE 4-3 TRANSIT SKIM FILE FORMAT

Column #	Name
1	Origin TAZ
2	Destination TAZ
3	In-Vehicle Time (min)
4	Initial Wait Time (min)
5	Transfer Wait Time (min)
6	Fare (cents)
7	Number of boardings