FINAL PAPER

J A K E n g i n e e r i n g S e r v i c e s , I n c . P a g e | 0
Cobb Parkway (US 41) and Windy Hill
Road IntersectionImprovement
CE 4800 Senior Project, Summer of 2015
Group 5: John Pulicare, Alex Harrington,
and Katelyn Niemann

Table of Contents
1. Introduction................................................................................................................................3
2. Design Considerations .................................................................................................................3
2.1 Traffic andPedestrian Counts...................................................................................................3
2.2 Signal Phasing..........................................................................................................................4
2.3 Level of Service (LOS)-Alex .......................................................................................................4
3. Design Alternatives......................................................................................................................4
3.1 Alternative 1 ...........................................................................................................................5
3.2 Alternative 2 ...........................................................................................................................6
3.3 Alternative 3 ...........................................................................................................................6
3.4 Alternative 4 ...........................................................................................................................7
3.5 Alternative 5 – Central Turn Overpass (CTO)..............................................................................8
4. Drawings and Calculations ...........................................................................................................9
4.1 Final Plan Set...........................................................................................................................9
4.2 Bridge Design..........................................................................................................................9
4.3 Syncro Data...........................................................................................................................10
5. Environmental Studies...............................................................................................................10
5.1 Streams................................................................................................................................10
5.2 Wetlands ..............................................................................................................................10
5.3 Lakes and Ponds....................................................................................................................11
5.4 Floodplains............................................................................................................................11
5.5 Conservation Areas/Parks(Section 4f) ....................................................................................12
5.6 Land and Water Conservation (Section 6f) ..............................................................................13
5.7 Protected Species..................................................................................................................13
5.7.1 Animal Occurrences...........................................................................................................13
5.7.1.1 Birds.................................................................................................................................13
5.7.1.2 Fish...................................................................................................................................13
5.7.1.3 Amphibian.........................................................................................................................13
5.7.1.4 Mollusks............................................................................................................................13
5.7.1.5 Reptile ..............................................................................................................................13
5.7.1.6 Crustacean........................................................................................................................13
5.7.2 Plant Occurrences..............................................................................................................13
5.8 Noise Receptors ....................................................................................................................14

5.9 Environmental Population......................................................................................................14
5.10 Farmland...............................................................................................................................15
5.11 Displacements.......................................................................................................................15
5.12 Historic Properties.................................................................................................................16
5.13 Archeologic Locations............................................................................................................16
5.14 Cemeteries............................................................................................................................16
5.15 Native American Interests......................................................................................................16
5.16 Air Quality.............................................................................................................................17
5.17 Indirect and Cumulative Impacts ............................................................................................17
5.18 Construction Impacts.............................................................................................................17
5.19 Mitigation Evaluation.............................................................................................................17
6. Summary..................................................................................................................................17
7. References................................................................................................................................18
8. Appendix ..................................................................................................................................19

1. Introduction
The intersection of Windy HillRoad and Cobb Parkway (US 41) is rated as one of the leastefficient
intersection in the state of Georgia. The intersection is located in Marietta, Georgia, is
surrounded by businesses on all four sides, and is a direct route to the nearby Interstates 75 and
285. These factors as well as many others make for heavy traffic volumes, as there is no nearby
roads able to handle the vehicle capacities. The current intersection is not sufficient to handle
the loads and therefore there are excessive delays.
The following proposal will investigate the advantages and disadvantages of plausible
improvements to the intersection to increase safety and the level of service of the intersection
as well as detailed calculations of the final design called a Central Turn Overpass (CTO) and
corresponding drawings.
2. Design Considerations
Field studies are done in order to collect the required data on the intersection in order to make
an informed decision on which alternative should be selected. Studies include traffic counts,
pedestrian counts, signal phasing, and research for unconventional intersection designs.
2.1 Traffic and Pedestrian Counts
Traffic counts are conducted by counting the number of vehicles passing through each lane and
the direction the vehicles are passing through in 15 minute intervals. The peak hour is then
determined by finding the largest sequential 15 minute interval traffic vehicle counts. The peak
hour for Windy Hill and Cobb Parkway was determined to be between 5:00 PM and 6:00 PM with
an average of 905 vehicles per 15 minute interval and 3,621 vehicles during the peak hour, as
seen in Figure 2.1 below.
Figure 2.1: Traffic Counts
THRU NORTH SOUTH EAST WEST
715 358 277 229 333
713 351 271 238 313
693 317 259 230 354
765 343 274 262 392
818 377 282 240 387
735 338 280 256 395
828 395 262 243 415
826 412 310 221 431
925 516 262 243 487 Peak hour
902 575 277 183 405
924 524 301 240 471 PEAK 15 Min
870 513 291 193 478
828 427 298 227 444
804 425 277 215 438
734 395 269 202 380
711 349 253 197 363
SUMS:
12791 6615 4443 3619 6486

