cen 519 paper (cabral)

7/31/2019 CEN 519 Paper (Cabral)

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Table of Contents

I. Abstract ............................................................................................................................... 5

II. Background ......................................................................................................................... 6

III. Introduction ......................................................................................................................... 7

IV. Intersection Data ................................................................................................................. 9

i. Existing Traffic Volumes .................................................................................................... 9

ii. Signal Phases and Timing ................................................................................................. 11

iii. Accident Information ........................................................................................................ 13

V. Data Analysis .................................................................................................................... 14

i. Adequacy of Current Signal Phasing and Timing ............................................................ 14

ii. VISSIM Simulation of Existing Conditions ..................................................................... 16

VI. Alternatives ....................................................................................................................... 20

i. Proposed Alternatives to the North Attleborough BPW ................................................... 20

ii. New Proposal .................................................................................................................... 21

iii. VISSIM Simulation of Proposed Design .......................................................................... 26

VII. Discussion of Results ........................................................................................................ 28

VIII. Conclusions ....................................................................................................................... 29

IX. References ......................................................................................................................... 30

X. Appendix A ....................................................................................................................... 31

XI. Appendix B ....................................................................................................................... 34


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List of Tables and Figures

Table 1 - Peak Hourly AM Vehicle Volumes (4) ........................................................................... 9

Table 2 - Peak Hourly PM Vehicle Volumes (4) ............................................................................ 9

Table 3 - Signalized Intersection Approach Volumes .................................................................. 10

Table 4 - Signal Phasing and Timing Abbreviation Legend......................................................... 11

Table 5 - Loss Time Measurements (s) for the Route 1 NB Direction ......................................... 12

Table 6 - Loss Time and Saturation Headway .............................................................................. 13

Table 7 - Crash Report Totals from 2006-2008 (4) ...................................................................... 13

Table 8 - Calculated and Measured Critical Lane Flow and Capacity (vehicles per hour) .......... 15

Table 9 - Simulated Existing Mean Peak AM Delay Times, (s) ............................................... 19

Table 10 - Simulated Existing Mean Peak PM Delay Times, (s) .............................................. 19 Table 11 - Level of Service Delay Times for Signalized Intersections (11) ................................ 19

Table 12 - Cycle Length and Green Time Determination for Peak AM Volumes ....................... 24

Table 13 - Cycle Length and Green Time Determination for Peak PM Volumes ........................ 24

Table 14 - Peak AM Signal Phasing and Timing Sequence ......................................................... 25

Table 15 - Peak PM Signal Phasing and Timing Sequence .......................................................... 26

Table 16 - Simulated Proposed Design Mean Peak AM Delay Times, (s) ............................... 27

Table 17 - Simulated Proposed Design Mean Peak PM Delay Times, (s) ................................ 27

Table 18 - Comparing Peak AM Proposed vs Existing Delay Times........................................... 28

Table 19 - Comparing Peak AM Proposed vs Existing Delay Times........................................... 28

Figure 1 - Google Maps (6) Current Satellite Image of the Intersection (Zoom Out) .................... 7

Figure 2 - Google Maps (6) Current Satellite Image of the Intersection (Zoom In) ...................... 8

Figure 3 - Signalized Traffic Flow ................................................................................................ 10

Figure 4 - Startup Loss Times and Saturation Headway Determination ...................................... 12

Figure 5 - VISSIM Lane and Routing Decision Layout for Existing Conditions ........................ 17

Figure 6 - Route 1A Traffic Queuing for Existing Conditions ..................................................... 18

Figure 7 - Proposed Intersection Layout ....................................................................................... 22


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I. Abstract

This research investigates the traffic operations at the intersection of Route 1, Route 1A,

and Elmwood St in North Attleborough, MA. Route 1 and Route 1A run parallel to each other

and connect at the junction of Route 1 and Elmwood St, which forces vehicles to approach the

intersection from five directions. This awkward intersection has been responsible for high

accident rates and long queue lengths, especially during peak hours. The Town Board of Public

Works has addressed the need for improvements and has acquired traffic engineering

consultation from engineering firms in the area. The town has not yet made any decisions on the

future of the intersection due to the costly and complex proposals submitted. In this study,

VISSIM traffic simulation software from PTV Vision was used to simulate traffic flow for

existing peak AM and PM hours. The purpose of this report is to present the quantitative analysisof the current state of operations at the intersection, and propose an alternative in which the

VISSIM analysis of the simulation yields improved operations. The proposed alternative has

shown promise and will be provided to the North Attleborough Board of Public Works and the

employed engineering consulting firm. It is anticipated that this research will facilitate progress

on the improvement of operations at the intersection.

