Other Demand Models - bellevuewa/BKRCast GitHub Wiki
The BKRCast model includes the following supplemental models:
Truck Model
The truck model defines a truck based on relative weight classes and separates light, medium, and heavy trucks for analysis purposes. The following general categories of trucks are used in the BKRCast model:
- Light commercial trucks
- Four or more tires, two axles, and less than 16,000 lbs. gross vehicle weight (this also includes nonpersonal use of cars and vans)
- Medium trucks
- Single unit, six or more tires, two to four axles and 16,000 to 52,000 lbs. gross vehicle weight
- Heavy trucks
- Double or triple unit, combinations, five or more axles, and greater than 52,000 lbs. gross vehicle weight
The socioeconomic data used in the truck model are largely consistent with the data used in the passenger model; however, the employment data in the truck model are stratified into more employment categories. The following employment categories are used in the truck model:
- Agriculture/Forestry/Fishing
- Mining
- Construction
- Manufacturing (Products and Equipment)
- Transportation/Communication/Utilities
- Wholesale
- Retail
- FIRES (Finance Insurance Real Estate and Service)
- Education and Government
Trip Generation
Truck trip production and attraction rates are developed by truck type and industry.
Truck Trip Production Rates
| Employment Category | Heavy | Medium | Light |
|---|---|---|---|
| Agriculture/Forestry/Fishing | 0.2366 | 0.0889 | 0.4102 |
| Mining | 0.3405 | 0.0889 | 0.4102 |
| Construction | 0.0856 | 0.0998 | 0.4102 |
| Manufacturing (Products) | 0.2661 | 0.0858 | 0.3466 |
| Manufacturing (Equipment) | 0.0953 | 0.0858 | 0.3466 |
| TCU | 0.1075 | 0.2079 | 0.3466 |
| Wholesale | 0.1337 | 0.2552 | 0.3466 |
| Retail Trade | 0.0463 | 0.1637 | 0.3281 |
| FIRES | 0.0044 | 0.0434 | 0.1615 |
| Education and Government | 0.0068 | 0.0297 | 0. 1615 |
| Households | 0.0031 | 0.0358 | 0.0928 |
Truck Trip Attraction Rates
| Employment Category | Heavy | Medium | Light |
|---|---|---|---|
| Agriculture/Forestry/Fishing | 0.0988 | 0.2831 | 1.3161 |
| Mining | 5.0897 | 14.8073 | 47.9052 |
| Construction | 0.0290 | 0.0876 | 0.2585 |
| Manufacturing (Products and Equipment) | 0.0208 | 0.0538 | 0.2581 |
| TCU | 0.0378 | 0.0998 | 0.5082 |
| Wholesale | 0.0087 | 0.0352 | 0.1464 |
| Retail Trade | 0.0032 | 0.0123 | 0.0501 |
| FIRES | 0.0088 | 0.0375 | 0.1591 |
| Education and Government | 0.0073 | 0.0160 | 0.0966 |
| Households | 0.0071 | 0.0385 | 0.1732 |
Separate truck trips are added for three special generators.
Daily Truck Trips for Special Generators
| Area | Light | Medium | Heavy |
|---|---|---|---|
| SR 167 Warehouses | 320 | 460 | 990 |
| Port of Seattle | - | - | 5,890 |
| Port of Tacoma | - | - | 1,960 |
Trip rates for trucks are based on several data sources, including both local and national data. Due to the variability of data availability locally, and the strong differences between truck travel by region, a set of regional adjustment factors were calculated for truck production and attraction rates.
Truck Trip Adjustment Factors
| Area | Light | Medium | Heavy |
|---|---|---|---|
| Productions | 0.554 | 0.309 | 0.413 |
| Attractions | 0.749 | 0.500 | 1.375 |
Trip Distribution
The distribution of truck trips relies upon an exponential friction factor for trip distribution. The skims utilized in truck trip distribution are the bidirectional generalized cost and distance skims for trucks. The bidirectional skims are calculated using the AM and transposed PM peak-period skims from the assignment and skimming process. The following table lists the parameters used in truck trip distribution.
| Truck Type | Alpha | Beta | Impedance |
|---|---|---|---|
| Light | 0 | -0.04585 | AM/PM Cost/Dist |
| Medium | 0 | -0.0053 | AM/PM Cost/Dist |
| Heavy | 0 | -0.00001 | AM/PM Cost/Dist |
External Demand
External demand can be categorized into three types:
- Internal-external (II)
- External-internal (EI)
- External-external (EE)
Of the three categories, DaySim estimates only II and EI demand. EE trips for the 18 external stations around the BKRCast model region (coded as TAZs 1511 to 1528) are provided as input to the model system. The EE trips are developed based on the latest set of 2010 average weekday traffic counts from the Washington State Department of Transportation. The input EE trips by external stations can be found here.
Special Generators
Special generators are used in the model to account for locations that are not captured by standard trip generation inputs and rates. There are currently four special generators in the model system:
- SeaTac Airport (TAZ 1356)
- Tacoma Dome (TAZ 1357)
- Seattle Center (TAZ 1358)
- Exhibition Center (TAZ 1359)
SeaTac Airport special generator trips are split as 75% home-based other and 25% non-home-based-work to other trips. The other three special generators are added to the home-based other trip purpose. These special generators are added to the overall attractions for the respective trip purpose and are included before trip balancing occurs. The effect of the special generators is not an increase in overall trips but instead a redistribution in the number of attractions to these four zones. This is attributable to the fact that non-home-based and home-based-other trips are balanced to productions.
Group Quarters
Trip generation rates are developed for three noninstitutional group quarters:
- College Dormitories
- Military Quarters
- Retirement Homes
The following table shows group quarters trip generation rates per person by trip purpose and group quarter type:
Group Quarters Trip Rates (per Person)
| Trip Purpose | College Dormitories | Military Quarters | Retirement Homes |
|---|---|---|---|
| Home-Based Work | - | 0.37 | 0.10 |
| Home-Based College | 1.18 | - | - |
| Home-Based School | - | - | 0.03 |
| Home-Based Shop | 0.40 | 0.74 | 0.70 |
| Home-Based Other | 1.24 | 1.09 | 1.49 |
| Non-Home-Based | 1.00 | 0.76 | 1.04 |
| Total | 3.82 | 2.97 | 3.37 |
Refer to page 33 of PSRC 4K Model Documentation for more information about how these trip rates are developed.