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MHN Coding
Several domains are coded into the MHN to specifically control for the node attributes.
Node IDs in the MHN are restricted to <= 29999 (as nodes >= 30000 are reserved for the MRN).
Of the node IDs in the MHN, 1-3632 are special nodes which refer to zone centroids. 3633-3649 refer to point-of-entries (POEs).
(From the travel model appendix) "Trip generation zones (or subzones) are the smallest level of geography used in the travel demand model. Subzones are quarter-section-sized geographies that CMAP uses for household and employment forecasting." There are 17418 subzones. A subzone of 0 means that there is no corresponding subzone for that node.
There are 3649 modeling zones. 1-3632 are part of the CMAP region, while 3633-3649 are POEs (corresponding to the node IDs). The modeling zones were built by aggregating the subzones. A zone of 9999 means that there is no corresponding zone for that node.
The capacity zones were also built by aggregating the subzones.
| Code | Description |
|---|---|
| 0 | Unassigned |
| 1 | Chicago CBD |
| 2 | Chicago central area |
| 3 | Chicago |
| 4 | Inner-ring suburbs |
| 5 | Chicago urbanized area (IL) |
| 6 | Chicago urbanized area (IN) |
| 7 | Other urbanized area (IL) |
| 8 | Other urbanized area (IN) |
| 9 | Rural CMAP region |
| 10 | Rural Lake County (IN) |
| 11 | External area |
| 99 | Point of entry |
While physically, a road does not change throughout the day, the attributes of a road (such as the toll) might vary depending on the time-of-day (TOD). The MHN is set up so that the attributes are flexible enough to accommodate those variations.
| TOD | Description |
|---|---|
| 1 | Overnight: 8 PM - 6 AM |
| 2 | AM start shoulder: 6 AM - 7 AM |
| 3 | AM peak: 7 AM - 9 AM |
| 4 | AM end shoulder: 9 AM - 10 AM |
| 5 | Midday: 10 AM - 2 PM |
| 6 | PM start shoulder: 2 PM - 4 PM |
| 7 | PM peak: 4 PM - 6 PM |
| 8 | PM end shoulder: 6 PM - 8 PM |
Several domains are coded into the MHN to specifically control for the link attributes. A few of these domains are expounded on below.
The facility type determines the volume displacement function.
| Code | Description |
|---|---|
| 1 | Arterial |
| 2 | Freeway (controlled-access) |
| 3 | Freeway-Arterial Ramp |
| 4 | Expressway (limited-access) |
| 5 | Freeway-Freeway Ramp |
| 6 | Centroid Connector |
| 7 | Toll Plaza |
| 8 | Metered Ramp |
Centroid connectors are a special kind of link connecting the zone centroids to the highway network. They do not physically exist.
Toll plazas indicate a fixed-cost toll. Otherwise the toll is distance-based.
Some roads are only open during a certain part of the day.
| Code | Description | Open |
|---|---|---|
| 0 | N/A | |
| 1 | Unrestricted | 12345678 |
| 2 | AM Only | 2345 |
| 3 | PM Only | 1678 |
| 4 | Off-Peak Only | 15 |
| 5 | Peak/Shoulder | 234678 |
The field "MODES" is a 3-digit code. It's a combination of the mode (1-digit) and the truck restriction (2-digit). It describes what kind of vehicles are allowed on the link.
| Code | Description | Allowed |
|---|---|---|
| 0 | N/A | |
| 100 | All vehicles | ASHThmlb |
| 2XX | All vehicles + truck restrictions | Varies |
| 300 | Trucks only | AThmlb |
| 400 | Transit only (only called for transit networks) | None |
| 500 | HOV only | AH |
The mode 2XX indicates that there is a truck restriction applied by XX. A truck restriction of 0 (code 200) indicates that the truck restriction is unknown. Otherwise, codes vary from 1-49. To see their meanings you can just look in the geodatabase because I will not be typing it all out.
Also, I cannot believe I need a table for this table but:
| Mode | Description |
|---|---|
| A | Primary auto |
| S | Single occupant auto (SOV) |
| H | High occupancy (HOV) |
| T | General truck |
| b | B-plate truck |
| l | Light truck |
| m | Medium truck |
| h | Heavy truck |