Keywords: Five-way signalized intersection, VISSIM analysis, North Attleborough Route 1


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II. Background

The Town of North Attleborough was established in 1694 along Old Post Road, which

provided the major transportation link along the east coast northward to Boston. As the center of

town expanded, Old Post Road through the downtown area was renamed to Main Street and is

known today as North Washington Street or Route 1A. Main Street intersected with local streets

at the northern end of town and formed a Y intersection. As transportation evolved from horse

drawn carriages to motorized vehicles, the volume of traffic through Main Street, which was the

main transportation link to Boston, resulted in severe downtown congestion. To alleviate the

congestion, a downtown bypass road was installed on the east side of downtown and runs

parallel to Main Street, which is now identified as Route 1 (2) . The newly constructed Route 1

became the main south to north thoroughfare which bypassed the downtown area, but created aunique intersection on the northerly section of town. The original Y intersection became an

X intersection with an intersecting local street on the east side, Elmwoo d Street (2) .

As the economies of the Boston and Providence areas expanded from the 1950s to today,

the traffic volumes and traffic speeds expanded significantly, yet the basic geometry of the

intersection is based upon the horse drawn carriage patterns of the 1800s and a bypass road of

1949 (2) . Growth in the region was further enhanced with the construction of Interstate 95 in the

1960s. The construction of I -95 and two interchanges in North Attleborough provided

opportunities for businesses and promoted residential growth. These factors further compounded

the traffic growth through an unusually shaped intersection which does not conform to current

highway design geometric standards (2) .


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III. Introduction

The intersection of Route 1, Route 1A, and Elmwood Street outside of the center of

North Attleborough has been a congested, problematic, and dangerous junction for drivers. This

intersection experiences high volumes of traffic for the businesses surrounding the area,

including a Dunkin Donuts at the merging southbound directions of Route 1 and Route 1A.

Elmwood Street consists primarily of residential properties, but controls access to the towns

largest recreation center, the Hockomock YMCA. Route 1A similarly holds hundreds of

residential properties, but also experiences high volumes of traffic for drivers commuting to the

center of town. Route 1 holds the heart of business for North Attleborough and surrounding cities

and is responsible for the majority of transportation through this intersection. Routes 1 and 1A

run parallel to one another and intersect at the junction of Route 1 and Elmwood Street. Thetraffic signals for the intersection direct traffic flow travelling through Route 1, but do not

control vehicles remaining along Route 1A at this location. The connection between these

roadways is one of the major factors for traffic queuing, delay times and frequent accidents. See

Figures 1 & 2.

Figure 1 Google Maps (6) Current Satellite Image of the Intersection (Zoom Out)


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Figure 2 Google Maps (6) Current Satellite Image of the Intersection (Zoom In)

The Town of North Attleborough has addressed the need for action to fix this

troublesome intersection. Their department of public works has been working to come up with a

plan to improve traffic flow in the area, but has not made any decision on how to proceed (5).

Beta Group, an engineering firm, has proposed several ways for the town to improve the

intersection, but negotiating these improvements have been challenging for several reasons. The

suggested solutions so far appear to be costly and complex, questioning how this project will be

funded and the state Departmen t of Transportations approval (5).

The purpose of this research is to quantitatively investigate the existing situation of the

intersection and seek out alternatives not yet proposed by Beta Group. Using VISSIM, a

microscopic multi-modal traffic flow simulation software (12) existing peak AM and PM traffic

volumes will be analyzed to examine the current quality of service. This software will also assist

in determining the effectiveness of proposed improvements by comparing the simulated resultsof any design changes to the existing conditions. The proposed solutions will be heavily

influenced by the restructured designs of other intersection improvement projects of similar

scenarios. All or any proposed improvements will follow the state intersection design guidelines

(8) before being subjected to the modeling software.


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IV. Intersection Data

The first step in analyzing the current state of the intersection of Route 1, Route 1A, and

Elmwood Street begins with data collection. Jason DeGray, P.E., of BETA Group (4) has

provided the existing peak AM and PM hourly traffic volumes as well as the signal phasing andcrash reports.

i. Existing Traffic Volumes

The traffic volumes presented in the study are the quantities of vehicles approaching and

leaving all 5 directions of this location. See Tables 1 & 2 for the 2010 peak hourly AM and PM

vehicle volumes, respectively.