2.2 Signal Phasing
Signal phasing timing is determined by timing each green, yellow, and red time for each lane and
direction. Signal phasing was determined as about 170 second total cycle with varied green,
yellow, and red times per lane. Signals for Windy Hill directions remain on the same phases while
Cobb Parkway have differing phasing due to different left turn phasing. Detailed phasing is
available in the appendices.
2.3 Level of Service (LOS)-Alex
Level of service (LOS) is a widely used term to refer to the system in which intersections can be
rated and compared. LOS rates how well an intersection is operating based on average delay and
uses a scaleof“A” through “F” as shown in Figure 2.3. LOS is determined using the phasing times,
traffic counts, and speed limits collected from field studies amongst other factors. A level of “A”
through “D” is considered acceptable whereas “E” and “F” are not.
Figure 2.3: Level of Service Scale
The current signal has a level of service of F. The average delay of the entire intersection is 163.9
seconds. Less than 80 seconds of delay is needed to reach a level of service of E. Most notably,
the Windy Hill Rd eastbound left turn lane has an average delay of 675.1 seconds which is more
than eleven minutes. Detailed calculations are available in the appendices.
3. Design Alternatives
Before any alternatives were selected,the intersection was studied in the fieldduring peak hours.
Many obvious issues were clearly visible during this time. One of those issues was vehicles lining
up in the left turn queue before the storage started and others at the end of the taper would just
into the through lanes effectively taking away the use of one through lane. In order to improve
this issue,itwas proposed that the left turn lanes would be analyzed and extended where needed
(henceforth known as alternative 1).
The entire intersection showed significant delay but what we reasoned to be the root of the
problem was the even more significant delay in the left turns. We inspected that the left turn
phases were too short and only a few out of many vehicles would make it through the

