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