--./;c 0 C ::. a. C'"T 0 c.... -i 􀁾􀀠 OJ ::!; n () 􀁾􀀮􀀠 iii j .,.1 N 0 0 a,:. » a. "0;' 0 ::l Q M iii 
HUITT-ZOLIARS Huin-ZoUars. Inc. I Engineering I Architecture ( 3131 McKinney Avenue I Suile 600 I LB 105/Dallas. Texas 75204-2416/214-871-3311/FAX 214-871-0757 October 17, 1997 Mr. John
Baumgartner, P.E. Public Works Director Town of Addison P.O. Box 144 16801 Westgrove Addison, TX 75001 RE: Addison Circle Phase II Public Infrastructure Addison Circle Geometry HZI Project
No. 01-1822-21 Dear John: Per your request, we are providing this supplemental report regarding the geometric movements on Addison Circle from Quorum Drive to Dallas Parkway including
the interaction with Spectrum Drive. There are four major areas that present unusual street conditions which would benefit from further explanation; the east leg of the round-about;
movement around the divided sections of Addison Circle; the interaction of Spectrum Drive and Addison Circle; and the approach to the Tollway at Addison Circle. SECTION "A" The geometry
of the East leg of the modem roundabout is per the design by Ourston & Doctors which is presented in a report dated November, 1995. In addition we have submitted the Phase II design
to Ourston & Doctors and they returned the enclosed letter stating that the layout is in conformance with the original design. SECTION "B" Continuing east on Addison Circle through Sections
"A" and "B", a vehicle will encounter a flush median island with a yield bar and sign which will direct traffic to the right. This vehicle will be required to yield to any traffic makIng
a Utum around the esplanade. The pavement at this location is widened to 25' back to back to allow for a WB-50 truck to maneuver around the tum. The trucks will drive on the flush median
to complete the maneuver. SECTION "c" This Section of Addison Circle is 19' back to back with head-in parking. The 19' dimension is to assist with fire coverage, however, Gordon Robbins
has stated that he needs 24 feet of width. In previous meetings we have discussed that the esplanade design should be hardscaped for the first 5 feet adjacent to the curb to allow for
the encroachment of fire vehicles. The 19' width is not intended to provide two travel lanes but does aJlow for a vehicle to pass while another vehicle is stopped waiting for a parking
space. It is possible that vehicles will try to use this space as two lanes and this may need to be controlled with additional signage in the future. SECTION "D" As a vehicle approaches
Section "D" of the roadway the choice to U-turn around the esplanade or to continue east on Addison Circle is available. Again the pavement is widened to 25' b-b for WB-50 truck traffic,
however a flush median is provided to direct the regular vehicular traffic. All approaches to the esplanade split are signed with advisory speeds of 15 m.p.h., yield signs and yield
bars per Sheet P5 of Addison Circle Phase II Public Infrastructure H:\PROJ\O1182221\JB 1 0 1797.LTR DaUas JFort Worth I Houston I EI Paso I Phoenix I Orange County 
construction plans. Continuing east to Section "E" there is a natural progression to two travel lanes marked with buttons that continues to Dallas Parkway. The current design calls for
a dual right turning movement at Dallas Parkway and the appropriate signage has been added to direct motorists. Buttons can be added at a future date to taper traffic to one lane ifthe
dual right turn does not function properly. The same conditions are encountered when traveling west on Addison Circle except at Section "D". There is a turning movement off of Dallas
Parkway via a free right tum lane onto Addison Circle. We would recommend not striping Section "D" westbound for two travel lanes even though there is sufficient width for two vehicles.
As a vehicle approaches the esplanade split there is only space for one vehicle to maneuver around the flush island. We should discourage two vehicles from entering this point side by
side. ADDISON CIRCLE /SPECTRUM DRNE INTERSECTION The intersection with Spectrum Drive will be treated as a 3-way stop under this design. Although we are providing conduit with the Phase
II construction in the event signals are required in the future, it has not been determined nor is it the intent ofthis report to analyze whether signalization is necessary. Vehicles
traveling Spectrum Drive will be required to make two stops at Addison Circle due to the split roadway. We also propose to raise the section of Spectrum Drive between Addison Circle
eastbound and Addison Circle westbound to create the illusion of a continuous esplanade area. This condition should not hamper vehicular movement as long as the intersection remains
a three way stop. If the intersection ever becomes signalized where continuous green is possible in the north south direction on Spectrum the raised section could have a negative effect
on traffic flow and safety without special controls. Special signage, speed limitations and a textural warning could be employed. As a last resort, the raised area could be lowered to
a standard roadway profile with curbs. In summary, we have addressed the channelization of passenger cars and trucks in this unusual street condition with the use of signage, flush medians
and widening of pavement in critical locations. It is our belief that this geometry will allow the street to function as planned. However, it should be monitored to see ifthe actual
actions ofmotorists warrant future adjustments. Please call ifyou have any questions or comments. Sincerely, HUITI-ZOLLARS, INC. 􀁾􀀯􀀻􀀻􀁦 E. 􀁊􀀧􀁽􀀱􀁾􀁓􀁉􀁊􀀠 David E. Meyers, P.E.
dem/psp Enclosures cc: Bryant Nail-Columbus Realty Trust H:\PROJ\O1182221\JB I01797.LTR 
,., Ourston & Doctors I MODERN ROUNDABOUT INTERCHANGES May 29, 1997 Mr. Andrew C. Oakley, P.E. Huitt-Zollars, Inc. 3131 McKinney Avenue Dallas, Texas 75204-2416 Addison Circle East Leg
Plan Review We have reviewed the subject horizontal layout and signing/striping plans. We find them to be in conformance with the original design that we completed for the other three
legs of the Addison Roundabout. We have marked up the plans to show necessary corrections for location of some signs and addition of others. We also offer the following recommendations
for the streets east of the roundabout 1. Use red curb instead of the "No Parking" signs. This will reduce sign clutter and focus drivers' attention on the roundabout Signs. 2. Use one-way
signing at both ends of the oval roadway east of the roundabout. 3. At the entrance to the oval roadway, use a yield stripe. The new version of the MUTCD.will have this yield stripe,