Table 1 - Peak Hourly AM Vehicle Volumes (4)

ToFrom Route-1A NB Route-1 NB Elmwood St Route-1 SB Route-1A SB

Route-1A NB 20 60 160 260Route-1 NB 5 70 715 175Elmwood St 15 25 80 20Route-1 SB 60 230 20 5

Route-1A SB 170 85 0 5

Table 2 - Peak Hourly PM Vehicle Volumes (4)

ToFrom Route-1A NB Route-1 NB Elmwood St Route-1 SB Route-1A SB

Route-1A NB 45 50 70 205Route-1 NB 10 75 380 120Elmwood St 80 80 30 25Route-1 SB 205 735 50 5

Route-1A SB 405 145 50 55

As stated previously, the signal only controls traffic flow for cars travelling throughRoute 1. Figure 3 shows the number of lanes and traffic directions of each lane through the

signalized intersection. The peak AM and PM quantities of vehicles approaching the signalized

intersection (combining the Route 1A NB and SB volumes) are displayed in Table 3, and will be

later used to identify if the signal can adequately handle these peak volumes.


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Figure 3 Signalized Traffic Flow

Table 3 Signalized Intersection Approach Volumes

Peak Flow ( vph )Approach AM PM

Route 1 NB 785 455Route 1 NB LT 180 130

Route 1 SB 295 945Route 1 SB LT 20 50

Elmwood St (WB) 140 215Route 1A (EB) 330 415


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ii. Signal Phases and Timing

The traffic signals at this intersection only control the vehicles travelling and crossing

through Route1. All vehicles remaining along Route 1A at this location are not controlled by the

traffic signals, but experience conflict points from the vehicles leaving and entering Route 1. Thetraffic signal times and phasing are provided in Table 3. Neglecting the small pedestrian volume,

the signal sequence consists of a 3 phase system with actuators on the east and west bound

directions of the intersection (Route 1A and Elmwood St, respectively). The cycle length,

without the pedestrian phase, is 88 seconds and follows the same sequence every cycle. The

legend for the abbreviations within Table 3 is provided in Table 4.

Table 3 Signal Phasing and Timing (4)

Table 4 - Signal Phasing and Timing Abbreviation Legend

Symbol Signal Symbol SignalGLA Green Left Arrow R RedYLA Yellow Left Arrow W Walk

G Green FDW Flash Don't Walk Y Yellow DW Don't Walk


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In order to determine important traffic parameters, there are several other timing

measurements that must be recorded. These measurements: startup loss time ( l1 ), clearance loss

time ( l2 ), total loss time ( t L ), and saturation headway ( h s ), are computed using a stop watch

program. The saturation headway ( h s ) was the horizontal asymptotic average time between

vehicles to cross the stop line. The startup loss time ( l1 ) was the sum of the time the first four

vehicles to cross the stop line minus 4 saturation headways. The clearance loss time ( l2 ) was the

time between the last vehicle in queue crossing the stop line and the next movement receiving a

green light. The total loss time ( t L ) equals the sum of l1 and l2. Four loss time measurements

were taken during a peak hour from the Route 1 North Bound direction for the first 8 vehicles in

the queue crossing the stop line. The values for determining the loss time parameters can be

found in Table 5 and Figure 4.

Table 5 Loss Time Measurements (s) for the Route 1 NB Direction

Measurement#

Vehicle # Crossing Stop Line Clearance Time(s)1 2 3 4 5 6 7 8

1 3.0 3.0 2.0 3.0 2.0 2.0 2.0 2.0 5.02 4.0 3.0 3.0 2.0 2.0 1.0 2.0 2.0 4.03 4.0 4.0 2.0 2.0 2.0 2.0 3.0 2.0 5.04 3.0 3.0 1.0 2.0 2.0 2.0 2.0 2.0 4.0

Figure 4 Startup Loss Times and Saturation Headway Determination

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

0 1 2 3 4 5 6 7 8

T i m e

( s e c o n

d s )

Vehicle # Crossing Stop Line

Loss Times & Saturation Headway

Measurement #1

Measurement #2

Measurement #3

Measurement #4


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From the previous Table and Figure, the approximate average values for startup loss

time ( l1 ), clearance loss time ( l2 ), total loss time ( t L ), and saturation headway ( h s ) can be

determined. See Table 6 for these parameters:

Table 6 Loss Time and Saturation HeadwayParameter Time (s)

l1 3.3l2 4.5tL 7.8hs 2.0

iii. Accident Information

The following table contains the crash totals from the MassDOT crash reports at theNorth Attleborough Route 1-Route 1A-Elmwood St Intersection from 2006 to 2008; provided by

DeGray (4) .

