Problem 4: Clifton Country Rd/Route 146 Intersection
Base Case Phasing and Volumes
Analysis Plans Description of Analyses
Overarching Issues 4a: AM peak hour -
Existing Conditions 4b: PM peak hour -
Existing Conditions 4c: 2004 PM - With vs
Without Conditions
The main question at this intersection will be: are geometric changes and/or adjustments in signal timing needed to accommodate the site-generated traffic?
Characteristics of the Clifton Country Rd intersection
Fully actuated signaling
EB approach is 5 lanes wide (left, triple through & signalized right)
WB approach is 5 lanes wide (double left, double through & free right)
SB approach has 3 lanes (left, left/through, & right/through)
NB approach has 4 (double left, through & free right)
2 large shopping complexes on each side of intersection
Major interchange with I-87 ~1/10 mile east of intersection
Observations?
Highest volumes on
EB & WB approaches
High volumes in the PM Peak
Sub-problem 4a: Clifton Country Road AM peak hour - Existing Conditions
AM existing conditions will be used to examine:
Lane utilization Coordination Lane group definitions
Lane Utilization
L T R Tot L T R Tot L T R Tot L T R Tot
Delay 34.5 28.6 10.2 25.6 31.3 21.0 12.9 23.4 33.1 32.0 33.2 33.0 32.3 32.0 25.9
v/c 0.0 0.8 0.2 - 0.5 0.7 - - 0.4 0.2 0.3 - 0.4 - -
95-Queue 0.2 15.6 5.3 - 6.9 20.0 - - 4.4 2.2 3.2 - 4.4 - -
Queue 0.1 8.3 2.6 - 3.5 11.0 - - 2.1 1.1 1.6 - 2.2 - -
Delay 34.5 22.5 10.2 20.5 30.9 19.6 12.9 22.4 33.2 32.0 33.2 33.0 32.3 32.0 23.4
v/c 0.0 0.6 0.2 - 0.5 0.7 - - 0.4 0.2 0.3 - 0.4 - -
95-Queue 0.2 13.1 5.3 - 6.9 19.1 - - 4.4 2.2 3.2 - 4.4 - -
Queue 0.1 6.8 2.6 - 3.4 10.4 - - 2.2 1.1 1.6 - 2.2 - -
1.0 0.7 1.0 - 0.9 0.9 1.0 - 1.0 1.0 1.0 - 1.0 -
Exhibit 2-40. Clifton Country Road Effects of Lane Utilization
Condition*Performance
Measure
Eastbound Westbound Northbound SouthboundOA
31.2
0.2
2.5
1.2
Observed Lane Utilization 1.0
Dataset 33 No Lane Utilization
31.2
0.2
2.5
1.2
Dataset 32 Base Case
The EB through is the movement where it is most important to use the real lane utilization
Why is that?
The real lane utilization is so different from the HCM default
Coordination
L T R Tot L T R Tot L T R Tot L T R Tot
Delay 34.5 28.6 10.2 25.6 31.3 21.0 12.9 23.4 33.1 32.0 33.2 33.0 32.3 32.0 25.9
v/c ratio 0.0 0.8 0.2 - 0.5 0.7 - - 0.4 0.2 0.3 - 0.4 - -
95-Queue 0.2 15.6 5.3 - 6.9 20.0 - - 4.4 2.2 3.2 - 4.4 - -
Queue 0.1 8.3 2.6 - 3.5 11.0 - - 2.1 1.1 1.6 - 2.2 - -
Delay 34.5 20.1 2.4 17.2 31.3 21.0 12.9 23.4 33.1 32.0 33.2 33.0 32.3 32.0 22.6
v/c ratio 0.0 0.8 0.2 - 0.5 0.7 - - 0.4 0.2 0.3 - 0.4 - -
95-Queue 0.2 14.2 1.7 - 6.9 20.0 - - 4.4 2.2 3.2 - 4.4 - -
Queue 0.1 7.5 0.8 - 3.5 11.0 - - 2.1 1.1 1.6 - 2.2 - -
Delay 34.5 37.1 18.0 33.9 31.3 21.0 12.9 23.4 33.1 32.0 33.2 33.0 32.3 32.0 29.1
v/c ratio 0.0 0.8 0.2 - 0.5 0.7 - - 0.4 0.2 0.3 - 0.4 - -
95-Queue 0.2 16.5 8.1 - 6.9 20.0 - - 4.4 2.2 3.2 - 4.4 - -
Queue 0.1 8.8 4.1 - 3.5 11.0 - - 2.1 1.1 1.6 - 2.2 - -
Exhibit 2-41. Clifton Country Road Impacts of Coordination on the Eastbound Approach
Condition*Performance
Measure
Eastbound Westbound Northbound SouthboundOA
Dataset 32 Base Case
31.2
0.2
2.5
1.2
Dataset 34 Arrival Type 5 EB
TH&RT
31.2
0.2
2.5
1.2
Dataset 35 Arrival Type 1 EB
TH&RT
31.2
0.2
2.5
1.2
What are the effects of changing the Arrival Type from 3 to 5?