which would also be consistent with the yield striping at the roundabout. We look forward to the the completion of the roundabout, and we would appreciate some photographs when it is
completed. Very truly yours, 􀁒􀁰􀁲􀀧􀁪􀀺􀀧􀁦􀁖􀁾􀁄􀀠 rJ.UN 021997 <0ZS Peter Doctors, P.E. 5290 Overpass Road, Suite 212 Santa Barbara, CA 93111 805/683-1383 http://www.west-net!-owendee
Fax: 805/681-1135 
John Baumgartner From: Chris Teny Sent: Tuesday, October 26, 19998:28 AM To: John Baumgartner Subject: RE: ROUNDABOUT LETTER Then just give me the hard copy. --Original Message--From:
./ohn Baumgartner Sent: Tuesday, October 26, 19998:22 AM To: ChrisTeny Subject: RE:ROUNDABOUTLETTER Chris, I do not have a draft of the letter that you sent out on the roundabout in
the computer. However, I have hard copy that I can share with you. John --Original Message--From: Chris Terry Sent: Tuesday, October 26,19998:17 AM To: John Baumgartner Subject: RE:
ROUNDABOUT LETTER John, Please e-mail me a copy of the previous letter you prepared for my signature on this issue. Chris ----Original Message---From: John Baumgartner Sent: Tuesday,
October 26, 19997:55 AM To: Lea Dunn Cc: Chris Teny Subject: RE: Lea, It is my understanding that traffic issues related to the modem roundabout located at Quorum Drive and Addison Circle
are being addressed by Chris Teny. Please let me know if I can be of any further assistance. Thank you, you, John --Original Message-From; "Lea Dunn " Sent: Monday, October 25, 19992:45
PM To: John Baumgartner Co: Chris Teny Subject: FW: 
􀀱John If you are the appropriate person, would you please respond to this person. If not, let me know who I should direct this inquiry to. Thanks, Lea --Original Message-􀀧􀁾􀀺􀀮􀁲􀀺􀁩􀁬􀀻􀀻􀁾􀀻􀁩􀁴
􀀻􀁾􀁾􀀺􀁮􀀡􀁾􀁴􀀡􀀻􀁾􀀱􀁾􀁾􀁦􀀺􀀺􀁾􀁾􀁾􀁡􀁮􀁯􀀧􀁢􀀧􀁃􀁏􀁦􀁵􀁪􀀧􀂷􀁆􀁾􀁾􀁩􀀻􀀻􀀷􀀡􀀻􀁥􀀬􀀧􀀮􀁯􀀻􀀻􀀻􀀻􀀡􀀺􀀺􀀻􀁩􀁻􀀮􀁊􀀧􀁾􀂷􀂷􀀻􀀬􀀬􀀻􀂥􀀻􀀻􀀻􀀧􀀻􀀠 To: Idunn@cLaddison.tx.us Subject:
Hi, I recently started to drive down Quorum Dr. through Addison, to get to my new job on Beltline Rd. On two separate occasions, I've nearty been struck by vehicles whipping around the
Addison traffic circle. This traffic circle Is extremely dangerous and something must be done, before someone gets hurtl I would like to recommend installing stop signs at all entry
points to the traffic circle. This would at least slow people down, before entering the circle. Could you please pass this along to the right parties? Addison is my most favorite place
in the whole Metroplex! Thank You, Mike Santamaria (972) 982-49721work m santa@yahoo.com Do You Yahool? Bid and sell for free at http://auctions.yahoo.com 
nv\V. IV URlVEA ROUNDABOUT Other Traffic Information ., t l '! "<,"",<J" ' brochures available: 
􀁀􀁩􀀺􀁩􀁲􀁹􀁾􀁡􀁬􀁬􀁭􀁧􀁾􀁲􀁦􀁲􀁩􀀸􀁦􀁩􀀻􀀧􀀻􀀬􀀧􀁾􀀬􀀠},:" ' From: Ron Whitehead Sent: Friday, July 30, 1999 4:44 PM To: John Baumgartner; Chris Terry Cc: Lea Dunn Subject: RE: Complaint
-Speed bumps at Addison Circle -----Oliglnol Messagec---From: John Baumgartner Sent: FrIday, July 30, 1999 4:31 PM To: ChriS Terry; Ron Whitehead Ce: Lea Dunn Subject: fW: Complaint
-Speed bumps at Addison Circle John, No, I want to see' how it works when the development surrounding the circle is in place first. Also, we need to see what effect the sculpture has.
I think it is too early. In the spring we can reevaluate. 'We might want to place other traffiC calming devices out there or an occessional stop sign. Ron Do you want to have our consultant
(Huitt-Zollars) evaluate this request and make a recommendation? 􀁆􀁲􀀻􀀮􀁳􀁲􀁩􀁾􀁩􀁾􀁾􀁉􀁌􀁾􀁗􀁾􀁾􀁾􀁾􀀠'i. ". Sent: 'Friday: Jl.lly 30,1999"2:26 PM . To: John Baumgartner Subject:
FW: Complaint -Speed bumps at Addison Circle I ' John, Chief Padden forwarded this information to me. Would you please follow up with Ms. Newsom regarding her request. Thanks, Lea -Original
Message---From: Gordon Robbins Sent! FrIday, July 30, 1999 9:01 AM To: NoelPaddan Subject: Complaint -Speed bumps at Addison arcle I recently was asked by a shop owner at Addison Circle
(Andra Newsom of TRENDS) whether or not the Town could install speedbumps on Quorum at the entrances to the traffic circle. Apparently some drivers think it quite sporting to accelerate
into the circle and see how fast they can take the' curve (I'm sure none of these people are Audi drivers). Andra says this wasn't too much of a problem until people started moving into
Phase 2. But now that we have over 420 apartments occupied on the other side of Quorum, more and more people are crossing the street each day and the potential for a problem is much
greater. 
Anyhow, I wanted to forward this complaint through channels to the proper parties. Please let me know if you have questions. -Gordo 
--, ,; ,I 1 1 MODERN ROUNDABOUT -) for ADDISON CIRCLE November, 1995 I Revised March 1, 1996 I,, 1 i Prepared By: i I ; Andrew C. Oakley, P.E. Huitt-Zollars, Inc. I ) 3131 McKinney Ave.,
Suite 600 Dallas, TX 75204 (214) 871-3311 in association with Peter Doctors, P.E. --, Ourston & Doctors -1 5290 Overpass Road, Suite 212 J Santa Barbara, CA 93111 .'" (805) 683-1383
􀁽􀁾􀀺􀀠I ) ,.:;t 1, Prepared For: .) -) The Town of Addison J and Columbus Realty Trust , _J I -. 
ADDISON cmCLE MODERN ROUNDABOUT ANALYSIS MARCH 1, 1996 INTRODUCTION This report was prepared for Columbus Realty Trust and the Town of Addison as supporting documentation for the design
of a "modern roundabout" at the intersection ofQuorum Drive and Mildred Street within the special zoning district known as "Addison Circle". The report was prepared by Peter Doctors,
P.E., of the fl11l1 of Ourston and Doctors, modem roundabout consultants based in Santa Barbara, California under the direct supervision of Andrew C. Oakley, P .E., of Huitt-ZoUars,
Inc., Dallas, Texas, Who also edited and contributed to the text. BACKGROUNDIROUNDABOUT OPERATION The term "modern roundabout" refers to a type of traffic circle with very special characteristics
of geometry and operation. The concept of the modern roundabout to replace the conventional traffic circle came about in an attempt to overcome the operational failure that occurs when
there is so much traffic in the circle that gridlock occurs. A modern roundabout operates on a simple principle already familiar to drivers, the one way street. The principle uses two
signs, the YIELD sign and the ONE WAY sign. A circular roadway is constructed with roads entering like spokes on a wheel. The circular road is one-way with the entering roads yielding
to circulating traffic. When a driver approaches the roundabout, he/she looks to the left to see if anyone is in the circle and if empty, enters the circle. If someone is in the circle,
the entering driver waits for an appropriate gap in traffic and then enters. Once in the circle the driver has the right of way and exits the circle when arriving at their chosen road.
