How does Tru-Traffic deal with complicated intersections

[Mallikarjuna]

Hello Mr. Greg,

I have a couple of questions to ask. I discussed with my colleagues if they could find any tricks to resolve this problem. But, We really couldn't get around this problem. So I hope you might have some solutions.

First Question:
I have a simple signalized intersection with 4 approaches which is located in the middle of the arterial that we are working on. The arterial actually turns right (southbound) or turns left(Northbound) at this intersection. So when I want to enter timing plan for this intersection, the through movement is actually the right turn movement (Southbound) or left turn movement (Northbound). I can't use offset reference point at the start of the through movement. Instead I will have to use "start of right turn movement/left turn movement". But, I can't specify that in the software. How can I set the the offset reference point if I have a situation like this? If you think it is good idea for you to look at the intersection diagram, please let me know. I will send it to you.

Second question:
In intersection properties window and timing plan tab, why do we have two left turns for all approaches? and why don't we have right turns?. We have situations where the right turn is allowed only on green. How do we model that? .

Third question:

We have recently conducted a travel time and delay runs and got some trips from the study area. We have also got existing signal timing plans from Local DOT for all intersections in the corridor. We followed the procedure that you mentioned in the manual to synchronize the System clock to Signal clock. We did that before we start our trip logs. We have the current signal timing entered and the trip logs for the corridor we are working on. We see trip logs are still running through red band at certain intersections. I don't know whether to believe trip logs or timing plans. I think the trip logs are OK as we saw the signal lights turning green when we approach the location. But, the timing plan says it is supposed to be green. We also can't say the DOT has given us wrong timing plans. We made sure the offsets and timings are OK. So, what might be the cause for this problem?

Hope I am clear on my questions. Please let me know if something confusing you.

Thank you
-Arjun

[bullock]

Hi, Arjun.

First Question:
Yes, please. If you would send the intersection diagram, that will help focus my suggestions.

Second Question:
Tru-Traffic allows there to be two protected "cross-traffic" turning phases in the cycle. (These are left turns, in the Americas). You may specify this by setting the protected turning phase sequence to Lead+Lag to indicate that the turning phase both leads and lags the opposing through phase.

To specify a "with-traffic" turning phase (right turn, in the Americas) on the through green only, uncheck the RTOR (or LTOR in left-hand drive rule regions) box. At present, Tru-Traffic assumes protected with-traffic turning phases are simultaneous with the through phase -- it does not model protected with-traffic turning phases that extend outside the through phase.

Third Question:
The easiest way to check is while you're in the field with the GPS receiver tracking. Use either

• View: Cycle Timer or
• View: GPS View: Options: When tracking, mark on diagram Mark all positions at current time with a horizontal line

to view the cycle timer. Watch when the cycle timer crosses the phase transitions at each signal, comparing it to what you see in the field, to determine whether the offsets and splits are set correctly. If necessary, you may have to adjust the signal cycle start time on the GPS View: Clocks page. Be sure to allow for any variations in the splits due to traffic gapping out early. You can do these checks now, even after recording the trip logs. If necessary, you may override the signal cycle start time for the trip logs by either

• setting it in each trip log's properties or
• by setting it once in GPS View: Clocks page then selecting all the trip logs in the GPS View, right-clicking, and choosing Signal Cycle Start Time.

If, after confirming the timings, the trip logs still run through the red, then it's probably that the side-street gapped out early and the signal was actually green at the time on the diagram that you see the trip log crossing the intersection. If that doesn't seem to account for it, please send the .Dgm file to me. It might give me further ideas or we might determine there's a bug in the software.

For our mutual convenience, please try to use separate topics for questions not closely related.

Regards.
Greg

[Mallikarjuna]

Hello Greg,

Sorry for posting multi topics in a single question. I was little lazy. I have just sent you the intersection diagram. Please check your email.

Thank you
-Arjun

[bullock]

Thank you, Arjun. I received the intersection diagram.