Table 7 - Crash Report Totals from 2006-2008 (4)

Year Number of Accidents Number of VehiclesInvolved in Accidents Injuries

2006 15 30 4

2007 16 31 42008 17 35 3Total 48 96 11


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= Total Loss Time (seconds)C = Cycle Length (second)

Vc = (1 / 2.0) (3600 3 phases (7.8)(3600/88)) = 1,321 vph

Capacity, ci Equation 3

Where,G, y, ar = Green, Yellow, and All Red Time for i approachC = Cycle Length (seconds)

= Saturation Headway (seconds / vehicle)

Route 1 NB( ) = 1,002 vph

Route 1 SB

( ) = 675 vph

Route 1A (EB) and Elmwood St

( ) = 470 vph

Table 8 Calculated and Measured Critical Lane Flow and Capacity (vehicles per hour)

Direction CalculatedMaximums

MeasuredCritical Lane-Flow AM PM

All Approaches 1,321 648 713 Approach Capacity

Route 1 NB 1,002 483 293Route 1 SB 675 158 498

Route 1A (EB) 470 165 208Elmwood St 470 140 215

Table 8, above, shows the calculated theoretical maximum values for critical lane-flow

and approach capacities. The measured values appear to be significantly smaller than the

calculated maximums because there are two lanes at each approach of the intersection, with the


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exception of Elmwood St. The additional lane alleviates half the volume of traffic and allows the

measured peak values to stay below the theoretical maximums. Since the critical lane flow and

capacities for all approaches exceed the measured critical volumes, the existing signal phasing is

adequate in handling the peak volumes of flow. This confirms that changing the phasing and

timing sequence of the traffic signals would not significantly fix the intersection.

ii. VISSIM Simulation of Existing Conditions

The simulation software was used to model the current conditions of the Route 1, Route

1A, and Elmwood St Intersection. The existing signal phasing and timing sequence and peak

vehicle volumes (for AM and PM conditions) were input into the program to better understand

the present situation. Since the peak volumes were simulated using this software, the maximum

signal times were used for all approaches and the pavement detectors were neglected to simplify

programming of the model.

From the previous signal timing analysis, it is concluded that the existing sequence and

timing of the lights are adequate in handling traffic flowing through the intersection. The goal of

modeling the intersection using simulation software is to identify the problems that intersection

capacity and signal time equations fail to see. The first step was importing a Google Earth (4)

image of the intersection into the software, drawing travel lanes to scale of the dimensions of the

intersection. Figure 5 shows the VISSIM display of the intersection with blue centerlines for

travel lanes and pink lines for turning decisions.

Once the intersection was drawn out, the peak approach volumes were input for both AM

and PM conditions (2 individual simulations). Then, the percentages of the approach volumes

with their corresponding routing decisions (i.e. Elmwood St to Route 1 NB) were programmed

into the model followed by the given existing signal phasing and timing sequence. Numerous

other inputs were also input to account for roadway type, lane widths, vehicle acceptable

acceleration, simulation speed, etc. Once everything was input into the model, the simulationswere conducted. The vehicle types travelling through the simulated intersection were in default

percentages generated by the software and shown in random colors. The green, yellow, and red

lines at the perimeter of the intersection represent the traffic signal colors for each approach.


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Figure 5 VISSIM Lane and Routing Decision Layout for Existing Conditions

The simulations were conducted for both AM and PM volumes, and each showed similarproblems; the unregulated traffic flow on Route 1A causes long queuing. Vehicles trying to turn

from both northbound and southbound Route 1A to Route 1 created substantial queuing

problems. When vehicles at the front of the line for Route 1A were waiting for their signal to

turn green, vehicles travelling behind them are forced to wait for the Route 1A (EB) movement

to receive a green signal before they can advance even if they are staying on Route 1A. See

Figure 6 for a screen shot of the queuing problem described above.


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Figure 6 Route 1A Traffic Queuing for Existing Conditions

This queuing issue along Route 1A also causes backup on Route 1 for both northbound

and southbound approaches, when vehicles are trying to turn from Route 1 to Route 1A

southbound. Vehicles coming from Route 1A SB frequently block the box waiting for the Route

1A (EB) approach to receive a green signal and prevent traffic from flowing onto Route 1A. This

halt in traffic flow creates queuing on Route 1 which has the heaviest flow of traffic coming into

the intersection and subsequently causes long delay times. For both AM and PM peak conditions,

the simulation ran 5 times to acquire 85% confidence intervals of the mean delay times. See

Equation 4 for the determination of the confidence bounds following a normal distribution. From

these mean delay times, the current level of service can be determined for this intersection for

both peak AM and PM scenarios. See Tables 9 and 10 for the mean delay times and

corresponding levels of service from the simulation.