intersection each cycle. In order to improve this issue, it was proposed that the signal timing be
optimized with emphasis on increasing the left turn durations (henceforth known as alternative
2.)
In order to address the delay in the through lanes, auxiliary right turn lanes and additional
through lanes were proposed (henceforth known as alternative 3). Alternative 3 was assumed to
be the alternative that would have the greatest improvement to the intersection but at the
greatest cost.
Another alternative that was proposed was to change the layout and configuration entirely with
the construction of a roundabout (henceforth known as alternative 4). It was our hope that a
new layout would improve traffic conditions as roundabouts would not utilize signal phasing.
Finally, a Center Turn Overpass (CTO) was suggested. A CTO overpass addresses the need to
improve left-turn movements in all directions of traffic by elevating the left turn lanes via ramps.
Because the left turn phasing is so poor in all directions, we decided this was the most viable
option presented due to its success in elevating the overall intersections level of service.
3.1 Alternative 1
At the intersection of Windy Hill Rd and Cobb Pkwy, the existing left turn lanes going northbound
and eastbound are too short for the peak hour of traffic. The existing left turn lane for Cobb Pkwy
Northbound is 307 ft with a 50 ft taper. The existing left turn lane for Windy Hill Rd Eastbound is
225 ft with a 50 ft taper. These are the most critical turn lanes in the intersection. Cobb Pkwy
Southbound is 380 ft with a taper of 81 ft. Windy Hill Rd Westbound is 643 ft with a taper of 54
ft. During the peak hour of traffic, cars trying to get into the left turn lane block cars that are just
staying in the through lane. The level of service for both of these left turn lanes is F.
Adjustments had to be made to the left turn lengths to allow for the max flow into the left turn
lanes. The left turn lane for Cobb Pkwy Northbound was extended to 430 ft. The left turn lane for
Windy Hill Rd Eastbound was extended to 425 feet. The taper for both lanes remain the same.
There were no adjustments for Cobb Pkwy Southbound and Windy Hill Eastbound. Both of these
left turn lanes are already at the max distance that they can extended to.
The level of service for the existing intersection is F, and after the lanes were extended the level
of service remained an F. Note that with lane extensions you will rarely have a change in the level
of service. Just because the lane has been extended doesn’t mean that more cars will be able to
get through the short light. However, the lane extension allows for more cars that need to turn
left to get into the turn lane earlier which allows more people to make the green light in the
intersection before Windy Hill Rd and Cobb Pkwy. Driving can be very stressful during the peak
hour of traffic, and allowing cars to move into the left turn lane sooner will makes the drivers feel
like they are actually going somewhere when there is really bad traffic. The level of service didn’t
change when the lanes were extended, but the drivers turning left will be more pleased with the
ability to move into the turn lane faster.

Figure 3.1: Visual reference for Alternative 1
3.2 Alternative 2
The existing signal has a cycle length of 167 seconds. The all red time for all phases is 2 seconds.
The Windy HillRd left turn phase is 12 seconds of green with 4 seconds of yellow and the through
phase is 47 seconds of green with 6 seconds of yellow. The Cobb Pkwy left turn phase is 20
seconds of green with 4 seconds of yellow and the through phase is 60 seconds of green with 6
seconds of yellow.
The signal timing was optimized to provide the best service for the entire intersection. The new
signal timing has a cycle length of 170 seconds. The all red time for all phases is still 2 seconds.
The Windy Hill Rd left turn phase is 18.5 seconds of green with 4 seconds of yellow and the
through phase is 45.4 seconds of green with 6 seconds of yellow. The Cobb Pkwy left turn phase
is 19.5 seconds of green with 4 seconds of yellow and the through phase is 58.6 seconds of green
with 6 seconds of yellow.
Note that the optimized signal timing increases the left turn phase by 6.5 seconds. This change
decreases the total delay of the entire intersection to 141.8 seconds. This is still a level of service
of F. While the delay for the entire intersection only decreases by 22.1 seconds, the decrease in
delay for the eastbound left turn is much more significant. The average delay for the eastbound
left turn would be 320.9 seconds. This is still a poor average delay and a level of service of F but
it decreases the existing delay by 354.2 seconds which is almost 6 minutes. (See Appendix Figure
8.2)
3.3 Alternative 3
Due to the largecommuter community that surrounds the intersection, the peak hour is over 900
vehicles every 15 minutes, which is over 3600 vehicles per hour. Of the 900 vehicles, over 500
are going northbound during the evening rush hour and southbound during the morning rush
hour, therefore making the through lanes on Cobb Parkway is the most relevant to check.
In order to address these large traffic flows, an option is proposed to add an additional lane both
southbound and northbound in order to let more vehicles through without changing the signal