The primary differences between a modem roundabout and a traditional traffic circle are as follows: • In a roundabout, approaching traffic yields to traffic already in the roundabout
whereas, in many traffic circles, entering traffic has the right of way. A car approaching the roundabout looks to the left at circulating traffic and determines if a gap is available
to 1 
enter the roundabout safely. If there is not a gap available in the circulating traffic stream, the driver waits at the yield limit line until a gap is available. The location of the
yield limit line, the presence of a yield sign and the deflection of the vehicle's path upon entering the roundabout contribute to making this a simple decision process. • Traffic entering
a roundabout is deflected around the roundabout by geometric features of both the approach road and the central island. By providing this deflection, the vehicle speeds are reduced,
making decisions for the driver easier as well as increasing the safety of the intersection. The roundabout is the safest form of intersection and the deflection requirements contribute
to this element of safety. • Approach roads are widened as they near the roundabout to increase their capacity. This widening is referred to as "flare". The flare length is much shorter
than a standard intersection widening. In fact, flare lengths over 80 feet do not provide any significant increases in capacity. The flare lengths used in the design provide for adequate
capacity without extensive widening of the approaching roadways. BASIS FOR DESIGN Design parameters for the modern roundabout have been developed empirically in Europe and Australia
over the last 30 years. In the last several years, modern roundabouts have gained usage in the United States. Experimentation with various combinations of entry width, approach width,
entry radius, entry angle and inscribed circle diameter have led to optimum operation under variable conditions. As a result, computer programs have been developed which allow the input
of traffic data and geometric characteristics with resulting output of average delays relating, in turn, to level of service. Ourston and Doctors roundabout designs follow technical
advice by the British Department of Transport. The designs of all the modern roundabouts built to date in California, Nevada, Maryland, and Colorado also follow British design advice
and they operate well with little delay and few accidents. 2 
Traffic performance estimates for the Addison Circle Roundabout were made using the computer application RODEL. RODEL is bused on research by the Transportation Research Laboratory in
the United Kingdom. Approximately SSM was spent on collecting data at 86 different roundabouts. From this data, equations linking the various geometric parameters were developed and
applied in the computer application ARCADY and RODEL. This program estimates average vehicle delay for each approach to the roundabout. The program has been used to analyze roundabouts
in California, both in Long Beach and Santa Barbara, with delay estimates of RODEL deviating from observed delay by no more than two seconds. TRAFFIC ANALYSIS Analysis of the proposed
modern roundabout at the intersection of Quorum Drive and Mildred Street was based on the following facts and assumptions about these roadways. • Quorum Drive is a 4-lane divided roadway
with recessed parallel parking lanes to be added to both sides. • Mildred Street, though technically technically wide enough to be 4 lanes, is assumed to be a 2-lane undivided roadway
with parallel parking on each side. (However, approaching the roundabout, a center island is introduced and parking is eliminated consistent with standard. design practice). • ADT for
Quorum Drive at buildout will be 30,000 VPD and ADT for Mildred Street will be 10,000 VPD. The directional distribution ofpost-development peak hour travel routes and the volume of traffic
that would be making each turning movement during the peak hours were both needed in order to design the roundabout. The volumes and distribution that were used to design the roundabout
for Addison were arrived at based on the following assumptions: 3 
• Only those tracts that face Quorum Drive and/or Mildred Street will be developed into anything other than multi-family residential uses. • Based on the proposed land use mix for Phase
I, 7% of the floor area proposed for each mixed-use tract will be developed into non-residential uses. • The relationship between the number of dwelling units developed on a particular
tract and the amount ofavailable floor area on that tract will be similar throughout the residential subdistrict. Based on our understanding that a total of 5,050 multi-family dwelling
units are proposed for the residential subdistrict, and the three assumptions just described, the number of dwelling units that will ultimately occupy each tract could be calculated.
A map of the proposed district indicating the various development tracts is presented in Figure I a. The results of the calculation process are presented in Figure lb. Using trip rate
information contained within the ITE Trip Generation manual and the San Diego Association of Governments Not So BriefGuide ofVehicular Traffic Generation Rates ofthe San Diego Region,
daily and peak hour trip rates were calculated for each tract. The results are presented in Figure 2. During the peak hours, site-generated traffic will be distributed about the surrounding
roadway network as follows: • 15% of site generated traffic will be traveling to or arriving from the north. • 30% of site generated traffic will be traveling to or arriving from the
south. • 35% of site generated traffic will be traveling to or arriving from the east. • 20% of site generated traffiC will be traveling to or arriving from the west. Based on this distribution,
peak hour site traffic was assigned to the adjacent roadways. Then, based on the "at buildout" daily traffic volumes expected on Quorum Drive as dictated by the 4 
--I COMMERCIAL SUIIDIlITRICT U¥f Jil'fNARYUSE OI! A 􀁾OF PRIMARY uS£S """ ,..... 􀁾􀀮􀀠 '''"'"' " """"""' I:m ,., '.n ..• --..:1-_--........... ''.k'11_0 -..:r ___ ...VARIATIONS/ALTERATIONS
DRAFT 2􀁬.. 􀀮_􀁖d􀁬􀀻_􀁩t􀀮o􀁦r􀀯e􀁉,􀁉p􀁟􀀢."􀀢􀀧"􀁟 _􀁾􀀬___ ............__IDr_.......-__. 􀁾􀀭􀀭􀀭..-............. .. __􀀧􀀱􀀱􀀱􀁾__ 􀀮􀁜􀀮􀀮􀁟􀀭􀀭􀁾􀀢􀀧􀀭. [ r _ to."...L 􀁾 ..
-..-. ..􀁾􀀢􀀢_􀀢_􀀧_􀀪 􀀢􀀧􀀭 i IHnt1!5 (:()MtIIERCl.U. 􀁾OFTHE U.C. OISTMICTl ... .... ,m -'" • 􀁾􀀠 ------• RESIDENTIAL SUBDISTRICT •-I.n .n.... (A"""OF 1500 FIE$IlEN'TW. UoIITS 1'0
OCCUR .. "1.H U. ....,---, I.U -..,.--'\M'IM!N PMASa eta:: AND two) ,., 􀁾􀀠 -....... '.n -----.......... 􀀭_􀀮_􀀮_􀀬...J 􀀭􀁾􀀭􀀭 ...""--U 1,14 􀀮􀀬􀁾􀀧􀀢 .,... ... ___1_,'M... --.-.,------....,.,
-.. 0.7;: -,..".'" ,.. ----,• 􀁾􀀠 .M .. __ "1_---..........,. 'M __.,,/WG_ 􀁾􀀱􀀬􀁦􀁏􀁉􀁉􀀠 􀁾􀀠 . PUBtJC OPEN SPACE .. ". __ _Ml_WJ wt____ _____ .. ... ..,""" 'No,ne -..,---• ......".,I.....
--""-'• 􀀮􀀮􀀬􀁬􀁍􀁬􀀮􀀬􀁾􀀭􀀡􀁴􀁑􀀮􀁟􀀡􀀢􀀨...1. '-U..O.....l.,....1I1•􀀮􀀬􀀬􀁾􀁉􀁉􀁉􀁉􀁉􀁉􀁍􀀩􀀮􀀴􀀬􀀮􀀬􀀮􀀮􀁩..􀀺􀁾...1;4 FIGURE 1a ...􀀢􀀢􀀧􀀢􀂻􀁡􀀻􀁾􀁟􀀮􀀮􀀬􀀬􀀮...._flb..􀀢􀁬􀁗􀁯􀀻􀁓􀁎􀁣􀁾􀂷
PRELIMINARY CONCEPT PLAN 􀁾􀀠'''' C;III....loIIIMMIII'MI; .. Ii,..U••.,,......, • .,...,,,r.w. • Salle: /.=100' _'-IWl.."",.,.,.,..as.......lM......1f;.JfI1 􀁾 . Addison Urban Center.