Equation 4

( ) (

)


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Where,

= Probability (85%)

= Mean Delay Time (s)

= Standard Deviation

= Number of Trials

1.44 = Z-value corresponding to 85% Probability

Table 9 - Simulated Existing Mean Peak AM Delay Times, (s)

ApproachMean (s) Standard Dev 85% Confidence Bounds

for Mean Delay (s) LOS Route 1 NB 6.0 0.6 5.6 6.4 ARoute 1 SB 3.1 0.7 2.6 3.5 A

Route 1A (EB) 71.0 10.9 64.0 78.0 EElmwood St 10.2 0.9 9.6 10.8 A - B

Table 10 - Simulated Existing Mean Peak PM Delay Times, (s)

Approach Mean (s) Standard Dev 85% Confidence Boundsfor Mean Delay (s) LOS Route 1 NB 3.4 0.6 3.0 3.8 ARoute 1 SB 64.1 16.3 53.6 74.6 D - E

Route 1A (EB) 104.1 18.1 92.4 115.8 F

Elmwood St 14.0 0.6 13.6 14.3 B

Table 11 Level of Service Delay Times for Signalized Intersections (11)

Level of Service

Delay(s/veh)

A 10 B 10 - 20C 20 - 35D 35 - 55E 55 - 80F 80

As shown in the Tables 9 and 10, the current quality of service of this intersection is not

optimal especially for the Route 1A approaches. Because of the high delay times during peak

traffic volumes, the town has sought out solutions to fix this intersection, which are discussed in

the following section.


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VI. Alternatives

As of February, 2012, BETA Group has delivered several possible alternatives to amend

this intersection. Three of these alternatives will be discussed and their design plans provided in

the following section. The town has yet to make any decisions for permanent solutions, but short

term improvements such as upgraded pavement markers and road signs have been suggested.

After analyzing these proposals submitted to the Board of Public Works, a new alternative was

discovered through this study.

i. Proposed Alternatives to the North Attleborough BPW

The three submitted alternatives discussed in this section are all viable solutions to

amending this intersection, but require eliminating traffic movements and or land acquisition.

The design plans for these three alternatives can be found in Appendix A. All of these solutions

have their pros and cons, which need to be weighed to determine the optimum solution.

The first concept, or Concept E, eliminates all traffic movements from Route 1A

southbound through the existing signalized intersection. Vehicles approaching from Route 1A

SB are given a straight only pavement marker, forcing drivers to maintain travel along Route 1A.

This movement elimination suggests that drivers may use the Dunkin Donuts parking lot as a

potential cut through for those whom need to get from Route 1A SB to Route 1 or Elmwood St.

Concept E shifts the sidewalks and curbing to allow for a Route 1SB right turn lane and Route

1A NB right turn lane onto Route 1 SB. This proposal also includes a second signal to be

installed at the Route 1-Route 1A merge to better regulate traffic flow. See Figure A1 in the

Appendix.

The second concept, Concept C-3, is very similar to the previous alternative, but requires

more construction and land acquisition. This concept eliminates the same movement from Route

1A southbound, but does not call for a signal to direct flow at that point. Route 1A NB will alsohave the separate right turn lane onto Route 1 SB, but the Route 1 SB added right turn lane to

Route 1A from the previous concept is not included. The major difference is the land acquisition

on the northern side of the intersection. The town would have to purchase the land behind the

Dunkin Donuts property and construct a separate signalized intersection to allow traffic to move

from Route 1A SB to Route 1. See Figure A2 in the Appendix.


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The third concept, Concept F, appears to be the most costly and complex of the solutions

discussed in this study. First this proposal eliminates the connection between Routes 1 and 1A at

the existing intersection. The current intersection will have signalized traffic flow for the

junction of Route 1 and Elmwood St only. Approximately 400 feet south on Routes 1 and 1A

from the existing intersection, two more signalized intersections are called for installation as well

as substantial land acquisition between the two new intersections. See Figure A3 in the

Appendix.

ii. New Proposal

The new alternative designed in this study shows promise of improvements in traffic

operations by including Route 1A NB and SB traffic flow in the signalized intersection. The

unregulated traffic flow coming from those directions have been determined to be one of the

main contributors for large queue lengths, long delay times, and high accident rates. Including all

Route 1A traffic into the existing signal phasing and opening up the intersection into one 5-

phased intersection, shows potential to be a legitimate solution to this problem. Originally in the

new design, each approach had its own phase and appropriate green times were designated based

on incoming volumes. This method at first seemed like a viable solution until the software ran

the simulation, and extremely large traffic queues and delays occurred. The next step in altering

this design was figuring out how to properly manage the signal phasing and timing sequences to

minimize traffic back up.