phasing and therefore changing the traffic flows of the competing directions. In order to achieve
the extra lane on Cobb Parkway, the current auxiliary right turn lanes are going to be used for
the through lanes and the additional lane would be added on the outside of the current right turn
lane to become the new right turn lane. This alternative provides the largest change in level of
service due to the largest number of vehicles able to pass through the intersection without
altering the other directions.
Due to the expansion of a large stretch of road that is already surrounded by existing buildings,
costs would be very high. Possible demolition of the existing buildings may apply and the cost of
materials and labor would be the largest portion of the budget. Safety issues also become an
issue as alternate pedestrian walks would need to be provided as the current intersection is
surrounded by several bus stops.
Figure 3.3: Visual reference for alternative 3
3.4 Alternative 4
Cobb Parkway and Windy Hill is heavily congested and we believed that the signal phasing was a
plausible cause for a lot of the congestion that occurs. A roundabout is utilized in order to
eliminate the need for signal phasing for an intersection. Typical roundabouts connect roads that
consist two to three lanes entering the respective roundabout. However, larger roundabout may
have connecting roads that have four to five lanes. Naturally, we believed that since the
intersection has so much trafficflowing through it on aday to day basis,we would need to design
one of these larger roundabouts. Though with more lanes, and with the concept of the
roundabout being relatively new in the United States, more confusion may be apossibleoutcome
of installing a roundabout.
We contacted the Georgia Department of Transportation about the installation of a roundabout
and they referred us to the GDOTRoundabout Tool. The GDOTRoundabout Tool is a spreadsheet
that allows a design firm to input the existing data for an intersection. In turn, the tool calculates
a potential new level of service. Because the a roundabout in considered to be a complex and
time consuming design, a preliminary tool such as this is necessary to determine whether or not
it is a viable option before further design work continues. After utilizing and inputting the
information provided to us by the Cobb County of Transportation, the tool determined the

intersection would still achieve a grade of F. In conclusion, a roundabout proved to be an
implausible alternative.
3.5 Alternative 5 – Central Turn Overpass (CTO)
After calculations and observation, it seemed the alternatives listed above did not improve the
intersection as needed. In turn, another option was proposed, the Center Turn Overpass (CTO).
A CTO overpass addresses the need to improve left-turn movements in all directions of traffic
by elevating the left turn lanes via ramps within the median of each direction. Because this
structure will be implemented within the median of each direction, this would drastically
reduce the amount of space needed for the improvement as well as eliminate the need for
relocation of surrounding structures and businesses.
These ramps will elevate the left turn lanes of each respective direction and will follow separate
turn phase signaling fromthe intersection below which will function as per normal. Because of
this movement separation, the structure requires a merging and deceleration lane will which
also provide easy merging for the traffic flowing off the ramp into the existing on-grade
intersection below. As a result of the signal separation, the intersection below will have
shortened signal phasing and will decrease the overall cycle length and delay. In addition to the
addition of CTO, we decided to include auxiliary lanes for each respective right turn. This
consideration would further the decrease the delay of the intersection by separating right turn
traffic from the through traffic in each direction. After calculation and observation, the level of
service of the intersection increased from an F to a B due to implementation of the CTO making
it the best alternative to address the improvement of the intersection.
Figure 3.5: Visual reference for alternative 5

4. Drawings and Calculations
The following sections describe the engineering plan set of drawings proposed to conduct a CTO
intersection at Windy Hill and Cobb Parkway, the bridge design, and traffic modeling in Syncro.
4.1 Final Plan Set
The attacheddocumentsare anengineeringplansetof drawingdetailingthe proposedintersectionusing
a CTO design provided by JAK Engineering, Inc. Calculations may be found in the appendix section.
4.2 Bridge Design
The bridges in our design serve as left turn overpasses for the intersection below and will serve
two lanes of traffic flow. Because each bridge is identical, qualities will be discussed as a singular
bridge and henceforth will be referred to as such. The bridge is 110 feet total in length, 33 feet
end to end, and 24 feet gutter to gutter. These width will provide enough space in order for the
largest design vehicle to make a proper left turn. In either direction, a 500 foot M.S.E. wall will
proceed at a 4.4% grade before the beginning of each bridge (standard details apply). The bridge
is a structural truss and designed to support 110.9 kips per foot. The truss primarily consists of
16 HSS 8x8x3/16 beams cut to specification. Column supports are spaced 19’-3’’on center and
support a compressive load of 186 kips each. The bridge is laterally support by 21 HSS 8x8x5/16
every five feet on center. The bridge has 20 feet of clearance from the intersection. The truss
system also provides 20 feet of clearance from the bridge traffic and will support traffic signals
for each respective direction. The bridge itself supports a 6 inch pavement surface as well as one
inch metal decking throughout. It will also consist of a 2’-1” high standard 2-beam metal guard
rail that sits on a standard 7 inch curb. Each lateral beam of the guard rail is a 5x5x5/15 and is
supported by 8”x24” spaced every 8 feet on center. (See Appendix Figure 8.6-8.9)
Figure 4.2.1: Elevation view of Windy Hill Road left turn access bridge over Cobb Parkway