Reduction in EB delays and queue length
What if we assume the coordination is worse than random arrivals?
Significant increase in delay, which also means longer queues
Lane Group Definitions
The HCM is capable of analyzing many different lane groupings: exclusive lefts (one, two, three, etc.
lanes) shared left-and-through lanes through lanes shared right-and-through lanes exclusive rights
But it cannot do lane-by-lane analyses, and there are some lane groups that it doesn’t accommodate easily
Lane Group Definitions
The southbound approach has the following lane configuration: left, left/through through/right
The HCM doesn’t provide for an exclusive left-turn lane in conjunction with a left/through lane.
So what do you do?
Two criteria must be satisfied: 1) the innermost lane gets as much use as the center lane and the outermost lane gets very little use. 2) the queue lengths on the innermost lane and center lane are about balanced.
Based on the analysis this approach seems to be consistent with field observations
Sub-problem 4b: Clifton Country Road PM peak hour - Existing Conditions
PM existing conditions will be used to examine:
Lost time Demand vs. Volume Right turns on red
Lost Time
Start-up lost time is the initial green time that is not effectively used due to the perception, reaction, and start-up times required by the lead vehicles.
What is the HCM default for lost time?
2 seconds
What is the extension of effective green time?
The number of seconds, after the yellow interval begins, that vehicles are still entering the intersection
What is the HCM default for the extension of effective green time?
2 seconds
What are the effects of having both values the same? Different?
Demand vs. Volume
Intersection turning counts yield volumes, whereas arrival counts yield demand
Congested intersections have demand/volume ratios > 1.0 during the peak hour.
What happens when the ratio becomes larger than 1.0?
Queues begin to form and grow when the demand to capacity (D/C) ratio is greater than 1.0. Queues begin to dissipate when the D/C ratio falls below 1.0.
Demand vs. Volume
L T R Tot L T R Tot L T R Tot L T R Tot
Delay 41.8 50.4 14 40.9 52.3 20.4 13.1 32.4 37.3 50.5 54.7 45.5 53.2 48.5 39.9
v/c ratio 0.4 0.97 0.45 - 0.92 0.69 - - 0.69 0.81 0.82 - 0.91 - -
95-Queue 1.8 20 11.4 - 16.7 18.9 - - 9 12.5 10.6 - 14.5 - -
Queue 0.9 10.9 5.9 - 9 10.3 - - 4.6 6.5 5.5 - 7.7 - -
Exhibit 2-43. Clifton Country Road PM Existing Base Case Conditions
Performance Measure
Eastbound Westbound Northbound SouthboundOA
Dataset 38 Base Case
84
35.7
0.6
8.9
4.5
ConditionCycle Length
What observations can be made for this intersection?