This proposal calls for four additional lanes to be constructed in the already limited area

of the intersection. The high peak volumes cannot be successfully managed with the current

number of lanes in attempt to include all the Route 1A traffic into the signalized system. Right

turn lanes are to be constructed for the Route 1 SB and Route 1A NB approaches, and left turn

lanes for the Route 1 NB and Route 1A SB approaches. From trial and error of designing how to

direct traffic and their corresponding volumes, the previously described lane additions allow formore evenly distributed traffic. With appropriate sidewalk and curb adjustments, the additional

lanes called for in this design can be successfully constructed within the limited area of the

intersection. For both peak morning and evening existing traffic volumes, only 5 vehicles per

hour travelled from Route 1 southbound to Route 1A north, so this movement was eliminated or

sacrificed in this design. See Figure 7 for the simplified Microsoft Excel drawing of the proposed


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intersection layout. From the 2010 peak AM and PM approach volumes, the number of vehicles

per hour for each lane are shown in Figure 7 as well. The peak PM volumes are shown in

parentheses below the peak AM volumes. The solid and dashed lines represent protected and

unprotected traffic movements, respectively. Refer to Figure B1 in Appendix B for the proposed

layout over the existing intersection.

Figure 7 Proposed Intersection Layout

Now that the number of lanes and corresponding vehicle volumes have been determined,

the signals can be phased and timed. The heaviest volumes of non-conflicting traffic are the

Route 1 and Route 1A NB to SB and SB to NB approaches. Those movements were grouped

together and designated Phase 2. Since Route 1 NB has such a large approach volume, the next


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phase (Phase 3) consists of all Route NB protected movements. Phase 4 allows for Route 1 SB

and Route 1A NB protected right turns. Phase 5 allows traffic from Elmwood St to freely move

in all directions. Phase 1 accommodates the last approach for all Route 1A SB left turns, and also

gives the Route 1A SB straight approach a green signal. The phases move in numeric order from

lowest to highest, and then cycle from Phase 1. Standard pedestrian buttons are to be included to

accommodate a phase for pedestrian volumes.

The appropriate green times for each phase can be calculated now that the movements of

each phase have been determined. Typically the critical approach volume would be used for

green time calculations, but since this system has overlapping phases, the maximum volumes

were neglected for phases 1 through 3. Using equations 5 and 6, the design green times can be

determined. See Tables 12 and 13 for the peak AM and PM green time analyses, respectively.

Cycle Length, C Equation 5

Where,

= Saturation Headway (seconds / vehicle)N = Number of Phases

= Total Loss Time (seconds)Vc = Critical Lane-Flow (vph)Note values for V c calculated in Tables 11 and 12

Peak AM Cycle Length

Peak PM Cycle Length

Available Green Time, G Equation 6

Where,


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C = Cycle Length (second)N = Number of Phasesy = Yellow Time (s)ar = All Red Time (s)

Peak AM Available Green Time Peak AM Available Green Time

Table 12 Cycle Length and Green Time Determination for Peak AM Volumes

Phase

MaxVol.(vph)

DesignUse

(vph)

CycleLength

(s)

TotalAvailable

Green Time (s)

% of TotalDesignUse (%)

GreenTime

(s)

DesignGreen

(s)1 170 90

80.0 50.0

9.9 4.945055 5.0

2 393 260 28.6 14.28571 14.03 393 180 19.8 9.89011 10.04 240 240 26.4 13.18681 13.05 140 140 15.4 7.692308 8.0

Total 1,123 910 100.0 50.0 50.0

Table 13 - Cycle Length and Green Time Determination for Peak PM Volumes

Phase

MaxVol.(vph)

DesignUse

(vph)

CycleLength

(s)

TotalAvailable

Green Time (s)

% of TotalDesign

Use

GreenTime

(s)

DesignGreen

(s)1 405 250

120.0 90.0

20.9 18.82845 19.02 395 395 33.1 29.74895 30.03 228 130 10.9 9.790795 10.04 205 205 17.2 15.43933 15.05 215 215 18.0 16.19247 16.0

Total 1,448 1,195 100.0 90.0 90.0

From Tables 12 and 13, different cycle lengths and green times were computed for the

AM and PM conditions. Since the PM volumes generated a larger critical lane flow in this

phasing design, the cycle length calculated from Equation 5 is 40 seconds larger. This means that

the morning green times need to increase accordingly for the necessary green times to handle the

evening peak volumes. During the morning commute, green times will follow the lengths

provided in Table 12 and in the evening, green times should follow the values provided in Table

13. These tabulated green times are designed to handle peak flows so, detectors are


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recommended for all approaches to help facilitate the flow of traffic by decreasing waiting time

of drivers when there are smaller approach volumes.

The signal phasing and timing sequences are compiled in Tables 14 and 15. The green

times shown in the following tables are the maximum green times allotted to each phase. The

green, yellow, red, and all red signals are represented with the symbols G, y, R, and ar,

respectively. Minimum green times were not determined in this study since the analysis was

conducted using fixed signal times for peak volumes. If this design were to be implemented, the

traffic engineer should calculate appropriate minimum green times and vehicle extensions for

pavement detectors when there are smaller traffic volumes.