Figure 4.2.2: Plan view of Windy Hill Road left turn access bridge over Cobb Parkway
4.3 Syncro Data
The program Synchro 7 was used to model the traffic and calculate the delay of the new
intersection. After the Center Turn Overpass was designed to fit the intersection of Windy Hill Rd
and Cobb Pkwy, its exact specifications were inputted into Synchro. Once the model matched the
design, the traffic flows and optimized signal times were also inputted into the program. Synchro
used this information as well as some standard factors to calculate the level of service. The level
of service for the entire intersection was found to be a “B” with a total average delay of 16.1
seconds for the lower intersection and 13.4 seconds for the upper intersection. That is an
improvement of 147.8 seconds from the current state of the intersection. Also, for the worst
portion of the intersection (the Windy Hill EB left turn) it is an improvement of eleven minutes.
The full report is in Appendix XXXX.
5. Environmental Studies
The intersection of Cobb Parkway and Windy Hill Road is in a developed urban area and lies in
the middle of several strip malls and businesses. In turn, the area of interest lacks most
environmental concern based on previous work and construction. Alternatives have been
developed to avoid as much environmental impact as possible.
5.1 Streams
The immediate area of interest does not have any rivers or intermittent streams present. Nearest
intermittent/ephemeral streams:
· Poplar Creek - 0.7 miles South on Cobb Parkway
· Nameless stream - 0.5 miles North on Cobb Parkway
5.2 Wetlands
The wetlands (freshwater/forested shrub category) were evaluated using National Wetlands
Inventory digital Geographic Information Systems (GIS) data. Wetlands were counted within an

analysis radius of 1000 feet of the area of interest. In conclusion, no wetlands are present within
the area of interest.
Figure 5.2 NWI Aerial Imagery
http://www.fws.gov/wetlands/data/Mapper.html
5.3 Lakes and Ponds
The freshwater lakes and ponds were evaluated using National Wetlands Inventory digital
Geographic Information Systems (GIS) data. These bodies of water were counted within an
analysis radius of 1000 feet of the area of interest. In conclusion, no freshwater lakes or ponds
are present within the area of interest. Please see Figure 5.2.
5.4 Floodplains
Federal Emergency Management Agency (FEMA, 2012) digital GIS data for Special Flood Hazard
Areas were used for Cobb County. These bodies of water were counted within an analysis radius
of 1000 feet of the area of interest. In conclusion, the area of interest does not fall within any
floodplain. Please see Figure 5.4

.
Figure 5.4 FEMA Floodplain Aerial Imagery
5.5 Conservation Areas/Parks (Section 4f)
Section 4(f) refers to the USDOT Act of 1966, which provides that FHWA cannot use land from
publicly owned parks, recreation areas, wildlife and waterfowl refuges, or public and private
historical sites unless this is no feasible and prudent alternative and all efforts to minimize harm
have been conducted (as per FHWA http://environment/fhwa.dot.gov/(S(1vyep454s3wmhuu-
bnvexkmm2))/4f/index.asp). According to NARSAL (Natural Resources Spatial Analysis Lab
provided by UGA), the area of interest does not fall within any conservations or parks. The only
conservations of note in the area are Dobbins Air force Base, Legacy Golf Links, and Fox Creek
Golf Links. Please see Figure 5.5.
Figure 5.5 NARSAL Aerial Imagery
http://narsal.uga.edu/maps/georgia-conservation-lands/