High delays and fairly high v/c ratios Near capacity
For the with-site condition, the D/C ratio should be checked; mitigation will probably be necessary if it exceeds 1.0
Right Turns on Red
L T R Tot L T R Tot L T R Tot L T R Tot
Delay 41.8 50.4 14 40.9 52.3 20.4 13.1 32.4 37.3 50.5 54.7 45.5 53.2 48.5 39.9
v/c ratio 0.4 0.97 0.45 - 0.92 0.69 - - 0.69 0.81 0.82 - 0.91 - -
95-Queue 1.8 20 11.4 - 16.7 18.9 - - 9 12.5 10.6 - 14.5 - -
Queue 0.9 10.9 5.9 - 9 10.3 - - 4.6 6.5 5.5 - 7.7 - -
Delay 41.8 50.4 14.5 40.3 52.3 20.4 16.3 30 37.3 50.5 79.7 52.7 53.2 48.5 39.7
v/c ratio 0.4 0.97 0.5 - 0.92 0.69 0.39 - 0.69 0.81 0.95 - 0.91 - -
95-Queue 1.8 20 13 - 16.7 18.9 9.1 - 9 12.5 13.9 - 14.5 - -
Queue 0.9 10.9 6.8 - 9 10.3 4.6 - 4.6 6.5 7.3 - 7.7 - -
Dataset 39 Downward
Adjusted RTOR85
35.7
0.6
8.9
4.5
Dataset 38 Base Case
84
35.7
0.6
8.9
4.5
Exhibit 2-44. Clifton Country Road PM Peak Hour Effects of RTOR
ConditionCycle Length
Performance Measure
Eastbound Westbound Northbound SouthboundOA
What observations can be made about right turns on red?
For the EB approach 10% of the right turning vehicles turn on red
For the WB approach all of them are expected to turn on red since there is a separate right-turn auxiliary lane & not much opposing traffic
For the NB approach we assume as many vehicles turn right during phases 1 & 2 as WB lefts in a single lane (550/2)
Sub-problem 4c: Clifton Country Road 2004 PM - With vs. Without Conditions
EB WB NB L T R Tot L T R Tot L T R Tot L T R Tot
Delay 49 55 16 45 56 21 14 34 42 57 60 51 62 56 44
v/c 0.5 1 0.5 - 0.9 0.7 - - 0.7 0.8 0.8 - 0.9 - -
95-Queue 2.1 23 13 - 19 21 - - 10 15 12 - 17 - -
Queue 1 13 6.9 - 10 12 - - 5.4 7.7 6.3 - 9.2 - -
Delay 51 54 17 51 65 26 15 40 50 61 64 56 67 61 50
v/c 0.4 1 0.5 - 1 0.8 - - 0.8 0.8 0.8 - 0.9 - -
95-Queue 2.5 28 16 - 21 27 - - 13 16 13 - 19 - -
Queue 1.2 16 8.6 - 12 16 - - 7 8.5 7 - 10 - -
Delay 52 56 17 53 68 26 15 41 53 62 66 58 70 63 51
v/c 0.4 1.1 0.5 - 1 0.8 - - 0.8 0.8 0.8 - 0.9 - -
95-Queue 2.6 29 17 - 22 29 - - 14 16 14 - 19 - -
Queue 1.3 17 8.9 - 12 16 - - 7.4 8.7 7.1 - 10 - -
Delay 48 33 7.7 27 48 28 17 35 46 52 55 49 49 47 37
v/c 0.4 0.9 0.6 - 0.9 0.8 - - 0.8 0.8 0.8 - 0.8 - -
95-Queue 2.4 22 9.5 - 19 28 - - 13 15 12 - 16 - -
Queue 1.2 12 4.9 - 10 16 - - 6.7 7.8 6.4 - 8.6 - -
Exhibit 2-46. Clifton Country Road Scenario Investigations-Without & With Site-Generated Traffic
ConditionsCycle
Length
RTOR Performance Measure
Eastbound Westbound Northbound SouthboundOA
Dataset 40 Without
95 39 267 340
40.6
0.63
10.5
5.4
Dataset 41 With Conditions Base
Case107 43 267 340
45.6
0.63
11.8
6.1
With Conditions 30% Higher Site
Traffic108 44 267 340
46.4
0.64
11.9
6.2
Dataset 43 With Conditions 30%
Higher Site Traffic-
enhanced
101 44 267 340
39.4
0.57
10.8
5.6
What has been done here? What can be done?
Observations?
Conclusions and Observations
This problem has explored a number of capacity modeling issues in the context of the Clifton Country Road intersection.
We examined time periods, the relationships among HCM methodologies, times to use other tools, and interpretation of results.
We examined lane groups and lost times.
We explored issues of queue spillback, feasibility of identified solutions, demand versus volume and right turns on red.
In the PM with-site condition, we focused on feedback the impacts of various assumptions about the future conditions and the tie between geometric changes and intersection performance.