􀁾􀀠 "-"'''. ADl il"O:\ Special Distri<.:t Planning • Addison.Texas II/AI h"" "," -ill< 
I-A 144,500.00 1-8 130,750.00 l-C 150,900.00 ! ! 2-D 176,550.00 167,500.00 2-1( 518,650.00 2-L 290,300.00 2-M 206,800.00 2-N 413,800.00 2-0 565,800.00 2-P 393,800.00 3-F 284,000.00 i
3-0 286,600.00 I 3-H 351,900.00 3-1 321,250.00 3-J 186,750.00 I TOTALS 4,589,850.00 10,155.00 9,153.00 10.563.00 0.00 0.00 0.00 20,321.00 14,476.00 28.966.00 39.606.00 27,566.00 0.00
0.00 I 24,633.00 I 321.250.00 186,750.00 693,399.00 134,385.00 121,597.00 140,337.00 176,550.00 I 167,500.00 518.650.00 269.979.00 192.324.00 38·U34.00 526.194.00 I 366.134.00 I 284.000.00
286.600.00 327,267.00 298,762.00 I 186.750.00 4,381,963.00 I 3.07 155.00 2.77 140.00 3.20 162.00 4.03 204.00 I: 3.82 193.00 11.84 596.00 6.16 311.00 4.39 222.00 8.78 ..;..44.00 12.01
8.36 4'22.00 I 6 . .18 327.00 6.54 330.00 1.47 377.00 6.82 34-1.00 4.26 215.00 100.00 i 5,050.00 As specified 011 Preliminary Concept Plan Assumed, based all PrelJmi=y Concept Plan FIGURE
1b Assumed Land Use Mix By Tract """----------_HUITI-lOLIARS 
ADDISON CIRCLE MOl)J::}{N KUUNUflliUUT 􀁁􀁎􀁁􀁌􀁙􀁾􀁬􀁾􀀠 ! • 􀁾􀁾••􀁾􀁷􀀠 tJ:tf 􀀭􀀺􀀺􀀬􀁾 􀁾􀁾􀀺􀁾􀀨􀀩􀁾􀀦􀀠 ;"TlUl'!>C " 􀁾􀀬􀀠. ,,':" , ' ,,,:c,.: 􀁾􀀻,..•􀀺.•􀀺.,􀀠 ' ".' '>:. i',
•DAlI.Y .. ·'iJU'..f.:: P£AK. P;.";f; P£AK. .:,.... ". 0,': 􀁾􀁾􀁾􀀻􀀡􀁾􀁲􀀡􀁾􀁉􀁦􀁪􀁧􀀧􀀻􀁲􀀮􀁾􀁪􀁩􀁾􀁾􀁾􀀧􀀺􀁾􀀠Ft Ig::""Y":: _I.:'''':.''> , ,{:'::'" 􀀱􀀸􀀺􀁾􀁕􀀧􀀾􀀱􀀧􀀺􀀺􀁾􀀧􀀯􀀺􀀾􀀠
"' :, " I-A 1 10,115 155 loB 9,153 i 140 I I-C 10,563 162 2-D 0 204 2..E 0 193 2-K 0 596 2·L 20,321 311 1 2-M 1 14,476 I 􀁾􀀠 2-N 28,966 44'! 2-0 39,606 608 2-P 27.566 421 3-F 0 327
1 3-G 0 330 3-H I 24,633 37i 3-I 22,488 344 3-1 0 215 I TOTALS, 201,887 5,050 1.409 1.271 1.473 1,281 1.211 1.876 2,861 2,029 4.107 5,650 3.901 2.078 2,097 3.478 3,170 1.352 39,:244
I ':>HOUR'< , ,,'IN' ;' l Or)T' , 25 71 22 66 25 Ii 18 86 17 , 31 50 I 246 49 143 34 103 69 203 I 92 279 65 194 28 136 28 ml 58 I li4 52 159 19 i 90 651 2,24S HOUR' " ., ,.... IN' OuT
90 5.5 i 81 50 94 57 84 40 80 I 37 I, 227 107 • 173 108 126 78 243 I 150 : 327 204 232 144 , 131 61 I I , 131 62 208 129 191 118 88 421 2,506 1,4421 As specified 00 Prelimino.ry Concept
Plan Assumed, based on Preliminary Concep' Plan FIGURE 2 Expected Traffic Generation Rates By Tract 􀁾__________________􀁈􀁕􀁩􀁬􀁬􀁾􀁾􀀠
Town of Addison, and those expected on Mildred Street as predicted by Barton-Aschman Associates, Inc., along with traffic count data collected on Quorum Drive in 1995, background traffic
volumes were then added to the site generated volumes to create post-development traffic assignment models. These are presented on Figures 3 & 4 and are the basis for the design of the
roundabout. DESIGN ANALYSIS The project post-development volumes were entered into the RODEL model, as were iterative values for each of the five geometric parameters. The analysis was
performed based on achieving a Level of Service C or above. After several iterations, the model arrived at a roundabout with acceptable levels of service in both the AM and PM peak hours
based on a combination of geometric variables that created an acceptable urban pedestrian environment while also meeting the vehicular needs for roundabout operation. The primary elements
of the fmal recommended geometry are an inner curb radius of 67 feet; an outer curb radius radius of 100 feet; approximately 33 feet of flare (3 lanes) on the Quorum Drive approaches;
and approximately 23 feet of flare (2 lanes) on the Mildred Street approaches. This final geometry is illustrated in Figure 5 and with a greater level of detail on the construction plans
in Appendix A. The RODEL printouts indicating estimates of average delay on all legs are included herein as Figures 6 & 7. Geometric information IS shown in the upper left hand portion
of the RODEL printouts. Dimensions are in meters. The following symbol key is provided to interpret the variables. E Entry Width (the width of flare on approach) V Approach Width RAD
Entry Radius PIll Entry Angle DIA Inscribed Circle Diameter (the outer curb) Estimates of the average delay for all vehicles entering the roundabout are 22.2 seconds per vehicle for
the A.M. peak hour and 11.6 seconds per vehicle for the P.M. peak hour. These 5 
---ADDISON CIRCLE MODERN ROUNDABOUT ANALYSISn NORTH 􀁾􀀠 a ::E iiZ 5 o J􀁾\r"MILDRED STREET ------;:: 78 (23)[55J ,.,;If 302 (11)[51J. 118 (12)[ 48J 􀁾􀀠'tf LEGEND [99] SITE GENERATED
TRAFFIC VOLUMES (RESIDENTIAL) (99) SITE GENERATED TRAFFIC VOLUMES (NON-RESIDENTIAL) ........ [28J(3) 31 4 [96J(16) 272 iL"'" [123J(6) 129 RGURE3 A.M. Peak Hour Site Plus Background Traffic
Volumes HUITT-lOLlAPS ...9_99_S_ITE_PL_US_B_AC_KG_R_OU_N_DTRA_F_FIC_VO_l_UM_ES_,_______ 
__________________ ·'--ADDISON CIRCLE MODERN ROUNDABOUT ANALYSIS1 1 t<J r--\f)(j) 􀀭􀀺􀁴􀁜􀁦􀀩􀁾􀀠 􀀮􀀮􀀭􀁾􀁾􀀠 3!: -OS' 􀁾􀀠(j) -:t '-" t<J 􀁾􀀠 :::E e'-n" a􀁾 ;a::: :; 􀀺􀀺􀀺􀁬􀀨􀁪􀀩􀁃􀁜􀁊􀁾􀀠
􀁾􀀠 '--' '--' '--' ___􀀭􀀺􀀺􀀺􀁾􀀠J􀁾\, 303 (53)[250] ""JIf 219 (33)[63J 􀁾􀀠 80 (26)[54].... \'tf LEGEND [99] SITE GENERATED TRAFFIC VOLUMES (RESIDENTIAL) (99) SITE GENERATED TRAFFIC
VOLUMES(NON-RESIDENTlAL) 999 SITE fLUS BACKGROUND TRAFFIC VOLUMES 􀁾􀀠 n NORTH MILDRED STREET "-[19](7) 26 • [63](33) 279 Itt"'" [68J(51) 119 HGURE4 P.M. Peak Hour Site Plus Background
Traffic Volumes 􀁈􀁵􀁲􀁲􀁲􀁩􀁄􀁾􀀠
.......::;:::::::::..:-: :.:-............... ""'" .. .... ". I I I I I I "". EO 51 􀀧􀀮􀁾􀀮􀀠," MI\..OR ........ ' ,." .... .,., ..... " ..-" Scale: 1"=80' ..' ..' ....: Ourston & Doctors
ADDISON ROUNDABOUT MODERN ROUNDABOUT INTERCHANGES Addison Circle 5290 Overpass Road #212 Santa Barbara, CA 93111 FIGURE 5 
• • • • • , t t 10:10:95 ADDISON ROUNDABOUT 15 • t , 􀁩􀁩􀁊􀁬􀁩􀁴􀁩􀁩􀀪􀀪􀁩􀁴􀁴􀀨􀁊􀁃􀀻􀁴􀁩􀁩􀁩􀁾􀁩􀁬􀁾􀁴􀁴􀁴􀁴􀁴􀁾􀁴􀁴􀁴􀁴􀁴􀁴􀁴􀁴􀁴􀁩􀁬􀁴􀁴􀁴􀁴􀁴􀁴􀁴􀁴􀁩􀁴􀁴􀀻􀁴􀁴􀀥 􀁴􀁩􀁴􀁴􀁩􀁬􀁴􀁬􀀱􀀱􀀱􀁴􀀡􀁩􀁬�
� , j 3 , , , E (Q I 10.00 U2 10.00 1.32 , 1[HE PERIOO 􀁾􀁩􀁮􀀠 90 I , l' (m) 16.43 14.13 16.60 22.13 I fiNE SLICE lin 15 I , V (m) 7.01 UZ 1.01 4.12 , RESULlS PERIOD 􀁾􀁩􀁮􀀠 15 75
, S",(".,--"):>, RRD 􀀨􀁾􀀠) 39.63 18.29 36.58 45.73 ' lIHE COST 􀁯􀀯􀁾􀁩􀁮􀀠 U9 , , , PKI (di 27.00 57.00 30.00 27.00 • flOW PERIOD lill IS 15 , , DIR 􀀨􀁾􀁬􀀠 60.98 60.98 60.98 00.98
' fLOK TYPE oeuiven VEH ,, G RRD SEP 0 0 0 0 t 􀁦􀁬􀁏􀁾􀀠PEA! 31100101 AM ,I t:titU:UUttUUUUUt:tUiiUiUUiturttttt::UtUfUtfU:t:U.UUtUtUtUUUtl ,, LEG NRME ,'P CU ,If LO WS (1st exit 2nd