For this case, I would fake the signal timings so the phases for movements along the artery, although they're turning movements, are entered as through splits, and the minor movements are entered as turning movements to/from the side-streets. Having done that, the offset and offset reference point may correct themselves automatically. You'll also want to add a note to the intersection parameters, and possibly an annotation to the arterial timings diagram, documenting what's been done. Although the timings window and the timings report will show tweaked values, the arterial timings diagram will appear correct in the sense that it will show green & red at the appropriate times for the through movements.

That may be enough for you to work out the details, but if you need additional help, then I'll need to know more about the timings: phase sequence, splits, offset, and offset reference point.

Regards.
Greg

[Mallikarjuna]

Hello Greg,

We have used the same trick to come with an answer. But we are not still completely convinced with it. Please see your email again, I have sent you an image of timing window that shows how I have set up the timing for this intersection.

The problem we have is the arterial northbound ( Hylan Blvd to steuben St, left to top in the diagram) has a protected left turn phase and the through will be a right turn if I consider left turn as through. Anyway, it will be much clear if I provide you the phasing sequence.

There are 3 phases: A, B and C , Cycle length 120 sec

A : Hylan Blvd through goes for 42 seconds

B : Steuben st through and Kensington Ave through goes for 36 secs

C: Left turn and through from Hylan Blvd to Steuben and right turn from Steuben St to Hylan Blvd goes for 42 secs.

Sequense is A->B ->C

Anyway I have also attached timing plan for this intersection with my email.

my question is left turns on main lines in timing window are actually not left turns from the main line. They are actually throughs from phase B. But Tru-Traffic is considering as left turns from main line and naming phase numbers as same as throughs. We actually do not want this to happen. One other thing is, 42 seconds of green shown in the timing window for cross streets is right for one approach that is for Phase A Hylan Blvd southbound. But it is wrong for other side, because it has 84 seconds of green overlaps between Phase A and Phase C. I can't have different green time for both approaches unless I select lead/lag options those are actually for turning movements not for through movement.

There are lots of things going on. Its pretty complicated for me to understand how the software can deal with this..

Thank you
-Arjun

[bullock]

Thank you, Arjun.

I received the timings/phasing diagram and screen shot. There may be considerations that I still don't understand, but it seems to me that, to get the arterial timings diagram to look correct, it's sufficient to set the protected turning phase sequence to None-None, and to set the arterial through split to 42 seconds (phase C). Everything else is considered side-street movements as far as Tru-Traffic is concerned -- a turn either to or from the side-street.

In effect, we're saying that the movements between W Hylan Blvd and Steuben, either direction, are the "through" movements, and everything else, being a conflicting movement, is some form of "side-street" movement and is lumped together as a virtual side-street. I'd probably use Lead-None for the side-street, with A being the protected turning phase and B being the through phase along the side-street, But it may be just as well to set the side-street to None-None and lumping A and B splits together for that. It mainly depends on whether you're planning to enter volumes and plot a platoon-progression diagram.

From the timings/phasing diagram that you sent, I don't understand which phase has the offset reference point. But from your initial question, I gather that its the start of phase C, so setting it to either Start of Arterial Green or Start of First Through Movement should suffice.

If this doesn't seem sufficient to you, please help me understand what I'm still missing.

Regards.
Greg

[Mallikarjuna]

Thank you Greg. I think we did the way you are suggesting. But, let me try changing lead/lag options and see if that helps. Yes, you are right, Phase C has been set as offset reference point since it has arterial through.

Since Tru-Traffic does not have direct solution, we will see how we can work around.

Thank you for your suggestions. I will continue this discussion if I have any doubts.

Thank you
-Arjun

[bullock]

Sounds good, Arjun.

I forgot to mention: Regarding the phase numbers, click the phase/movement buttons at the center of the Timings page to open a window where you can set the correct phase number for the given movement.

Regards.
Greg