ID# C206001

Problem 6: Route 146 Arterial Study 

Printable VersionProblem 6 Printable Version

So far, we’ve looked only at individual intersections. We’ve ignored the way in which the intersections interact and the challenge of finding a way to coordinate the signals.

Exhibit 2-1. Route 146 in Clifton Park

This problem speaks to that issue. We’re going to look at seven intersections simultaneously: the Shenendehowa Campus entrance, Moe Road, Maxwell Drive, Clifton Country Road, the I-87 Interchange, Fire Road (the signalized intersection on the east side of the interchange, Intersection F) and Route 9 (Intersection G) simultaneously. Refer to Exhibit 2-1 to become familiar with the intersection locations.

[ Back ] [ Continue ] to Analysis Plans

 
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ID# C2060A1

Problem 6: Route 146 Arterial Study

Analysis Plans
 During our analysis, we will focus on the PM peak. We’ve studied that timeframe at each of the intersections within the case study. Moreover, we’ll focus on the PM With condition since it has the most traffic. The intersecting counts and signal timings we’ve obtained will be used as basic inputs to create a TRANSYT7-F (Version 9.5) simulation dataset. We’re using TRANSYT7-F because, for signalized networks, it is an analysis tool that is in common use today. However, it should be emphasized that TRANSYT7-F is being used in this case study for illustrative purposes only, and other programs are available that would serve our purposes equally well.

We will exercise TRANSYT7-F in simulation mode to see how it thinks the network is performing. Finally, the analysis software will optimize the performance of the network as a coordinated system to see the optimal signal timings should be.

with Analysis
 
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ID# C2060A2

Problem 6: Route 146 Arterial Study

Analysis
Our first challenge is to create the TRANSYT-7F input dataset. We’re not going to describe all the details of how to do that here, but we will provide a short description of what’s involved. Dataset 79 is the actual dataset we created.

First, you will need to specify the lane arrangements at the various intersections. Here’s what we decided was appropriate. The abbreviations should be easy to read, and the numbers in parentheses, where they appear, imply more than one lane:

bullet

Shen Entrance: EBT, EBR, WBL, WBTR, NBL, NBTR, SBLTR

bullet

Moe Road: EBL, EBTR(2), WBL, WBTR(2), NBL, NBR, SBLTR

bullet

Maxwell Drive: EBL, EBTR(2), WBL, WBTR(2), NBL, NBT, NBR, SBL, SBT, SBR

bullet

Clifton Country Road: EBL, EBT(3),EBR,WBL(2),WBT(2),WBR,NBL(2),NBT,NBR, SBL(2),SBTR

bullet

I-87: EBT(2), EBR, WBT, WBR, NBR, SBR

bullet

Fire Road: EBL, EBT(2), WBTR(2), NBLT(2), NBR(2), SBL, SBR

bullet

Route 9: EBL(2), EBT(2), EBR, WBL, WBTR, NBL(2), NBTR(2), SBL, SBT(2), SBR

You can revisit the Exhibit 2-2 (the Route 146 aerial photograph) to see if you agree with these decisions. For the first four intersections, you can also review the HCM input datasets. For the I-87 interchange, we only needed to model the westbound-to-northbound entry ramp, westbound-to-southbound left turn onto the southbound entry ramp, the southbound-to-westbound exit ramp, the eastbound-to-southbound entry ramp, and the southbound-to-eastbound exit ramp to capture the impacts of traffic enteLevel of Servicend leaving the system. (If you know TRANSYT-7F, you’ll realize that you can’t model these flows accurately just with the mid-block entry option.) The geometry of the Fire Road intersection was presented in Exhibit 2-48. Exhibit 2-64 contains the configuration of the Route 146 and Route 9 intersection.

Exhibit 2-65. Route 146 Network Volumes - PM With Conditions

  with Problem 6

 

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Exhibit 2-65.  Route 146 Network Volumes - PM With Condition

 

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ID# C2060A3

Problem 6: Route 146 Arterial Study

The PM Existing and PM Without volumes used in the analysis are shown in Exhibit 2-65. There are unsignalized side streets in the network, such as Bruno Road, Tallowood Drive, and the Municipal Plaza, but the traffic volumes on these roads are not substantial. You’ll also see the tangential network involving Old NYS 146, Park Avenue, and Plank Road that we’ve decided to omit from the present analysis. You could argue that at least the extension of Clifton Country Road north across Old NYS 146 and Park Avenue should be included because there are times when the queue at Route 146 does back up across the Old NYS 146 intersection. In this analysis we haven’t done that.