ete...UI,'f lOF,'c L' flOW RAllO 'fLOK T!MEt I , I 􀁾􀀠 'NS QUORUH '1.0S' 83 385 70 0 '1.00185'0.15 [.125 0.75'15 l5 IS ' 'KB HILOREOtl.OS' 31 272 129 0 '1.00'85'0.75 1.125 0.75'[5 ,5
75 ' '58 QUORUH '1.05' m 1014 304 0 '1.00'85'0.75 1.1250.75'(5 45 15 , ,'E 8 HILDREO'I.OS,' Il8 302 78 0 '1.00,'8 5',0 .75 1.1250.75'15 l5 75 ,, , t • , • t , t , , , • , , , fLO. veh
601 483 1783 556 I TOTAL OELRYS , CAPACm veh 1848 IIII 1982 763 • • , L........\ of --'!I> ' RVE DElAY .ins 0.05 0.09 0.55 US 21 hrs t 1􀁅􀁲􀀢􀁖􀁜􀀨􀁾.. c:... • MAX OElRY "ins 0.00 0.13
1.22 0.13 I • RVE QUEUE veh 0 I 11 4 • 99 oounds ' •, H AX QUEUE ven 1 35 6 , A.M. Peak Hour FIGURE 6 
• • • • • • • • * 10:10:95 ADDISON ROUnDABOUT 40 • 􀀺􀀻􀀪􀀪􀁩􀁩􀁩􀀪􀁩􀀪􀀻􀀪􀀪􀀼􀀺􀁩􀀩􀁴􀀪􀀪􀀪􀁾􀀪􀀪􀀪􀁾􀀪􀀪􀀪􀁾􀁩􀀪􀀪􀀪􀀪􀀪􀀪􀀪􀀪􀀪􀀪􀀺􀀪􀀪􀀪􀀪􀀪􀀪􀀪􀀪􀁩􀁩􀀪􀁴􀁴􀁴􀀪 􀁩􀁩􀁴􀁴􀁩􀁴􀀻􀁩􀁩􀁩􀀻􀁩􀀻􀀺􀀠
I: E 1m 1 10.06 1.J2 10.06 1.32 • TlHE PERIOD ain 90 • • L' (I) 11i.43 IU3 16.60 22.13 • TINE SLICE 111 n 15 • * V (m) 1.01 4.12 1.01 4.12 • RESULIS PERIOD .in 15 15 * T ..... r........
-7 * RAD lm) JUJ 18.29 J6.58 45.13 • flHE COST p/.in 1.19 • * PHi (d) 21.00 51.00 30.00 27.00 , nOM PERIOD min 15 15 * * DIA (m) 60.98 60.98 60.98 􀀶􀀰􀀮􀁾􀀸􀀠 • FlON rYPE pcu/veh VEH
• • GRAD SEP 0 0 0 0 ,• fLOM PEAK .o/oo/pi PH • * * t***'****tii*i*i*ii***i*;t;ti,*ti*i*i*i*t*ti*i*t**;t,;t,t'i;li;;;;;'i;t,!;t;i;;; • LEG NAME 'PCU 'fLOWS (1st exil 2nd etc •.. UI*fLOF'CL*,
nON RATIO *now fiNE' i * * * • I * * 'NS QUORUM *1.05'10 1099 S6 0 '1.00'65*0.151.1250.75*1545 75 • 'W8 HILDRED'I.OS' 26 Z79 119 0 '1.00'85'0.15 1.125 0.15'15 45 15 • 'S8 QUORUM '1.05' 147 553 169 0 '1.00'85'0.75 1.1250.75*154575 • ,'E
B HILDRED'I.05,' 80 219 303 303 0 '1.00'85'0.751.1250.15'154515 • * • • , • •• • • • , • , • • * • • * • • • • flOW yeh 1402 m 9lI • CAPACITY yeh 1843 625 1m L"-J..,\ .f '"""'? • AVE
DELAY ains 0.1& 0.65 0.0& 􀁾􀁾􀁎􀁬􀀨􀀮􀁥􀀮􀀮􀀠 • MAX OELAY tins US U3 0.08 * AVE QUEUE yah 4 S I • MAX QUEUE veh 6 10 I • 672 11&2 0.13 0.19 1 2 * TOTAL DELAYS • * • , •II hrs • •• 53
pounds' * • P.M. Peak Hour FIGURE 7 
delays equate to Level of Service C and B during the AM and PM peak traffic hours, respectively. Level of Service C corresponds with 16 to 30 seconds of delay per vehicle. Calculations
are shown on the attached Roundabout Level of Service worksheet, Figure 8. Capacity and delay estimates are made at the 85-percent confidence level. These estimates are conservative
compared to capacity and delay estimates for signalized intersections in the United States, which are made at the 50-percent confidence level. FINAL DESIGN AND CONSTRUCTION DRAWINGS
The traffic analysis for design of a modem roundabout results in the horizontal geometry of the circle itself and its approaches. There are, however, many other consideration and design
elements necessary to produce a complete, functional roadway. These include vertical geometry, including profiles and typical sections; drainage; pedestrian circulation; relationships
to on-street parking; lighting; signage; markings; and landscape limitations. The basis for design of these elements is explained in the following paragraphs and the results for the
Addison Circle Roundabout are illustrated on a partial set of reduced construction drawings which are included herein as Appendix A. Grading. Drainage and Roadway Profile A unique design
approach to the vertical geometry of a modem roundabout has been developed to provide a safe comfortable driving experience and to facilitate the traffic movements that occur through
the circle. The base element of the design is an imaginary line one-third of the way between the outer curb and the inner curb. For the Addison Circle Roundabout this distance is 11
feet. The profile of this baseline (or "centerline") is a single phase of a cosine curve whose apex is usually set at the point of the highest entering roadway and whose nadir is 1800
away. For the Addison Circle Roundabout, the base line is the invert of the street with a reverse parabolic crown approximating a straight crown of 2%. (See Figure 9) The physical centerline
ofthe travel lanes ofeach of the entering and exiting roadways is merged 6 
RGURE8 ROUNDABOUT LEVELS OF SERVICE 10·10·95 Ourslon & Doctors Addison Roundabout Projected Design Flows fl.M. PEAK HQUR VVHOLE LEG 1 LEG 2 LEG 3 LEG 4 LEG 5 LEG 6 ROUNDABOUT INPUT FRQM
RQQEL QR 􀁁􀁒􀁑􀁾􀁢􀀯􀁙􀀠 FLOW veh/hr 601 483 1783 556 3,423 AVE DELAY min/veh 0.05 0.09 0.55 0.38 QllIPUT AVE DELAY sec/veh 3.0 5.4 33.0 22.8 DELAY sec/hr 1803 2608 58839 12677 75.927
AVE DELAY, sec/veh 22.2 LEVEL OF SERVICE C PM. PEAK HQUR VVHOLE LEG 1 LEG 2 LEG 3 LEG 4 LEG 5 LEG 6 ROUNDABOUT INPUT FROM RQDELOR ARQAb/Y FLOW veh/hr 1402 474 971 672 3.519 AVE DELAY
min/veh 0.16 0.65 0.06 0.13 QlITPlJI AVE DELAY sec/veh 9.6 39.0 3.6 7.8 DELAY sec/hr 13459 18486 3496 5242 40,682 AVE DELAY, sec/veh 11.6 LEVEL OF SERVICE B Level of Service FIGURE 8

with the cosine curve to create, in this case, 8 smooth profiles. The result is a roadway that helps guide the motorist around the circle with minimum undulation in the traveling surface
which would cause discomfort. Drainage is concentrated along the base line and may be collected by grate inlets as necessary or as desired to minimize flow depth and ponding. Pedestrian
Circulation All research from Europe and Australia suggests that pedestrians are safer at roundabouts than at signalized intersections. Lower pedestrian accident rates at roundabouts
have been attributed to three factors: (1) Traffic moves slowly, about 15 to 20 miles per hour at roundabouts of this size. (2) The pedestrian must look only one way before choosing
a large enough gap in traffic to assure a safe crossing. (3) The pedestrian's passage is broken into two stages; from the nearside wheelchair ramp to the refuge in the median island,
and from the median island to the farside wheelchair ramp. The recommended locations of the pedestrian crossings are shown in Figure 5, indicated by two concentric dotted circles. More
detailed information is shown on the construction drawings included herein. These locations comply with the recommended distance of between one and three car lengths from the yield line.
