Have you ever wanted to construct your TMODEL network directly from an AutoCad drawing? Or have you wanted to edit a Traffic Analysis Zone (TAZ) Map after it was exported from ArcInfo? If you have already converted these files into TMODEL layer files, there are tools built into TMODEL that help you accomplish these tasks fast.

First, you must know the parameters of the file you are working with. Is there a specific color layer that you want to extract? Typically each color represents a separate attribute. For example, blue for water, yellow for rail, red for freeways, etc.

If you want to use option 4.4.9.16) EXPORT LAYER FILE TO NETWORK you must first consider the size of the file that will be created. How many points are there? Keep in mind that a separate node will be created for each point and a separate link will be used to connect them. You may want to eliminate some of the redundant or closely spaced points before exporting the layer file to a network. The operation of eliminating some of the unneeded points may even be helpful in reducing the size of your layer file so it draws faster on the screen.

You can extract the color you want from a complex layer file and eliminate extra points in one step. This feature is available in option 4.4.9.10) EXTRACT ONE COLOR LAYER TO NEW FILE. This option will read an existing binary layer (.LYR) file and write out a new layer file containing only those lines of a color selected by the user. It will also reduce the number of lines to match the minimum specified length.

All lines in the layer file that are less than the specified minimum length will be merged with the adjacent line, if they share the same common connecting node. You may wish to experiment with minimum lengths for lines. A line will only be merged with an adjacent line once during this operation. Therefore, if you have a large number of short connected lines, you may want to process it several times through this filter before using it. Keep each iteration and then determine which gives you the degree of detail compared with the speed of drawing that you desire. The number of lines can be determined by dividing the number of bytes in the layer file by ten (10).

This is a useful way for quickly deriving a TMODEL network from an existing drawing. It also gives you an alternate way of editing your layer files.

Another tool that we use when we are in the calibration zone is the LOS module (section 1.7.5). Using this module during the calibration of a model can give a user yet another way of looking at the reasonability of model operations. Inconsistencies can become very visually apparent by the various LOS color stratifications because LOS uses both the model link and node run data such as volumes, operating speeds (including intersection delay), and link density. In fact, we won't claim a model is validated until it is reviewed with the LOS module. Also, it is helpful in the review of future year forecasts to ensure the model is working right for the right reasons.

Tip from: Meher P. Malakapalli, Earth Tech; Bellevue, WA When you create a model and are calibrating, use the Willumsen's method to determine the external-external trip table (.TTI). It is a very efficient and useful method. The Willumsen's method needs a link file with existing counts, a node file, a starting trip table, and any other files you may be using for your model such as turn penalties, link/node delays etc. The starting trip table could be one that is made with a normal gravity model run, or a trip table with some arbitrary number of trips between each zone to each zone. Usually, if you do not have trip table produced by Gravity model, just add 100 trips or so between each zone to each zone. The Willumsen's method will create a trip table based on the exiting counts. To create an external trip table, just multiply all trips between all zones except to and from the externals by zero. This is your final external-external trip table. the external-internal and internal-external trips can then be easily found out by subtracting X-X origins/destinations from the total external volume.

I have used the Willumsen's method for this purpose my times and each time, it produced results that improved my model by 30-50%. In one case, I even used it to verify my origin-destination survey, and found out that if you have good actual counts, Willumsen's estimates are very reasonable and is probably the best available method.

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