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STEAM Frequently Asked Questions

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  1. I want to use the travel times from my traffic assignment rather than using travel times that STEAM generates. With STEAM, you can use speeds from your travel demand model's traffic assignments to calculate user benefits. From "Edit/Market Sectors", select "Use Input Network Speeds". This overrides STEAM's speed function and tells STEAM to use the speeds in the network file's free-flow speed field to calculate travel times between each destination pair.

  2. Can I supply STEAM with a travel time matrix from my travel demand model to calculate user benefits for highway users and avoid using the network analysis altogether? Yes. In the "Network and Trip Table File Name" window, leave the "run base network analysis" and the "run improvement network analysis" blank. Check the "ignore travel time analysis" box. Navigate to "other changes files" from the window pane on the left. Check the "employ in-vehicle travel time changes" box and select an input travel time file that has been formatted for use by STEAM (origin-destination-value format).

  3. I have a TransCAD highway network. How do I develop a highway network for STEAM? Building a highway network from TransCAD is a little different than building a highway network from other travel demand modeling software platforms. Most packages require separate records be created for travel in the A-B and B-A link directions. But TransCAD uses a direction code (dir code) to denote the permitted directions of travel: 0 for 2-way, 1 for A-B direction travel only and -1 for B-A direction travel only. You will need to write GIS/DK code to create separate records for 2-way links or, after you've output your network (including the direction code) into a format suitable for further data manipulation, you will need to write a macro or program to perform the task. Remember to sort the highway network on the A node.

  4. I am working with an auto market and a truck market. How does STEAM generate user benefits for truck-restricted highway networks? Right now, you need to create a separate set of build and no-build highway networks for each market. If there are network links that only trucks can use, then the links should only appear in the truck market's highway networks. Conversely, links on which trucks are prohibited would appear in the auto network but not in the truck network.

  5. What is the entry for average occupancy for? STEAM uses person hours of travel to calculate travel time benefits and vehicle miles of travel to calculate safety benefits. STEAM converts the person trip input files to vehicle trips for this purpose.

  6. What is the P/A to O/D conversion factor for? In the conventional four-step travel demand modeling process, home-based trips are expressed in what is called "production/attraction" (PA) format, before being converted to "origin/destination" (O/D) format. Home-based P/A tables typically contain two daily trips for each trip-maker, both of which originate at the production zone. These trips represent the trip from home to the attraction (e.g., work, school) and the return trip. When daily trips are in P/A format, the trip maker's zone of residence is easy to identify. When daily trips are in O/D format, it is difficult to distinguish between trips made by residents and those made by non-residents. The conversion factor allows STEAM to analyze benefits to residents and also to conduct its analysis at the O/D level. If you choose to use this feature, you should use the same conversion factor that your travel demand model uses.

  7. Do I need to run a network analysis every time I change the input parameters? No, you can reuse the network analysis from a previous STEAM session, as long as your build and no-build networks haven't changed.

  8. I'm evaluating a project that opens in the year 2010, but I only have highway networks for 2030. Can I just use my year 2030 results? It's always preferable to have a set of demands and highway networks which correspond to the actual year that your project begins to accrue benefits. If your analysis period begins in the year 2010 and you treat the project as though it begins accruing benefits in 2030, then you are missing 20 years worth of benefits.

    However, STEAM doesn't perform multiple-year analyses that would allow you to estimate total benefits over the life of an investment directly. STEAM performs a single year analysis, and discounts costs to the mid-point of the construction year.

    If you are performing a single-year analysis, it's not appropriate to use year 2030 results as a direct surrogate for year 2010 results. You will overstate the benefits, because the difference in benefits between the build and no-build in 2010 is likely to be lower than the benefits of the same project built in the year 2030.

    If you must use a year 2030 analysis to estimate benefits for a project that will open to traffic before 2030, you need to make sure that project costs are properly inflated to the year 2030. Then benefits and costs will have been aligned for a 2030 analysis, not 2010.



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