A break in the median or splitter island is used for barrierfree passage across the street. On-street Parking Locations The location of on-street parking must be considered so that it
does not impair the operation of the roadway or cause traffic to back up into the roundabout. For entering roadways the location of the parking should be limited to a minimum 20 foot
transition before the BCR (begin curb return) of the roundabout. For exiting roadways the location of the parking should start at a point no closer than 100 feet from the inscribed circle
diameter. This will allow adequate stopping 7 1 
sight distance and storage for waiting vehicles. Lighting Requirements Lighting columns should be arranged around the perimeter of the roundabout in a simple ring, with the lights equidistant
from the center and from each other. Lighting should extend at least 200 feet back along each exit road. Mounting height should be uniform throughout the intersection and not less than
any approach road. Minimum horizontal illuminance at the curblines should be 1.9 footcandles. The minimum illuminance required should be not less than the highest level of lighting for
any of the approach roads. (Final lighting plans are not included in Appendix A. Only pedestrian lights are shown at this time). Signing and Striping Requirements The approach to signing
and striping of a roundabout is similar to other major intersections. Advance guidance signs are provided to inform motorist of destinations before they enter the roundabout. Advance
warning signs, yield signs, one-way signs or chevron boards and splitter island guidance signs are also necessary for the roundabout to operate successfully. The nature of the advance
warning signs is somewhat unique to roundabouts and they are illustrated in detail in Appendix A. The striping required at a roundabouts consists of a yield legend and yield limit line.
The limit line is not found in the MUTeD, but must be used in a roundabout to indicate the location for the motorist to yield. Landscaping Limitations To provide adequate sight distance
as motorists make their way around the circle, significant landscaping and sculptural features in the central island of this roundabout should be confmed within a diameter of 70 feet.
In this area any landscaping or statue can be constructed of infmite elevation. The remaining 32 feet between this landscaping/statue area and the central island curb 8 1 
must be landscaped with some type of ground cover or low plant that will not obscure the driver's visibility around the circle. Landscaping of the medians or splitter islands should
be limited to a maximum height of 3.5 feet to allow drivers to see circulating traffic, with exceptions for carefully placed single-trunk trees, limbed up a minimum of 7 feet. CONCLUSIONS
The installation of a modem roundabout at the junction of Quorum Drive and Mildred Street will provide for a safe and efficient intersection. An acceptable level of service can be achieved
for the intersection without the necessity of a traffic signal even during the AM and PM peak hours. The roundabout will provide an aesthetic benefit to the co=unity through the creation
of a significant space for public art and will help foster the urban environment by reducing the speed of traffic that might otherwise be experienced on Quorum Drive, without a loss
in capacity. I 1 9 
I j 1 APPENDIX A ADDISON CIRCLE PHASE I MODERN ROUNDABOUT • GEOMETRIC PLAN • STREETSCAPE PLAN • ROUNDABOUT PROFILE • APPROACH PROFILES • SIGNAGE & STRIPING PLAN • TRAFFIC SIGN DETAILS
] ':j I J J j 􀁾􀀬􀀠I .J J 
HIli Uln UUI lUll UUl !...!. I:'I.I' nm nUl ""I ; NO. • 2,•••7••10 "12 I> fA 15 '6 I1.7 I. 20 ZI 22 Z3 .. 􀀲􀁾􀀠 2. 27 ClJRIIE A 6 e D E F G H I J•.. N H 0 p 0 R S T U V v•Y: .. A 􀁌􀀮􀁏􀁃􀁁􀁴􀁉􀁾􀀠
PRC 􀀡􀀵􀁾􀀹􀀮􀀱􀀧􀀠 AT, RP 3,01' RT. PRe O.Ot· LT 􀁾􀀠 PRe 6.1!5' L.L RfI 1..4:1' L. T, PRe 1.31' L.T. PRe 18.32" RT. 􀁾􀀠18.:11' RT, PRe 19.oi2" RT, PT 2,51' LT. PRC 0.61' LT. 􀁾􀀠to.l.('
LT. PRC 10.SS· LT. PRC 10.63' RL RP 11.30' RT. 'PRC 16.05' RT. PC 8.02' LT, PC B.II' RT, PRC 2.72' RT. PT 􀁾􀀮􀀹􀀷􀂷􀀠LT. PAC 16.63' LT. 􀁾􀀠IZ.OS' L.T. PRCII,A3'U. PAC 9.79' RT • RP
9.89' AT, PAC 10.82' RT. PT 1.13' RT. STA. J3+41.24 MILORED ST. STA. J3+41.88 MIL.OREe ST. STA. 13·41.82 MILORED ST. STA. 13+81.05 Mn.ORED ST* sTl.. 13+82..14 MILORED ST. StA. t3·81.7"
MILORED ST. SfA.. 􀁊􀀳􀀫􀁾􀀱􀀠MILDRED ST. STJ..13+88..$.l MILDRED ST. $TA.13+8B.12 MILOft£D ST. STJ.. f4+27..39 QUORUM tit STA. J3+7'2A7 QUORtJM DR. Sft... 13+'7'2..Oe OUOR\JM OR. STlI.•