5.6 Land and Water Conservation (Section 6f)
Maps of Section 6(f)lands (lands acquired with Land and Water Conservation Funds [LWCF])were
compiled from the list of conservation lands and cross-checked with Cobb County lists for areas
receiving LWCF funding. The area of interest does not fall within any LWCF Projects. Dobbins Air
force base is the closest LWCF area.
5.7 Protected Species
Cobb County is home to several rare species of plants and animals of whose habitats should be
taken into account. They include:
5.7.1 Animal Occurrences
5.7.1.1 Birds
 Ammodramus henslowii (Henslow's Sparrow) *
 Nyctanassa violacea (Yellow-crowned Night-heron)
 Ammodramus henslowii (Henslow's Sparrow)
5.7.1.2 Fish
 Cyprinella callitaenia (Bluestripe Shiner) *
 Etheostoma scotti (Cherokee Darter) **
 Hybopsis sp. 9 (Etowah Chub)
 Micropterus cataractae (Shoal Bass)
 Notropis hypsilepis (Highscale Shiner) *
5.7.1.3 Amphibian
 Hemidactylium scutatum (Four-toed Salamander)
 Plethodon websteri (Webster's Salamander)
5.7.1.4 Mollusks
 Medionidus penicillatus (Gulf Moccasinshell) **
 Elliptio arctata (Delicate Spike) *
 Quadrula infucata (Sculptured Pigtoe)
5.7.1.5 Reptile
 Pituophis melanoleucus melanoleucus (Northern Pine Snake)
5.7.1.6 Crustacean
 Cambarus howardi (Chattahoochee Crayfish) *
5.7.2 Plant Occurrences
 Arabis missouriensis (Missouri Rockcress)
 Calystegia catesbeiana ssp. sericata (Silky Bindweed)
 Cypripedium acaule (Pink Ladyslipper) *

 Draba aprica (Sun-loving Draba) *
 Melanthium latifolium (Broadleaf Bunchflower)
 Nestronia umbellula (Indian Olive) *
 Platanthera integrilabia (Monkeyface Orchid) **
 Pycnanthemum curvipes (Stone Mountain Mint)
 Rhus michauxii (Dwarf Sumac) **
 Schisandra glabra (Bay Star-vine) *
 Symphyotrichum georgianum (Georgia Aster) **
 Trillium lancifolium (Lanceleaf Trillium)
 Zanthoxylum americanum (Northern Prickly-ash)
Note: * GA Protected, ** US Protected
http://georgiawildlife.com/sites/default/files/uploads/wildlife/nongame/text/html/cnty_eos/c
obb.html
Given the scope of the project, it is unlikely any endangered species’ habitats will affected.
5.8 Noise Receptors
Aerial photography was used to identify structures and attraction that may qualify as noise
receptors. Fox Creek Golf Course and Driving Range is 1.7 miles west on Windy Hill Road. Given
the nature of the activity being performed at the golf club, the noise could be a potential
inconvenience. Other parties that may be considered noise receptors are local business in the
immediate area. These include:
 Nalley Infiniti
 Folk’s Southern Kitchen
 Guitar Center
 Car Spa
 Chevron
 I love Sushi
 Western Union
 Haverty’s
5.9 Environmental Population
Statistics were gathered based on ‘place’ and ‘county’ from the US Census Bureau. A comparison
of minority population and household income was performed to demonstrate whether or not
the area of interest is affected socially. Low-income populations are defined by the Department
of Health and Human Services in the census data. Minority is defined as a race and ethnicity that
is anything other than non-Hispanic White alone. Examples of minority populations include
African American, Hispanic or Latino, and Asian American.
Marietta, GA Percent Cobb County, GA Percent

