The Forum is our bulletin board for discussion of TREDIS uses and features for economic impact, benefit-cost and policy analysis. Online posting of new items is temporarily suspended. Many important questions are answered below, and we continue to accept questions, answers and discussion threads. Anyone who wishes to add a question, answer or comment may do so by sending your text via email to This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Economic Impact Analysis Using TREDIS

• Study area size (willt47) -- How does size of the study area affect the economic impact measurement? Doesn't it bias the results?
• RE: Study area size (edr01) -- The area selected does affect impact measurement, but it is NOT a bias. In general, expanding the scale and breadth of a study area will tend to increase the gross economic impact. That occurs for several reasons. First, it increases the portion of affected travel movements (trips) that are "locally-based" -- i.e., having a local origin or destination and hence a direct effect on households or businesses. Second, it expands the observed economic "multiplier" effect -- i.e., the indirect impact on suppliers to affected businesses, and the induced impact from consumer respending of worker income. On the other hand, expanding the study area to be overly large will tend to make some of the business attraction moves appear to be just relocations within the same area. Each of these different effects is fully captured and measured within the TREDIS framework.
• Personal travel time (JMM) -- When I put in time savings for personal trips, I see a benefit/cost impact as expected, but nothing appears in the economic growth impact. Aren't these two measures supposed to be consistent?
• RE: Personal travel time (glenw) -- There is a reason for this difference. Having more free time has a value to people (which shows up in the B/C analysis), but it does not directly affect the flow of money in the economy. For business travel, on the other hand, savings labor time typically means saving money for the business, so that does affect money flow and thus leads to economic development (growth) impacts. TREDIS keeps this difference clean and apparent.

• Inflation Effect on Impacts and Benefits (JMM) -- Is there any way to recognize the fact that construction costs are rising faster than the rate of inflation? Doesn’t this affect benefit/cost analysis results?
• RE: Inflation Effect on Impacts and Benefits (edr01) Yes. While the benefit/cost analysis already controls for inflation, it is true that construction costs have been growing even faster than general inflation, and transportation building costs are rising yet faster due to growth of non-construction factors (land acquisition, context-sensitive design, etc.). That increases the net benefit of accelerated investment and decreases the benefit of delayed investment. In version 3, TREDIS includes a new feature that now allows the user to make adjustment for this factor.
• Construction spending - no benefit? (JMM) -- Tried using TREDIS. We added construction spending and see an economic impact but no benefit. Is something wrong?
• RE: construction spending - no benefit? (glenw) -- Nothing is wrong. Construction spending does increase the flow of income in the regional economy during construction years and TREDIS shows that impact. However, from a benefit-cost viewpoint, construction spending reflects a cost rather than a net benefit. (Another way of viewing it is to see that the money spent on construction occurs by foregoing other uses of that money which would also flow through the economy.)
• Modal Shift (SMorris) -- Our long-range urban transportation plan invests in transit to shift people out of cars, yet the input to TREDIS then shows a loss of auto vehicle trips that is larger than the gain in bus vehicle trips. That leads to a loss of total vehicle trips. Does that introduce error in the benefit calculation?
• RE: Modal Shift (edr02) -- In analyzing mode shift policies, it is important to distinguish changes in the pattern of person-trips and the pattern of vehicle-trips.

• Environment and safety (mwilliams) -- How do environmental and safety benefits get measured and used in the benefit-cost calculation?
• RE: environment and safety (edr02) -- TREDIS provides options for users to estimate accident, injury and fatality impacts, as well as air quality or other environmental impacts, based on changes in vehicle-miles of travel. Alternatively, it also provides an option for users to do their own external calculations of environmental impact and just enter those calculated results. All of these impacts can be considered in the benefit-cost calculation (though they do not all affect the separate calc of regional income growth).

• Access and Collaboration (rodt) -- We want open access and collaboration among users within our state DOT, but we want to allow consultant use of TREDIS restricted to a single project. Is there a way to accomplish this?
• RE: Access and Collaboration (balsadt) -- Yes. When you add users in the initial setup, there are options to control viewing and copying access. That allows any one user to enable others in their same account to view only the projects or scenarios that they want to share. It also requires others seeing those datasets to rename them before using them, so that no one can accidentally overwrite anyone else's work.
• Construction Cost (USR11) -- I have a construction schedule that is staged with different levels over time, yet TREDIS appears to allocate the construction cost equally over the construction period. Can this be overridden? Is there a way to make use of my construction schedule?
• RE: Construction Cost (balstadt) -- In TREDIS version 3.3, users can input a custom construction schedule on the project page. After you have defined your project (set up regions and time periods), and after you have fixed your construction period, click the green "Spending Allocation" button. This will bring up a table where you can enter, for each year in the construction period, the fraction of total construction budget spend in that year. Note that the sum over all years should equal 1. This information is later used to estimate total construction impacts on a year-by-year basis.

• Intermodal facilities (RGL) -- Can you add listings of the names of the airports and intermodal terminals that are being used for measuring access times?
• RE: intermodal facilities (balstadt) -- Yes. These are being added to "Supplemental Report B" next to the appropriate access value. Now active for v3.3
• National impacts (rbrown) -- I'd like to see more detail differentiating local vs national benefits and costs.
• RE: National impacts (tredis team) -- Actually, this feature is scheduled to be added in the next release
• Risk-Uncertainty (donw) How about adding risk/uncertainty in the cost benefit analysis?
• RE: Risk-Uncertainty (tredis team) -- We'll work on adding this feature in the future
• Mode choices (SMorris) -- Please make it possible for us to adjust the mode labels so that we can distinguish commuter rail, intercity rail and rail transit as alternatives.
• RE: Mode choices (tredis team) -- You can already redefine available mode-purpose slots to represent alternative variants of those modes. However, the ability to freely and fully change the mode and purpose labels and features will be added in a future release