Case Study 2 New York State Route 146 Corridor
This case study is about a Traffic Impact Assessment for a proposed site development in Clifton Park, New York
Problems focus on the chapters of the HCM dealing with:
interrupted flow facilities (especially signalized intersections)
arterials freeway interchanges arterial weaving
Analyze the operation of signalized & unsignalized intersections, and urban arterials using the HCM.
Understand what input data are required and the assumptions that are commonly made regarding default values for the HCM procedures for these facilities.
Know the appropriate kinds of analysis that should be undertaken for existing facilities, including the scope of the analysis.
Understand the limitations of the HCM procedures and when it is appropriate to use other models or computational tools.
Know how to reasonably interpret the results from an HCM analysis and how these results can be used to support a particular decision regarding a change to a transportation system.
After Working Through this Case Study You Should be able to:
Analytical tools
HCM Part II Facility type HCM Part III HCM Part IV Level of analysis
Problem type
HCM 10 15 28 Planning Functional
Design
Macroscopic simulation
11 16 29 Design Detailed design
Microscopic simulation
12 17 30Operational
analysis Access
management
Other tools 13 20Intersection operations
14 22Arterial
operations
23Network
operations
24Freeway
operations
25 Corridor study
18Sub-area
Study
19 Areawide study
Uninterrupted
Interrupted
The table shows ways to classify traffic analysis problems that are appropriate for analysis with the HCM, cells with blue text will be discussed in this case study
Characteristics of the Corridor
Multi-lane arterial Serves trips to &
from: 3 major shopping
centers a local school
district campus many commercial
& residential areas
What would be reasonable time periods to collect data?
- AM / PM peaks & peak of the traffic generator
- Possibly Saturday midday & the Friday peak hours (e.g. for a shopping center)
For this case study the goal is to mitigate negative impacts resulting from traffic related to the site & general background traffic growth.
Related to the goals and objectives are performance measures, including: Delay Level of service (LOS) Total vehicle hours of travel Total vehicle miles Air pollution outputs Noise impacts
What scenarios will we need to model to address these goals?
What other potential issues may need to be addressed as part of this development?
What Analyses to Perform
It is necessary to examine each intersection in each time period
Also some specialized analyses (heavier-than-typical traffic conditions)
You might also want to do a system-level analysis to ensure that you have accounted for all the impacts that arise
What Analyses to Perform
For this TIA, how many intersection-level analyses will be involved?
84 - 7 intersections: A through G
- 3 time periods: AM peak, PM peak, Weekend peak - 4 conditions: existing, future without site, future with site, future with mitigation
What other analyses might be necessary?
Study the freeway interchange at 7 locations (see HCMAG), equaling 84 more analyses
Instead of conducting all 168 analyses, we’re going to focus on specific problems that let us illustrate how to use the HCM
Tools to Use
It is important to select analysis tools that strike a balance between the amount of effort they require & the amount of insight they provide
What are some tools that should be used for this case study and why?
1 – Highway Capacity Manual: for all the intersection analyses and location-specific analyses at the freeway interchange
2 – Computerized arterial signal system optimization procedure: for arterial analysis of intersections A - D
Data
What types of input data are required? Facility-related information (e.g., number of
lanes, lane widths, lane configurations) Traffic-related information (e.g., vehicular &
pedestrian volumes for all conditions) Operational information (e.g., signal timings)
Problem 1: Maxwell Drive/Clifton Park Blvd Intersection (existing conditions and the with-site conditions analyses) 1a: PM Existing
Base Case Arrival Time Changes Sensitivity to Data Skipped Phases
1b: PM With-Site Conditions Analysis Configuration Issues HCM Planning Method Cycle Length Discussion Critical Movement Techniques Operational versus planning analyses Uncertainty
Maxwell Drive Characteristics
The Maxwell Drive / Route 146 intersection is signalized and fully actuated
To the east ~2,000 ft east is the intersection of Clifton Country Rd / Route 146
To the west ~4,000 ft is the intersection of Moe Rd / Route 146
To the north ~300 ft is the intersection of Park Ave / Maxwell Dr.
All three of these upstream intersections are signalized and fully actuated.
Maxwell Drive Base Case Phasing
20–40 sec 8–12 sec 10–18 sec
(skipped ~ ½ time)
The cycle length ranges from 30-70 seconds & averages 48 seconds
What other data do we need for this analysis?
Maxwell Dr – Base Case Analysis
Characteristics: Peak Hour: 5 – 6pm Intersecting vehicles = 2877 PHF = 0.94 for all approaches 7% trucks Arrival Types
2 for EB approach 3 for WB and SB
approaches
Maxwell Dr – Base Case Analysis
L T R Total L T R Total L T R Total
Delay 18.2 5.3 - 7.7 - 16.7 17.3 - 20.8 18.5 13.7
Queue 1.8 4.2 - - - - 2.4 - 2.7 - -
Exhibit 2-8. Maxwell Drive PM peak - Existing Conditions, Base Case ResultsEB
Arrival Type
Heavy Vehicles
Phase Skip
Signal Timing
Performance Measure
EB WB SB
OA
16.7
9.92 Yes Yes Base
Base case results for signal timings that equalize the delays for the critical movements in each phase
Observations?