Table 14 Peak AM Signal Phasing and Timing Sequence

Approach Phase1 2 3 4 5

Route 1 NBStraight

R11

G20

G10

y4

ar2

R19

R14

Route 1 NBLeft

R11

R20

G10

y4

ar2

R19

R14

Route 1 SBStraight

R11

G14

y4

R2

R16

R19

R14

Route 1 SBRight

R11

R20

R16

G13

y4

ar2

R14

Route 1A NBStraight

R11

G14

y4

R2

R16

R19

R14

Route 1A NBRight

R11

R20

R16

G13

y4

ar2

R14

Route 1A SBStraight

G11

G14

y4

R2

R16

R19

R14

Route 1A SBLeft

G5

y4

ar2

R20

R16

R19

R14

Elmwood St R11R20

R16

R19

G8

y4

ar2

Cycle Length = 80 seconds


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Similarly to the simulations of the existing data, the program output average delay times

for the proposed design with the peak AM and PM volumes. The mean delay times were then

used to compute the expected delay times within the 85% confidence bounds, as shown in

Equation 4. These delay times from the simulations of the morning and evening peak flows are

shown in Tables 16 and 17, respectively.

Table 16 - Simulated Proposed Design Mean Peak AM Delay Times, (s)

Approach Mean (s) Standard Dev 85% Confidence Boundsfor Mean Delay (s) LOS Route 1 NB Straight 9.6 4.6 6.7 12.6 A - B

Route 1 NB Left 14.1 1.1 13.4 14.8 BRoute 1 SB Straight 11.3 1.2 10.6 12.1 B

Route 1 SB Right 5.4 1.7 4.3 6.5 ARoute 1A NB Straight 20.3 1.4 19.4 21.2 B - CRoute 1A NB Right 19.0 1.8 17.8 20.1 B - C

Route 1A SB Straight 9.3 1.6 8.3 10.4 A - BRoute 1A SB Left 22.7 3.4 20.5 24.9 C

Elmwood St 17.5 2.0 16.2 18.8 B

Table 17 - Simulated Proposed Design Mean Peak PM Delay Times, (s)

Approach Mean (s) Standard Dev 85% Confidence Bounds

for Mean Delay (s)LOS

Route 1 NB Straight 18.9 1.0 18.2 19.5 BRoute 1 NB Left 29.5 4.6 26.6 32.5 C

Route 1 SB Straight 45.5 2.6 43.8 47.2 DRoute 1 SB Right 51.9 5.7 48.2 55.5 D

Route 1A NB Straight 22.4 1.3 21.6 23.2 CRoute 1A NB Right 31.8 6.5 27.6 36.0 C - D

Route 1A SB Straight 35.9 3.2 33.9 38.0 C - DRoute 1A SB Left 74.9 3.0 72.9 76.9 E

Elmwood St 37.1 3.2 35.1 39.2 D


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VII. Discussion of Results

The proposed design of the Route1, Route 1A, Elmwood St intersection more evenly

distributes traffic than the current design. Opening up the signalized intersection, adding

protected turning lanes, and altering the signal phasing and timing sequence has shown

significant results through the simulation software. For both peak AM and PM volumes, these

improvements have alleviated traffic congestion and dispersed the delay times somewhat evenly

for all approaches. Refer to Tables 18 and 19 for the 85% confidence bounds for the quality of

service comparisons for the proposed versus existing conditions for both peak AM and PM

volumes.

Table 18 - Comparing Peak AM Proposed vs Existing Delay Times

Approach Proposed DesignDelay (s) LOSExisting Design

Delay (s) LOS

Route 1 NB Straight 6.7 12.6 A - B 5.6 6.4 ARoute 1 NB Left 13.4 14.8 B

Route 1 SB Straight 10.6 12.1 B 2.6 3.5 ARoute 1 SB Right 4.3 6.5 A

Route 1A NB Straight 19.4 21.2 B - C

64.0 78.0 ERoute 1A NB Right 17.8 20.1 B - C

Route 1A SB Straight 8.3 10.4 A - BRoute 1A SB Left 20.5 24.9 C

Elmwood St 16.2 18.8 B 9.6 10.8 - B

Table 19 - Comparing Peak AM Proposed vs Existing Delay Times

Approach Proposed DesignDelay (s) LOSExisting Design

Delay (s) LOS

Route 1 NB Straight 18.2 19.5 B 3.0 3.8 ARoute 1 NB Left 26.6 32.5 C

Route 1 SB Straight 43.8 47.2 D 53.6 74.6 D - ERoute 1 SB Right 48.2 55.5 D

Route 1A NB Straight 21.6 23.2 C - C

92.4 115.8 FRoute 1A NB Right27.6 36.0 C - D

Route 1A SB Straight 33.9 38.0 C - DRoute 1A SB Left 72.9 76.9 E

Elmwood St 35.1 39.2 D 13.6 14.3 B


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VIII. Conclusions

The new design shows promise as an alternative solution to improving traffic operations

at this intersection. Based on the simulations with peak volumes, this design is effective in

regulating traffic through this intersection. The proposed changes require little construction and

land acquisition compared to some of the alternatives submitted to the North Attleborough Board

of Public Works. Obviously how improving this intersection will be funded has been a great

concern for the BPW, and this approach to upgrading the intersection should be less expensive

than other alternatives. This new proposal will be given to the Board of Public Works as well as

the hired engineering firm, BETA Group, for analysis and comparison against the previously

submitted alternatives.