13..11AS QUORUM !Ii. STA. 13*7Q.6& QUORUM OR. sTA. 􀀱􀀳􀀭􀀫􀀷􀁾􀀠QIJCIRtM OR. STA. 13+11'..Q9 QIJORlWI OR. STA. 1I+:!4.13 QUORUM OR. ST A. 􀀱􀀴􀁾􀁁􀁓􀀠OUORt..lM OR. STA. 1!i*I5.22 QUORUM
OR. STA. 􀁉􀁉􀀢􀁾􀁉􀁏􀀠0lJ0RUM tfl. STA. 11+71..24 OUORUM !Ii. STA. II+79.24 QUORUM OR. sU,,. 11+84020 QUORUM OR. STA. II"Ss..96 OUORUM OR. STA. 1,"SU1 OUORUM OR. 5TA. 11+82..57 QUORUM
OR. STA. 11+32..95 QUORUM tfl. QUORUM DRIVE CtJNt DATA DElTA R T L CO 1156"27'57' • 3.00' 2:1.28' 􀁡􀀬􀀧􀀱􀀲􀁾􀀠 !S.96' 18"31 􀁾􀀠19" IOS.OO· n.IZ" 33.94' 33.80' 110*39'21' • 􀁾􀀮􀁏􀁏􀀧􀀠
􀀱􀀮􀀲􀁾􀀧􀀠 􀀹􀁾􀀶􀀶􀀧􀀠 􀀸􀁾􀀲􀀲􀀧􀀠 12"04-'S" SW.OO· 9.!U' 19..81' 19.11' 125*35'00' , 􀁾􀀮􀁏􀁏􀀧􀀠 1.9!i' 2..19' 􀀱􀁾􀀷􀀸􀀧􀀠 􀁉􀁲􀂷􀀢􀀡􀀡􀀱􀁾􀁾􀂷􀂷􀀠 210.00' 21.6A· .c3.t3' 43.0!I"
18-45"00" rlo.oo· IS.. liS' 36.00' 35.84' Be·,S'A"· 1.00' 1.&7' 2.06' 1..72' 􀀱􀀲􀀭􀁓􀀹􀀧􀀡􀀵􀀸􀁾􀀧􀀠 94:.00' to..7t 􀁾􀀠 21 ..:53" 21.28" J r!l-';,e"G!!!" 5.00' 7 .9A" 10.09' e•.t&'
JI·."25+> 􀀱􀀵􀀰􀀮􀀰􀀰􀁾􀀠 1!S..S8' 30.61' 􀀳􀁏􀀮􀁾􀀧􀀠 fI· ..e·Ol u 􀀲􀀺􀀵􀁏􀀮􀀰􀀰􀁾􀀠 2S.IW' , 51.SO· 51.41' 11·46'!3H 250..00' 25.19' 51.39' 􀁾􀀱􀀮􀀳􀀰􀂷􀀠 "-!J8'30' 􀁾􀀠 .03.006
15.37' 30.'2" 30."0' 120·.... '27'· '.00' S.19' '0,.54:' 8.69' 12·:57 ,"" .. SW.OO· 10.88' 􀀲􀀱􀀮􀁚􀀷􀁾􀀠 21.22' J18·..􀁥􀁾􀀴􀀱􀀢􀀠 􀁊􀀮􀁏􀁏􀁾􀀠 1.69' 2.0T· 1.12' t7"S6""" J '!I.OO·
JS.US" 36.03' 􀁾􀀮􀀸􀀸􀂷􀀠 88·07'20·" :.00' I.'" 3.08' 2."" 8:r"!6'3I" 2 ..00' 1.72· 2.84# 2.61' 8tI·"3'O!!IH 2.00' 1.82' 2.96' 2.70' H"41".tSH 2.00' 2.25· 3.38' 2.99' 􀁏􀁬􀂷􀁉􀀻􀀨􀂷􀀲􀀶􀀧􀁾􀀠
110.00' 3.11' 6.22' 6.22' 􀁓􀁇􀂷􀀲􀀰􀂷􀁏􀁴􀀭􀁾􀀠 2.00' 1..8$' 3.0J· 2.14' 128·"0'2:0'" 􀀲􀀺􀁾􀀰􀀰􀁾􀀠 ".16' .....9· 3.,&r· 90",59:'"" 2 ..00· 2.02" 3.17' :.85' 􀀸􀀱􀀢􀀡􀁊􀀶􀀧􀀱􀁩􀀵􀁾􀀠•
􀀲􀀮􀁏􀁏􀁾􀀠 I 􀁾􀀠􀀷􀀴􀁾􀀠 2.86' 2..52' 00.',)2-01 H t 􀀱􀀧􀁾􀁏􀁏􀁾􀀠 0.5<' 1.074 I.OT' TOW'); or ADDISON SP£CLU.. EVD.'TS AAU j=-4r40'3Z" R" 􀁉􀁾􀀮􀁏􀁏􀀧􀀠 Lo; 124.81' T= 65.28' W
"t21.2!s' 􀁆􀁕􀀧􀁉􀀧􀁏􀁕􀁾􀀠 \ \ •••••r 􀁾􀀠 I { I m n•p, NO. 28 Z9 '0,,""".. ,. ,l"8. '0 AI 􀁓􀁬􀁁􀁔􀁲􀁾􀀠& OFFSET LOCATION PRC 2.8" LT. I' PT O,TZ' LT, PC 8.2l· RT, 1 PAC 10.01' AT
'j PC 0.4.' LT. PAC 2.29' LT. PC: 1.le' RT. PT 9.32' RT, PRC S.69' LT, PC 6.76' LT. PT o.cr.s· AT. PRC 2.09' RT. PC 0.26' LT. PRe 1.69' RT. DESCRIPTION sa. 14.07.39 su.. '''h09.19 Su..
'''hOB.60 STA.14·06,79 ST A. 14.19020 STA.14·21.16 ST A. 14+ 18.&4 STA. 14+20.71 STA.II+47.89 ST A. "+46.12 STA. 11+4:1.9:1 STA.II+47.71 STt... 􀁴􀁉􀀫􀀳􀁾􀁋􀀠 STA. fl+M.a2 ( DR. 00.
DR. DR. DR. DR. DR. DR. 00. DR. Oft. &'i: Oft. 􀀬􀁾􀁾􀁾􀀭􀀭􀁩􀁮􀀠 i􀁾􀀠I􀁾􀀠 MAP LEGEND 􀁅􀁬􀀮􀁾􀁔􀁒􀁉􀀻􀀻􀀺􀀠-01<o 1.10Hl PO\,{ w'e. 􀁾 f'I1£ f-Qn' IfIIIt lEU T!LEPHOtIE -,"'" • 1E\..tPM01t1£
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Modern Roundabout for Addison Circle November, 1995 Prepared by Peter Doctors, P.E. Andy Oakley, P.E. Ourston & Doctors Huitt-Zollars 5290 Overpass Road, Suite 212 3131 McKinney Avenue,
Suite 600 Santa Barbara, CA 93111 Dallas, TX 75204 
ADDISON CIRCLE MODERN ROUNDABOUT ANALYSIS NOV. 8, 1995 Introduction This report was prepared for Columbus Realty Trust and the Town of Addison as supporting documentation for the design
of a "modern roundabout" at the intersection of Quorum Drive and Mildred Street within the special zoning district known as "Addison Circle". The report was prepared by Peter Doctors,
P.E., of the firm of Ourston and Doctors, modern roundabout consultants based in Santa Barbara, California under the direct supervision of Andrew C. Oakley, P.E., of Huitt-Zollars, Inc.,
Dallas, Texas, who also edited and contributed to the text. Background/Roundabout Operation The term "modern roundabout" refers to a type of traffic circle with very special characteristics
of geometry and operation. The primary differences between a modern roundabout and a traditional traffic circle are as follows: In a roundabout approaching traffic yields to traffic
already in the roundabout. A car approaching the roundabout looks to the left at circulating traffic and determines if a gap is available to enter the roundabout safely. If there is
not a gap available in the circulating traffic stream, the driver waits at the yield limit line until a gap is available. The yield limit line, yield sign and the deflection of the vehicles
path upon entering the roundabout contribute to this simple decision process. Traffic entering a roundabout is deflected around the roundabout by geometric features of the both the approach
road and the central island. By providing this deflection, the vehicle speeds are reduced making decisions for the driver easier as well as increasing the 
safety of the intersection. The roundabout is the safest form of intersection and the deflection requirements provide for this safety. Approach roads flare on the approach to the roundabout
to allow increases in capacity. The flare length is much shorter than a standard intersection widening, with flare lengths over 80' not providing any significant increases in capacity.