Northern America 0.8 Northern America 1.9
Latin America 71.6 Latin America 53.4
Oceania 0.2 Oceania 0.4
Africa 8.7 Africa 10.4
Asia 13.2 Asia 24.5
Europe 5.6 Europe 9.4
Figure 5.9.1 Nativity and Foreign Born Statistics
Marietta, GA Income
Male $39,397.00
Female $39,199.00
Cobb County, GA Income
Male $56,785.00
Female $44,090.00
Figure 5.9.2 Median Earnings for Full-Time Year-Round Workers by Sex in 2008-2012
Source: US Census Bureau
According to the statistics, the construction would be affecting low-income and minority
populations.
5.10 Farmland
According to the Geographic Information Systems (GIS) County Soil Survey data for Cobb County,
the area of interest does not interfere with any farmland or areas with prime farmland soils.
5.11 Displacements
Potential displacements analysis is an evaluation to determine the number of businesses,
residents, and institutions that will need to be relocated when the project is constructed. This
analysis was developed to determine the impact that each of the alternatives will have if
constructed. No displacement should be performed considering the alternatives will not impede
on any existing structures.

5.12 Historic Properties
According to Georgia’s Natural, Archaeological, and HistoricalResources Geographic Information
System (GNAHRGIS) database, the area of interest has no impact on any historical sites or
landmarks within a notable range.
Figure 5.12 GNAHRGIS Historic Landmarks Near the Area of Interest
5.13 Archeologic Locations
According to Georgia’s Natural, Archaeological, and HistoricalResources Geographic Information
System (GNAHRGIS) database, the area of interest has no impact on any previously recorded
archaeological sites or landmarks within a notable range.
5.14 Cemeteries
Cemeteries were counted within an analysis width of 1000 feet of the area of interest. One
cemetery property has the potential to be impacted. The area of interest is located just south of
Georgia Memorial Park Funeral Home and Cemetery/Winkenhofer Chapel off of Cobb Parkway.
5.15 Native American Interests
Native American interests were researched via GNAHRGIS and the National Register of Historic
Places. No potential Native American interests will be impacted.

5.16 Air Quality
Air quality needs to be considered while performing potential construction of this nature. Tests
need to be performed with proper equipment in order to present accurate data. Motor vehicle
studies also need to be performed based on roadway capacity.
5.17 Indirect and Cumulative Impacts
Indirect and Cumulative Impacts are those that will affect foreseeable future projects and land
development. Because the area is of an urban setting, it is plausible for the area to be subject to
future development.
5.18 Construction Impacts
The potential construction impacts analysis was performed to estimate impacts to the traveling
public, as well as nearby businesses, residents, and communities. Three categories are assessed
when performing this kind of analysis: detour potential, access during construction, and noise
during construction. The only alternatives that would affect the previous criteria pertain to
altering the intersection’s alignment.
5.19 Mitigation Evaluation
Conceptual alternatives were evaluated relative to impacts causedby construction and proposed
alternatives. The contrary conceptual alternative is to not perform intersection improvements.
However, it is the belief of the consultant that improvements need to be made to ensure the
safety and efficiency of the area of interest.
6. Summary
After implementing a CTO design, the intersection will have improved an LOS from an F with an
average delay of up to 12 minutes down to an LOS of B with an average delay of 13 seconds. The
intersection will also improve pedestrian safety, as the area is in a largely public transportation
dependent region. Because Atlanta is home to a vast commuter population, the intersection of
Windy Hill and Cobb Parkway is a vital area in need of improvement, and the CTO design will be
the best solution to the complicated problem.