What are the movement specific delays?
What are the average queue lengths for each approach?
Arrival Type Changes
What are the effects of changing the arrival type?
L T R Tot L T R Tot L T R Tot
Delay 18.2 5.3 - 7.7 - 16.7 17.3 - 20.8 18.5 13.7
Queue 1.8 4.2 - - - - 2.4 - 2.7 - -
Delay 11.9 3.5 - 5 - 16.7 17.3 - 20.8 18.5 12.7
Queue 1.3 2.9 - - - - 2.4 - 2.7 - -
Delay 2.2 0.6 - 0.9 - 16.7 17.3 - 20.8 18.5 11.2
Queue 0.5 0.8 - - - - 2.4 - 2.7 - -
Delay 27.2 8 - 11.5 - 16.7 17.3 - 20.8 18.5 15.1
Queue 2.3 5.2 - - - - 2.3 - 2.7 - -
Exhibit 2-9. Maxwell Drive Effects of Variations in the Eastbound Arrival Type
Data-set
EB Arrival Type
Heavy Vehicles
Phase Skip
Signal Timing
Performance Measure
EB WB SBOA
1 2 Yes Yes Base16.7
9.9
2 3 Yes Yes Base16.7
9.9
3 5 Yes Yes Base16.7
9.9
4 1 Yes Yes Base16.7
9.9
If the coordination gets worse (arrival type 1), the EB left-turn delay could increase to 27.2 sec (45% more than the base case)
Observations?
Data Sensitivity
If data were collected for the same time period at the same location on multiple days, what kind of variance would you expect?
LT TH Tot TH Tot LT RT Tot
Delay 18 5.3 7.7 17 17 17 21 19 14
Queue 1.8 4.2 - 9.9 - 2.4 2.7 - -
Delay 19 6 8 17 17 17 27 21 14
Queue 2 5.8 - 10 - 2.3 3.4 - -
Delay 19 6.1 7.9 17 17 16 19 17 13
Queue 1.9 6.1 - 10 - 1.4 2.3 - -
Exhibit 2-10. Maxwell Drive Comparative Results from Three Datasets
DatasetPerformance
Measure
EB WB SBOA
1
5
6
In this case, are there any significant differences?
How can you study the impacts of potential differences?
With sensitivity analyses.
Observations?
No, the differences are minor
It could be a lot or a little.
Skipped Phases
What combinations are possible with this configuration?
Since the HCM doesn’t ask for dual-ring phasing how should this phenomenon be modeled (min greens, max greens, gaps, etc.)
Adjust the modeled signal timings so that they reflect an average cycle given that specific phase(s) will sometimes be skipped
Skipped Phases
LT TH Tot TH RT Tot LT RT Tot
Delay 18 5.3 7.7 17 17 21 19 14
v/c 0.4 0.4 - - 0.6 0.6 - -
Queue 1.8 4.2 - - 2.4 2.7 - -
Delay 20 6 8.4 43 23 31 25 27
v/c 0.3 0.4 - - 0.7 0.7 - -
Queue 2 4.8 - - 2.9 3.3 - -
Delay 36 6.9 12 15 33 42 36 18
v/c 0.5 0.4 - - 0.7 0.8 - -
Queue 3 6.5 - - 4.3 4.9 - -
8 No Adjust
15.2
0.75
12.8
7 No Adjust
42.7
1.01
16
1 Yes Base
16.7
0.87
9.9
Exhibit 2-13. Maxwell Drive Effects of Skipped Phases
DatasetPhase Skip
Signal Timing
Performance Measure
EB WB SBOA
Do skipped phases make a difference?
YES!!!
Why is this delay 3 times greater for Dataset 7 than the base case?
The cycle length is 5 sec. longer
What happens if when the other phases are adjusted to reflect the change in the phase 2 timings?
The WB thru delay is less than the base case, but all of the other movements have more delay
Sub-Problem 1b: Maxwell Drive PM Peak Hour – With-Site Conditions
LT TH RT Tot LT TH RT Tot LT TH RT Tot LT TH RT Tot
PM Without 202 902 0 1,104 0 1,098 228 1,326 0 0 0 0 366 0 195 561 2,992
PM With 202 902 150 1,254 150 1,098 228 1,476 150 90 150 390 366 60 195 621 3,741
Exhibit 2-14. Maxwell Drive 2004 PM Peak Hour Volumes
2004 Conditions
Eastbound Westbound Northbound SouthboundTotal
Configuration Issues
What are some reasonable configurations for the new site?