As previously mentioned, minimum green times and detector vehicle extensions were notdetermined in this study. This proposal was able to determine how well this design was able to

handle the measured peak volumes with maximum fixed green times. If this proposal were to be

used as a solution to fix this intersection, the traffic engineers will have to determine the

appropriate lengths for these other signal parameters. The exact locations for stop lines and curb

adjustments for the proposed lane additions were also not determined. In order to accommodate

these additional lanes, the median between southbound approaches and the Route 1SB approach

stop line must be moved back roughly 100 feet northbound of the existing location. The limited

amount of space does not allow for additional lanes in both the Route 1 and 1A SB directions

without this adjustment. This new design will also require appropriate pavement markers

directing traffic to eliminate movement confusion and increase safety. The balance of minimal

construction costs to improved traffic operations for this proposal appears to be a viable solution

to amending this intersection.


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IX. References

1. Intersection Design. Massachusetts Highway Department, 2006.

2. Cabral, Steven P.E. Crossman Engineering, Inc. Town of North Attleborough Board of

Public Works. 20123. Chaudhary, N., C. Chu, S. Sunkari, and K. Balke. Guidelines for Operating Congest

Traffic Signals. Texas Transportation Institute, 2010.

4. DeGray, Jason. BETA Group, Inc. 2012

5. DeMelia, A. At a Dead End - Proposals to Fix Busy North Intersection Proving

Complicated and Costly. Sun Chronicle, Vol. News, No.

http://www.thesunchronicle.com/articles/2012/02/14/news/10969045.txt , 2012.

6. Google Inc. Google Earth. , Vol. 5.1.3533.1731, 2009.

7. Last, M., G. Avrahami, and A. Kandel. Using Data Mining Techniques for Optimizing

Traffic Signal Plans at an Urban Intersection. International Journal of Intelligent Systems,

Vol. 26, No. 7, 2011, pp. 603-620.

8. Massachusetts Highway Department. Project Development and Design Guide.

http://www.vhb.com/mhdGuide/mhd_Guidebook.asp , Accessed February, 2012.

9. MassDOT. Average Crash Rates.

http://www.mhd.state.ma.us/default.asp?pgid=content/traffic/crashrate&sid=about ,

Accessed February, 2012.

10. McShane, W., E. Prassas, and R. Proses. Traffic Engineering. Pearson, New Jersey, 2011.

11. NCHRP. Evaluating Intersection Improvements: An Engineering Study Guide.

Transportation Research Board, National Research Council, 2001.

12. PTV Vision. VISSIM. , Vol. 5.3, 2010.
http://www.thesunchronicle.com/articles/2012/02/14/news/10969045.txthttp://www.thesunchronicle.com/articles/2012/02/14/news/10969045.txthttp://www.vhb.com/mhdGuide/mhd_Guidebook.asphttp://www.vhb.com/mhdGuide/mhd_Guidebook.asphttp://www.mhd.state.ma.us/default.asp?pgid=content/traffic/crashrate&sid=abouthttp://www.mhd.state.ma.us/default.asp?pgid=content/traffic/crashrate&sid=abouthttp://www.mhd.state.ma.us/default.asp?pgid=content/traffic/crashrate&sid=abouthttp://www.vhb.com/mhdGuide/mhd_Guidebook.asphttp://www.thesunchronicle.com/articles/2012/02/14/news/10969045.txt


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X. Appendix A Figure A1 BETA Group, Inc Concept C-3


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Figure A3 BETA Group, Inc Concept F


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XI. Appendix BFigure B1 Proposed Intersection Design


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Figure B2 Phase 1 (Route 1A SB, All Movements) on VISSIM

Figure B3 Phase 2 (Routes 1 and 1A, NB and SB Straight) on VISSIM


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Figure B4 - Phase 3 (Route 1 NB, All Movements) on VISSIM

Figure B5 Phase 4 (Route 1 SB and Route 1A NB Right Turns) on VISSIM


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Figure B6 Phase 5 (Elmwood St, All Movements) on VISSIM

cen 519 paper (cabral)

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