tru-traffic.com

Greg,

I was “ volunteered" to make a presentation on Tru Traffic TSPP-D to a group of NCDOT Engineers. They are attempting to identify a method to measure performance of arterials and develop a set of metrics to grade the arterial. The question was asked if Tru Traffic TSPP-D could satisfy this goal.

Some questions come to mind that I do not have answers for:

1 – Is there a software limit on the length of an arterial that can be set up with Tru Traffic TSPP-D? We are talking about crossing three counties on I-40, maybe 30+ miles between begin and end points.

2 – If the arterial can be set up (Interstate Route) would the GPS points be taken on the outside shoulders, one in each direction?

3 – If you were collecting the trip log over a long distance would you do it as a loop, from start point back to start point, or would you do it in two separate runs, start point to end point and back from end point to start point?

4 – For graphical presentation is there an easy method to fill in the area beneath the trip log line?

5 – I assume it would be possible to also set up intermediate points where there are interchanges or other system roads crossing over or under the study route. My basis for this assumption is the use of a “dummy” intersection where speed limits change along our signalized arterial timing projects. Is there a software limit as to the number of these “dummy” intersections?

6 – Is there a Tru Traffic TSPP-D report that can summarize incremental performance, such as between mileposts along the study corridor, and also provide a corridor summary average performance measure?

Thank you in advance for any constructive suggestions in response to these questions.


Sincerely,

W. C. "Will" Garner, Jr., PE
North Carolina Department of Transportation
Mobility and Safety Division
750 N. Greenfield Parkway
1561 Mail Service Center
Raleigh, NC 27699-1561

Fine questions, Will.

1. There is no explicit limit on either the length of an artery or the number of nodes along an artery. The implicit limits are the amount of available memory (which for typical systems probably limits the number of nodes to somewhere in the hundreds of thousands or millions), and the range of a 4-byte floating point number (which allows distances of billions of earth circumferences). The two beltways around Houston were studied this way a few years ago using Tru-Traffic (then called TS/PP-Draft) without any reported problems. One of the beltways is about 88 miles around and has about 130 nodes of interest (e.g., exit points and other crossings). The analysts just used defaults for the pseudo timings, since they only things that mattered to them were the node IDs, the travel distances between nodes, the geographic locations of the nodes, and the design speed.
   
   
2. Yes, the geographic points would be taken on the outside shoulders, one in each direction, assuming you want to consider both directions of travel with a single arterial diagram. If prefer to use two arterial diagrams, one for each direction of travel, then you may want drop one geographic point off the left shoulder and another off the right shoulder. This would allow you to use a different set of nodes for the two directions of travel.
   
   
3. It's largely a personal preference whether you record all your runs in a single trip log, or whether you stop & restart the recording between runs to make separate trip logs. The advantage of putting all runs in one trip log is that it can simplify bookkeeping. It lumps associated runs together, keeps your list of trip logs fairly small, and if you need to copy runs to a different file, you can copy them all with just the one trip log. The software will recognize the multiple runs in the trip log and include each one of them in either the TT&D report or the plots. The advantage of putting individual runs in separate trip logs is that you can then decide which runs to include in a plot or a TT&D report -- otherwise it's all runs or nothing. To copy all runs to a different file, you can highlight all the trip logs before copying them collectively to the clipboard. Note that even if you record all your runs in a single trip log, you may later split that trip log into individual runs. Do this in the Details Table for the trip log by selecting the point where you want to split the trip log then clicking the button Split Trip Log. The selected point will appear in both "halves" of the newly split trip log -- the before half and the after half.
   
   
4. With ver. 8.0, you may specify both the color and the thickness of the line tracing a given trip log to better call attention to it.
   
   
5. There is no explicit limit on either the number of these dummy intersections. As in item 1 above, the implicit limit on typical systems is probably in the hundreds of thousands or millions.
   
   
6. Yes, the TT&D report can summarize performance incrementally along the respective links, and it can provide a corridor summary average performance measure. See the user-defined report columns CumulativeAvgSpeedLOS_mph.URC and CumulativeAvgSpeedLOS_kph.URC, donated by Mark Taylor of Utah DOT, on the Downloads page http://www.tru-traffic.com/downloads.htm for examples of this very thing.

That's good team spirit, volunteering to make that presentation.

Regards.
Greg