Case Study 2 New York State Route 146 Corridor

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Case Study 2 New York State Route 146 Corridor
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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

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After Working Through this Case Study You Should
be able to

• 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.

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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
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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)
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• 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?
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What Analyses to Perform

• It is necessary to examine each intersection in
  each time period
• Also some specialized analyses (heavier-than-typic
  al traffic conditions)
• You might also want to do a system-level analysis
  to ensure that you have accounted for all the
  impacts that arise

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What Analyses to Perform
What other analyses might be necessary?

• For this TIA, how many intersection-level
  analyses will be involved?

Study the freeway interchange at 7 locations (see
HCMAG), equaling 84 more analyses
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
Instead of conducting all 168 analyses, were
going to focus on specific problems that let us
illustrate how to use the HCM
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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

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
What are some tools that should be used for this
case study and why?
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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)

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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

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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.
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Maxwell Drive Base Case Phasing
What other data do we need for this analysis?
2040 sec 812 sec 1018 sec
(skipped ½ time)

• The cycle length ranges from 30-70 seconds
  averages 48 seconds

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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

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Maxwell Dr Base Case Analysis
Base case results for signal timings that
equalize the delays for the critical movements in
each phase
What are the movement specific delays?
What are the average queue lengths for each
approach?
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Arrival Type Changes

• What are the effects of changing the arrival
  type?

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)
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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?
It could be a lot or a little.
In this case, are there any significant
differences?
No, the differences are minor
How can you study the impacts of potential
differences?
With sensitivity analyses.
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Skipped Phases
What combinations are possible with this
configuration?
Since the HCM doesnt 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
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Skipped Phases
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
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Sub-Problem 1b Maxwell Drive PM Peak Hour
With-Site Conditions
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

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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

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Critical Movement Technique
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
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Critical Movement Technique
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?
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Operational vs Planning Analyses
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.
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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?
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Conclusions
Current Configuration

• We found that the intersections geometry will
  have to change substantially.
• We needed a new NB approach and weve 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).
• Weve 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

Best Solution