Externals

External trip making in SoundCast consists of three distinct trip types:

• Trucks
• Work Trips
• Non-Work Trips

External trips are an input to SoundCast and are balanced to observed vehicle volumes across 18 external stations in the region. Traffic volumes at external stations are updated with each new base year and are obtained from the Washington State Department of Transportation. 80% of the total non-truck external trips are assumed to be SOV and the remaining are treated as shared ride trips. The total daily external vehicle trips in the 2014 base year are:

Total Daily External Truck Trips

TAZ	Location	Daily Count
3733	I-5 @ Thurston County	132,000
3734	SR-507	21,800
3735	SR-7	2,850
3736	Paradise Rd.	1,800
3737	SR-123	1100
3738	SR-410	1000
3739	I-90	33,800
3740	US 2	4,600
3741	Mountain Loop Hwy	90
3742	SR-530	2,100
3743	SR-9	1,500
3744	I-5 @ Skagit County	64,400
3745	Old Pacific Hwy	9,100
3746	SR-532	20,700
3747	Mukilteo-Clinton Ferry	6,050
3748	SR-104 (Hood Canal Br.)	17,600
3749	SR-3	18,400
3750	SR-302	4,200

External Truck Trips

Truck trips are based on a combination of observed truck counts where available and HPMS based truck percentages for lower volume screenlines where truck trips do not exist. External truck destinations continue to be based on the REEBIE truck flow data from the early 2000's. These destinations will be updated using currently available ATRI data in the near future. External truck trips account for approximately 28,000 of the daily external vehicle trips (9% of the total external trips).

Total Daily External Truck Trips

TAZ	Location	Daily Count
3733	I-5 @ Thurston County	11,800
3734	SR-507	1,000
3735	SR-7	200
3736	Paradise Rd.	200
3737	SR-123	0
3738	SR-410	0
3739	I-90	5,100
3740	US 2	200
3741	Mountain Loop Hwy	0
3742	SR-530	400
3743	SR-9	100
3744	I-5 @ Skagit County	5,000
3745	Old Pacific Hwy	800
3746	SR-532	700
3747	Mukilteo-Clinton Ferry	200
3748	SR-104 (Hood Canal Br.)	900
3749	SR-3	700
3750	SR-302	200

External Work Related Vehicle Trips

External work trips have been revised to use the US Census Longitudinal Employer-Household Dynamics (LEHD) datsets to assign external work trips to the region. These external work trips make up approximately 80% of the 330,000 daily vehicle trips that enter the region each and every day. These trips are a direct input to SoundCast and absorb a share of the jobs available in any given parcel. These distributions do not change into the future, but the level of external activity is grown based on forecasted employment growth in the region.

Total Daily External Work Vehicle Trips

TAZ	Location	Daily Count
3733	I-5 @ Thurston County	87,700
3734	SR-507	15,000
3735	SR-7	1,500
3736	Paradise Rd.	1,600
3737	SR-123	0
3738	SR-410	300
3739	I-90	19,300
3740	US 2	2,400
3741	Mountain Loop Hwy	0
3742	SR-530	1,000
3743	SR-9	1,000
3744	I-5 @ Skagit County	41,700
3745	Old Pacific Hwy	4,400
3746	SR-532	11,000
3747	Mukilteo-Clinton Ferry	5,200
3748	SR-104 (Hood Canal Br.)	11,200
3749	SR-3	13,400
3750	SR-302	2,700

In the code, these work-related trips are processed in the create_ixxi_work_trips script. This generates a trip table by mode (SOV, HOV2, HOV3, and time and day, which are assigned to the network in subsequent trips. The inputs for these trips are stored in the soundcast inputs database in the external_trip_distribution table.

Since we are adding travel for people outside the region to jobs located in the region, we need to account for the reduced number of jobs available for regional workers in the work location model of Daysim. Additionally, we need to update parameters for Daysim so workers that have jobs outside the region are removed from considering jobs within the region. This is handled by creating the parcel-level file psrc_worker_ixxifractions.dat, which is a Daysim input. In addition to these parameters, this process also accounts for military jobs (primarily at Joint Base Lewis-McChord) and removes most of the jobs from Daysim's work location process since these jobs are not open to the general public and are often held by military personnel living on base. In general, trips to/from the JBLM area are fixed and are made available along with the external_trip_distribution table. The JBLM zones are treated as external zones and are scaled to match a license-plate survey of trips between JBLM and PSRC zones.

External Non-Work Related Vehicle Trips

External non-work trips are calculated by subtracting the total truck and work trips from the observed external vehicle count. Non-work trips are then distributed using a gravity model formulation for non-work based trips.

Total Daily External Non-Work Vehicle Trips

TAZ	Location	Daily Count
3733	I-5 @ Thurston County	24,500
3734	SR-507	4,000
3735	SR-7	600
3736	Paradise Rd.	300
3737	SR-123	500
3738	SR-410	100
3739	I-90	4,600
3740	US 2	600
3741	Mountain Loop Hwy	100
3742	SR-530	100
3743	SR-9	900
3744	I-5 @ Skagit County	8,300
3745	Old Pacific Hwy	3,900
3746	SR-532	8,800
3747	Mukilteo-Clinton Ferry	600
3748	SR-104 (Hood Canal Br.)	4,200
3749	SR-3	2,700
3750	SR-302	1,200