Freight Sensitivity. TREDIS is unique in its sophisticated treatment of freight, as it calculates how economic impacts within each region vary by industry -- depending on the mix of affected freight flows (commodities) and travel modes (truck, rail, air, water), and the extent to which they represent imports, exports or local freight movements. This feature is important for three reasons:

(1) It shows how economic impacts and benefits can differ depending on the nature of the affected modes and their passenger/freight mix.

(2) It can use local freight flow information on differences in the mix of commodities associated with alternative routes, corridors or transportation facilities.

(3) It provides results useful for freight planning, and also supports the freight benefit-cost analysis, which differentiates shipper benefits from travel cost impacts.

Default Option. Many highway studies have information about the mix of cars and trucks, but no information about the types of products being carried on the trucks. Similarly, many studies of rail and airport facilities have information about the volume or weight of freight being carried, but limited information on the mix of commodities being carried.

For all of those cases, the system assumes that there is a general pattern of commodity flows for each study region, which is calculated on the basis of the region's economic structure. The TREDIS Economic Adjustment Module is used to estimate the extent to which a study region's industry patterns generate freight flows for locally-used products, products brought in from suppliers located outside the study area, and locally-produced products that are delivered to customers in outside areas. For each type of product being shipped, the modal split (between truck, rail, air and marine transport) may be specified in scenario specifications. If not, then it is assumed to reflect average patterns as shown in the USDOT Freight Analysis Framework and the US BEA Transportation Satellite Accounts. Additional elements of in-flows and out-flows of freight are estimated using input-output and absorption byproduct matrices from IMPLAN.  The allocation of benefits among commodities (and associated industries) is assumed to occur in the same proportions as the study region's overall pattern of commodity flows. For studies where freight flow is not the dominant issue, such assumptions are generally considered to be reasonable.

User-Supplied Detail. Alternatively, there are studies where freight flow is a critical issue of interest. For those cases, TREDIS can be applied to make full use of waybill data, Global Insight Transearch data or locally-available survey data.  This approach is applicable for freight planning studies, where typically there is information about differences in freight mode mix and commodity mix among various corridors and facilities. Freight flow is also a concern for some studies of specific travel corridors, where the mix of affected commodities and industries may be different from general region-wide patterns. Finally, freight flow details can be important for cases where corridor alignment and/or project design options can lead to shifts in the mix of affected industries.

For all of these cases, TREDIS allows users the option of user-supplied detail - i.e., custom commodity flow data for their region(s). This information is used to determine which industries benefit from the cost savings that may result from transportation projects affecting road, rail, air, and/or water freight travel. Figures 1 and 2 show the layout of the optional TREDIS input pages for user-supplied details about commodity flow mix for affected scenarios.

In Figure 1, users can enter global inputs regarding the average value of commodities (by mode), as well as information describing time sensitivity. Both are used in translating changes in VHT into direct economic impacts across commodity categories. The time sensitivity factor allows for additional resolution among commodity codes, recognizing that certain late shipments can have a very high cost resulting from spoilage, logistical disruption, or retail timing.

Figure 1. Establishing the local value of commodity flows by mode, as well as differences in time sensitivity.

In Figure 2, users specify the modal commodity mix for each scenario and region being studied.

Figure 2. Specifying the detailed commodity mix.

In Figure 3, TREDIS provides supplemental information describing your study area's trade patterns. These include:
• domestic exports (locally-produced goods flowing to customers in the rest of the US),
• international exports (locally-produced goods flowing to customers outside of the US),
• industry imports (goods produced outside the region that flow to the region for local use), and
• household goods (commodities flowing to household customers).

Figure 3. Supplemental Report: Regional Trade Patterns

 TREDIS applications for freight studies include statewide studies in Massachusetts, Wisconsin and Maine, and regional studies for the Houston, Chicago and Vancouver (BC) areas.