7. References
"Alternative Intersections/Interchanges: Informational Report (AIIR)." United States
Department of Transportation - Federal Highway Administration. United States
Department of Transportation - Federal Highway Administration, 4 Dec. 2012. Web. 21
May 2015.
<http%3A%2F%2Fwww.fhwa.dot.gov%2Fpublications%2Fresearch%2Fsafety%2F09060
%2F009.cfm>.
"California ST-30 Bridge Rail." (n.d.): n. pag. California DOT. California DOT, 2010. Web.
2015. <http://www.dot.ca.gov/hq/esc/oe/project_plans/highway_plans/stdplans_US-
customary-units_10/viewable_pdf/b11-65.pdf>.
"Highway Design Manual." Caltrans. Georgia Department of Transportation, n.d. Web. 18 July
2015.
Mannering, Fred L., and Scott S. Washburn. Principles of Highway Engineering and Traffic
Analysis. 5th ed. N.p.: n.p., n.d. Print.

8. Appendix
Figure 8.1: Traffic and Pedestrian Counts by Direction and Time Interval
Figure 8.2: LOS Calculations
Time L Thru R Ped L Thru R Ped L Thru R Ped L Thru R Ped
3:00 59 201 121 0 40 217 45 1 87 125 40 4 36 172 54 2
3:15 33 188 105 3 29 185 44 0 99 161 39 2 44 179 67 2
3:30 42 187 138 2 40 182 40 1 81 148 33 0 39 176 54 3
3:45 36 193 144 1 41 179 40 0 108 186 33 1 48 207 56 0
4:00 40 216 140 1 38 230 37 0 97 163 30 1 36 209 50 2
4:15 36 198 150 1 41 160 47 3 119 173 40 2 42 204 59 0
4:30 37 209 146 0 42 231 45 1 102 161 18 2 35 227 62 0
4:45 31 241 179 1 41 221 37 0 113 153 30 1 39 211 78 1
5:00 44 194 150 0 85 314 34 0 133 165 35 0 33 252 69 0
5:15 28 205 131 0 61 373 44 0 124 111 37 0 35 213 78 1
5:30 35 223 169 1 53 293 46 0 149 159 36 0 42 249 82 0
5:45 49 216 186 1 65 308 25 0 121 119 42 0 33 227 84 3
6:00 36 215 188 0 47 249 36 1 111 155 40 1 43 209 67 2
6:15 45 201 167 0 67 260 31 0 101 139 45 1 31 204 64 1
6:30 33 191 148 1 42 222 38 0 101 131 42 1 36 190 72 1
6:45 32 183 126 0 38 197 33 1 92 132 37 1 33 199 60 1
ENDING DIRECTION
North 6615
South 4443
East 3619
West 6486
US 41 (Cobb Pkwy) SB US 41 (Cobb Pkwy) NB Windy Hill Rd EB Windy Hill Rd WB

Figure 8.3: Current Signal Phasing
Figure 8.4: Required Storage NW Bound
G Y R G Y R
Windy Hill EB 12.0 4.0 154.0 47.0 5.5 117.5
Windy Hill WB 12.0 4.0 154.0 47.0 5.5 117.5
Cobb Pkwy NB 25.0 4.0 141.0 66.0 5.5 98.5
Cobb Pkwy SB 16.0 4.0 150.0 57.0 5.5 107.5
Total Cycle Time: 170.0 sec
All Red Time: 2.5 sec
1 2 3 4 5
Windy Hill EB L Tru - - -
Windy Hill WB L Thru - - -
Cobb Pkwy NB - - L L/Thru Thru
Cobb Pkwy SB - - L - Thru
Time: 18.5 55.0 22.5 9.0 65.0
Left Thru
RD Direction
Phase:

Figure 8.5: Required Storage NE Bound

Figure 8.6: M.S.E. Wall Grading Calculation and Right Turn Storage Calculations

Figure 8.7: Bridge Column Spacing

Figure 8.8: Bridge Column Loading Calculations
Figure 8.9: Bridge Truss Calculations

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