What are some of the tools to develop a signal timing plan?
- HCM planning method for signalized intersections
- Critical lane analysis Observations?
HCM Planning Method
For the HCM Planning Method what needs to be supplied? Intersecting volumes Left-turn treatment
(protected, permissive, compound, etc.)
Number of lanes (left, through, and right)
Peak hour factor Min & max cycle lengths Coordination situation
(yes or no) If parking is present
What does the model determine? Lets us know if the
configuration will work
Reports the capacity condition (above capacity, at, nearly at, below, etc.)
Presents a phasing plan
Critical Movement Technique
LT TH RT LT TH RT LT TH RT LT TH RT
C-1 3 1 1 1 1 1 1 1 1 139.4
C-2 4 1 1 1 1 1 1 1 1 175.5
C-3 3 1 1 1 1 93.5
C-4 3 1 1 1 1 1 1 1 1 114.9
C-5 3 1 1 2 1 1 1 1 1 1 1 87.2
C-6 3 1 1 1 1 204.9
C-7 3 1 1 2 2 106.7
C-8 3 1 1 84.4
Exhibit 2-16. Maxwell Drive Critical Movement Analysis Results
2 2 3 3
1 1
2 2 1 1
2 2
2
2 2
2 2 2 2
2 2
2 2
ScenarioLost Time
(sec)
Number of Lanes
Cycle LengthEastbound Westbound Northbound Southbound
What are the differences between scenarios?
Different lane use plans produce very different cycle lengths (also very different phasing plans)
Combining certain movements, like the NB & SB rights and the EB & WB lefts, can get more productivity out of the intersection and reduce the cycle length
Critical Movement Technique
LT TH RT LT TH RT LT TH RT LT TH RT
C-1 3 1 1 1 1 1 1 1 1 139.4
C-2 4 1 1 1 1 1 1 1 1 175.5
C-3 3 1 1 1 1 93.5
C-4 3 1 1 1 1 1 1 1 1 114.9
C-5 3 1 1 2 1 1 1 1 1 1 1 87.2
C-6 3 1 1 1 1 204.9
C-7 3 1 1 2 2 106.7
C-8 3 1 1 84.4
Exhibit 2-16. Maxwell Drive Critical Movement Analysis Results
2 2 3 3
1 1
2 2 1 1
2 2
2
2 2
2 2 2 2
2 2
2 2
ScenarioLost Time
(sec)
Number of Lanes
Cycle LengthEastbound Westbound Northbound Southbound
Do you see any weaknesses in the critical movement analysis approach?
How do shared lanes complicate the situation?
What about intersections where there are no left-turn lanes?
Observations?
Operational vs Planning Analyses
LT TH RT Tot LT TH RT Tot LT TH RT Tot LT TH RT Tot
Delay 38.8 22.6 15.4 32.5 17.3 39.5 24.3 25.1 38 31 28.1 34.2 28.7
Queue 4.6 - 2.2 - 2.3 2 2.8 - 8 1.2 3.9 - -
Delay 63.4 32 23 42.6 19.5 38.6 21.2 38.2 37.9
Queue 6.5 - 3.1 - 1.4 - 3.6 - -
Delay 65 34.8 24.3 51.1 34.6 57.8 39.3 54.5 46.9
Queue 6.8 - 3.3 - 1.9 - 5.4 - -
Exhibit 2-17 Maxwell Drive Operational Analyses
ScenarioCycle Length
Performance Measure
EB WB NB SBOA
C-4 6519.5 34.4
10.3 17.6
C-7 9025.9 44.9 50.5 62.6
13.7 23 7.2 8.3
C-8 9329 54.2 72.3 76.4
15 25.8 8.7 9.4
What are the differences between scenarios?
We can make the signal work, in an operational analysis, for the conditions that the planning analyses suggested should work.
We have also seen that the cycle lengths are sometimes different.
Uncertainty Issues
For this intersection we will look at:
Base Case (C-4) Double Lefts, NB & SB (C-
7) Separate NB/SB phases
(C-8) 30% more site-generated
traffic (+30%) 30% less site generated
traffic (-30%)
Compare and contrast the different scenarios.
Which seems to have the least delay?
Delay Trends
0.0
20.0
40.0
60.0
80.0EL
ET
ER
WL
WT
WR
NL
NT
NR
SL
ST
SR
C-4
C-7
C-8
30%
-30%
Conclusions
We found that the intersection’s geometry will have to change substantially.
We needed a new NB approach and we’ve found it useful to reconfigure the SB approach.
Our best solution uses 3 lanes SB (left, through, and right) and 3 lanes NB (left, through, and right).
We’ve used the PM with-site condition to look at:
Changes in LOS due to the addition of the site-related traffic
The relationship between geometric improvements and LOS
Differences between planning and operational analyses
The role of uncertainty in affecting the results obtained
Current Configuration
Maxell Road
Route 146
N
Best Solution