Editing Intersection Extents

[SWAMike]

Hi there,

Could you please direct me how I can manually override the extents of intersection? I am modeling an interchange and I need some of the extents to be smaller than what Tru-Traffic is generating.

Thanks!

[bullock]

The extent of the intersection is determined by the greater of the following:

1. the number of lanes times the lane width, for each approach,
2. the extent or envelope of the measurements or GPS readings entered for the geographic coordinates of the intersection.
   
   Starting with ver. 11 (not yet released, as of this writing), that list has a few more items
3. the Minimum Extent specified in the user Preferences,
4. the Minimum Extent specified as a Network Parameter,
5. the Minimum Extent specified as an Arterial Diagram Parameter.

To reduce the extent, you may need to reduce one or more of these. You may need to declare fewer lanes or narrower lanes. If you have more than one geographic point assigned to the intersection (as recommended), then you may need to move them closer to the center of the intersection. Use Google Earth for that.

The extent rarely needs to be smaller. I'd be most interested to see your file, if you don't mind posting it here (or emailing it to me, if posting isn't an option), so I can learn more about what kind of problems an extent too large can cause. I may be able to offer more useful comments.

[SWAMike]

Sure.

The purpose of this file will be to determine the travel time & delay of a particular interchange. Only two of the points are actually intersections, the others are points of interest along the interchange. During data collection, the travel path was a loop around the interchange, so the initial and final points are very close to one another.

With this file, I have one very very large extent and a few others that need to be made smaller to avoid data overlapping. Personally, I have only used Tru-Traffic to generate Travel Time & Delay reports and I thought editing the extents of the intersection used to be a feature in a past version of the program.

[bullock]

The one very very large extent indeed needs to be fixed -- not because it's too large, but because it's wrong. All of the geographic points assigned to that node belong properly to the other points of interest along the route, and they're separately misassigned to the Gunston Rd and Martha Curtis Dr node. This not only makes for a large extent, but (worse) it also moves the node to the west side of the loop, while the true intersection of Gunston Rd and Martha Curtis Dr is at the east side.

While I recommend that you use Google Earth to correct that, you should first take a couple of preparatory steps to simplify the editing:

1. In the Intersection Parameters for Gunston Rd and Martha Curtis Dr, click the Coordinates... button and delete all but one of the geographic points in the list. I don't think it matters which one, as they're all wrong. Just leave one so we have something to edit once we get to Google Earth.
2. Click OK to return to the Intersection Parameters, declining the offer to reset the travel distance.
3. Change the ID Number from 0 to 1 (or to any other positive number that you may prefer).
4. After clicking OK, you'll need to acknowledge some warnings and decline a few offers to correct things, but there's one offer you want to accept: Noting that you've changed the ID Number and that the downstream nodes don't have ID Number specified yet, the software will offer to set all the ID Number downstream by incrementing this one's ID Number. Click Yes, and increment them by 1 (or by any other increment value that you prefer).
5. Now use Edit: Copy: Geographic Coordinates: Geographic Coordinates as Google KML to copy and paste the network coordinates into Google Earth.
6. Move the yellow pin for the Gunston Rd and Martha Curtis Dr node (#1) to the correct location.
7. Under My Places, copy the folder Shirlington Interchange Tru Traffic.kml to the clipboard.
8. Back in Tru-Traffic, paste into, say, the Network View.
9. The software should assign the geographic points to the correct nodes by matching the ID numbers.
10. Click the radio button to Replace (not Merge) the existing points with the newly pasted ones.

I have not checked the current, declared travel distances to have any opinion on whether you should let Tru-Traffic recaculate those for you yet.

The other points of interest along the route that have overlapping extents should all be fine the way they are. No need to correct anything there. While your runs go through both the entry point and the exit point as they're entering the loop, the software knows that the exit point is not a neighboring node of the entry point along the route, so it will disregard the spurious crossing.

[SWAMike]

Great!

Thank you for the guidance.