The other information we had to specify included:

bullet

saturation flow rates for each of the lane groups in the bullet list above

bullet

volumes for each of the lane groups

bullet

signal timing plans (these are consistent with the HCM input datasets)

bullet

distances between the intersections

bullet

link-to-link relationships for the way in which the flows cascade through the network from upstream intersections to downstream intersections

bulletminimum phase lengths
bullet

opposing links for the permitted lefts and the right turns that can move when there is no competing traffic, as at Clifton Country Road northbound

to Findings

 

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ID# C2060F1

Problem 6: Route 146 Arterial Study

Findings

Our first run involved simulating the network using the signal timings developed in the HCM analyses. Complete datasets for the two main runs we performed are available for T7F1 and T7F2 signal timings. The output datasets for each of these runs are in Dataset 81 and Dataset 82, respectively. Except for Maxwell Drive, the timings we developed in the HCM were adequate. Exhibit 2-68 shows a comparison among three sets of timings for the network. The first are the timings we obtained from the HCM analysis. The second are timings we hand-generated in TRANSYT7-F to get acceptable v/c ratios for all of the lane groups. The third are the timings developed by TRANSYT-7F when it optimized coordinated operation across the network.

Exhibit 2-68. Route 146 Network Signal Timings from Three Sources

Phase

Shen

Moe

Maxwell

CCR

Fire Road

Route 9

HCM

T7F1

T7F2

HCM

T7F1

T7F2

HCM

T7F1

T7F2

HCM

T7F1

T7F2

HCM

T7F1

T7F2

HCM

T7F1

T7F2

1

29

31

77

4

4

5

4

10

16

6

6

5

-

41

60

-

23

16

2

7

7

5

22

22

77

29

28

46

14

14

15

-

14

3

-

36

19

3

10

8

16

14

14

16

11

21

28

27

27

31

-

26

30

-

39

22

4

20

21

-

-

-

-

5

2

6

18

18

18

-

3

3

-

5

7

5

-

-

-

-

-

-

-

-

-

20

20

21

-

-

-

-

26

15

6

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

-

22

15
T7F1: Hand-adjustment to HCM results, uncoordinated simulation
T7F2: T7F-9 optimal timings at 110-second cycle length

As you can see, at the Shen entrance, we didn’t need to adjust the signal timings very much to get acceptable performance from TRANSYT-7F at that intersection. The same is true at Moe Road and Clifton Country Road. Only at Maxwell Drive, and only for Phases 1 and 3 (the left-turn phases), that we needed to adjust the signal timings (substantially) in TRANSYT-7F to get acceptable v/c ratios.

The third green times (T7F2) are the values developed by TRANSYT-7F in optimizing the coordinated performance of the network. To give you a sense of the performance improvement provided with the T7F1 signal timings, the network had 300 vehicle-hours of delay (out of 455 total vehicle-hours of travel), while in the optimized scenario (T7F2), there were 282 vehicle-hours of delay (8% less) out of 436 vehicle hours of travel. The original signal timings were already fairly well matched to the traffic flows.

One important point to note about the analysis pertains to the westbound-to-southbound left turn at the I-87 interchange. We specifically included the I-87 interchange as a node in the network so we could look at the performance of this movement. In the T7F1 run, this movement had a degree of saturation of 145%, well above the 95% that TRANSYT-7F sets as an upper limit. We saw this as a significant problem and determined that some action would have to be taken to mitigate the long delays that occur there.

It is interesting to note that in the T7F2 solution, that problem has been rectified. TRANSYT-7F found a way to coordinate the signals at Clifton Country Road and Fire Road so the left turn can have a degree of saturation equal to 101%. This is not as good as the 95% that’s desirable, but it is much better than the 145% we had in the first case.

 to Discussion

 

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ID# C2060D1

Problem 6: Route 146 Arterial Study 

Discussion
There are several important points to make based on this problem. The first is that HCM analyses prepared us quite well for the network analysis. TRANSYT-7F was able to improve the performance of the system (delay-wise) by only about 8%, when it optimized the signal timings. In terms of assessing the performance of these intersections, we learned a lot from the HCM analyses that helped prepare us for the TRANSYT-7F investigation.

The second observation is that the way the HCM treats these intersections is very similar to the way they are treated in TRANSYT-7F. The two analytical methods expect very similar inputs, treat the problem in similar ways, and produce similar outputs. If you review the Help screens and text in TRANSYT-7F, you will find numerous references to the HCM. This indicates a significant consistency between these two tools, providing some assurance that findings obtained from the HCM will be similar to those from TRANSYT-7F, and vice versa.

The one major difference between the HCM and TRANSYT-7F is that the capacities of the saturation flow rates are derived by the HCM, whereas they are inputs in the case of TRANSYT-7F. Oftentimes, it helps to do the HCM analyses first and get credible saturation flow rates for the various lane groups before starting a TRANSYT-7F analysis. That will increase the consistency of the results you obtain.

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