The flare lengths used in the design provide for adequate capacity without unnecessary widening of the roadways. The concept of the modern roundabout to replace the conventional traffic
circle came about in an attempt to overcome the operational failure that occurs when there is so much traffic in the circle that gridlock occurs. A modern roundabout operates on a simple
principle already familiar to drivers, the one way street. The principle uses two signs, the YIELD sign and the ONE WAY sign. A circular roadway is constructed with roads entering like
spokes on a wheel. The circular road is one-way with the entering roads yielding to circulating traffic. When a driver approaches the roundabout, he/she looks to the left to see if anyone
is in the circle and if empty, enters the circle. If someone is in the circle, the entering driver waits for an appropriate gap in traffic and then enters. Once in the circle the driver
has the right of way and exits the circle when arriving at their chosen road. Basis For Design Design parameters for the modern roundabout have been developed empirically in Europe and
Australia over the last 30 years. In the last several years, modern roundabouts have gained usage in the United States. Experimentation with various combinations of entry width, approach
width, entry radius, entry angle and inscribed circle diameter has led to optimum operation under variable conditions. As a result, computer programs have been developed which allow
the input of traffic data and 2 
geometric characteristics with resulting output of average delays relating, in turn, to level of service. Our roundabout designs follow technical advice by the British Department of
Transport. The designs of all the modern roundabouts built in California, Nevada, Maryland, and Colorado also follow British design advice and they operate well with little delay and
few accidents. Traffic performance estimates for the Addison Circle Roundabout were made using the computer application RODEL. RODEl is based on research by the Transportation Research
laboratory in the United Kingdom. Approximately $8M was spent on collecting data at 86 different roundabouts. From this data, equations linking the various geometric parameters were
developed and applied in the computer application ARCADY and RODEL. This program estimates average vehicle delay for each approach to the roundabout. The program has been used to analyze
roundabouts in California, both in long Beach and Santa Barbara, with delay estimates of RODEl deviating from observed delay by no more than two seconds. Capacity Analysis The analysis
of the proposed modern roundabout at the intersection of Quorum Drive and Mildred Street was based on the following facts and assumptions about these roadways: • Quorum drive is a 4-lane
divided roadway. • Mildred Street, though technically wide enough to be 4 lanes, operates as a 2-lane undivided roadway_ Parallel parking will be permitted on both sides of the street,
except that, approaching the roundabout, where a center island is introduced, parking will be prohibited consistent with standard design practice. 3 
• ADT volumes on Quorum Drive and Mildred Street are expected to reach 30,000 VPD and 10,000 VPD, respectively, upon buildout of the proposed development. The directional distribution
of post-development peak hour travel routes and the volume of traffic that would be making each turning movement during the peak hours were both needed in order to design the roundabout.
The volumes and distribution that were used to design the roundabout for Addison were arrived at based on the following assumptions: • Only those tracts that face Quorum drive and/or
Mildred Street will be developed into anything other than multi-family residential uses. • Based on the proposed land use mix for Phase I, 7% of the floor area proposed for each mixed-use
tract will be developed into nonresidential uses. • The relationship between the number of dwelling units developed on a particular tract and the amount of available floor area on that
tract will be similar throughout the residential subdistrict. Based on our understanding that a a total of 5,050 multi-family dwelling units are proposed for the residential subdistrict,
and the three assumptions just identified above, the number of dwelling units that will ultimately occupy each tract could be calculated. The results of the calculation process are presented
in Figure 1. Using trip rate information contained within the Institute of Transportation Engineers Trio Generation manual and the San Diego Association of Governments Not So Brief Guide
to Vehicular Traffic Generation Rates for the San Diego Region, daily and peak hour trip rates were calculated for each tract. The results are presented in Figure 2. 4 
During the peak hours, site-generated traffic will be distributed about the surrounding roadway network as follows: • 15% of site generated traffic will be traveling to or arriving from
the north. • 30% of site generated traffic will be traveling to or arriving from the south. • 35% of site generated traffic wale be traveling to or arriving from the east. • 20% of site
generated traffic will be traveling to or arriving from the west. Based on this directional distribution, peak hour site traffic was assigned to the adjacent roadways. Then, based on
the "at buildout" daily traffic volumes expected on Quorum Drive, as dictated by the Town of Addison, and those expected on Mildred street, as predicted by Barton-Aschman Associates,
Inc.; along with traffic count data collected on Quorum Drive in 1995, background traffic volume projections were made for each individual turning movement. The projected background
volumes were then added to the site generated volumes to create post-development traffic assignment models. These are presented on Figures 3 & 4. The projected post-development volumes
were entered into the RODEl model, as were iterative values for each of five critical geometric parameters. Geometry was established and adjusted to reflect the following: • Space limitations
imposed by the proposed rig ht-of-way, proposed development and existing streets. • Spatial relationships dictated by good urban design following the Roundabout Design Guidelines. 5

• Past experience with roundabout characteristic similar to the Addison Circle conditions. After several iterations, the model arrived at a roundabout with acceptable levels of service
based on an acceptable combination of geometric variables. The final geometry is illustrated in Figure 5. The RODEl printouts indicating estimates of average delay on all legs are included
herein as Figures 6 & 7. Geometric information is shown in the upper left hand portion of the RODEl printouts. Dimensions are in meters. The following symbol key is provided to interpret
the variables. E Entry Width V Approach Width RAD Entry Radius PHI Entry Angle DIA Inscribed Circle Diameter Estimates of the average delay for all vehicles entering the roundabout are
22.2 seconds per vehicle for the A.M. peak hour and 11.6 seconds per vehicle for the P.M. peak hour. These delays equate to level of Service C and B during the AM and PM peak traffic
hours respectively. level of Service C corresponds with 16 to 30 seconds of delay per vehicle. Calculations are shown on the attached Roundabout level of Service worksheet, Figure 8.
Capacity and delay estimates are made at the 85-percent confidence level. These estimates are conservative compared to capacity and delay estimates for signalized intersections in the
United States, which are made at the 50-percent confidence level. 6 
Pedestrian Circulation All research from Europe and Australia suggests that pedestrians are safer at roundabouts than at signalized intersections. Lower pedestrian accident rates at
roundabouts have been attributed to three factors: (1 ) Traffic moves slowly, about 15 to 20 miles per hours at roundabouts of this size. (2) The pedestrian must look only one way before
choosing a largeenough gap in traffic to assure a safe crossing. (3) The pedestrian's passage is broken into two stages, from the nearside wheelchair ramp to the refuge in the median island, and from
the median island to the farside wheelchair ramp. The location of the pedestrian crossing is shown on the attached roundabout drawing, indicated by two concentric dotted circles. This
location complies with the recommended location of between one and three car lengths from the yield line. A break in the median will be necessary for pedestrian access with handicap
access if not at grade level. On-street parking Locations The location of on-street parking must be considered so that it does not impair the operation of the roadway or back up into
the roundabout. For entering roadways the location of the parking should be limited to a minimum 20 foot transition before the BeR (begin curb return) of the roundabout. For exiting
roadways the location of the parking should start at a point no closer than 100 feet from the inscribed circle diameter. This will allow adequate stopping sight distance and storage
for waiting vehicles. 7 
Lig htina Requirements Lighting columns should be arranged around the perimeter of the roundabout in a simple ring, with the lights equidistant from the center and from each other. Lighting
should extend at least 200 feet back along each exit road. Mounting height should be uniform throughout the intersection and not less than any approach road. Minimum horizontal illuminance
at the curblines should be 1.9 footcandles. The minimum illuminance required should be not less than the highest level of lighting for any of the approach roads. Signing and Striping
Requirements The approach to signing and striping of a roundabout is similar to other intersections. Advance guidance signs are provided to inform motorist of destinations before they
enter the roundabout. Advance warning signs, yield signs, one-way signs or chevron boards and splitter islands guidance signs are also necessary for the roundabout to operate successfully.
The striping required at a roundabout consists of a yield legend and yield limit line. The limit line is not found in the MUTeD, but must be used in a roundabout to indicate the location
for the motorist to yield. Landscaping Limitations To provide adequate sight distance as motorists make their way around the circle, significant landscaping and sculptural features in
the central island should be confined within a diameter of 70 feet. In this area any landscaping or statue can be constructed of infinite elevation. The remaining 32 feet between this
landscaping/statue area and the central island curb must be landscaped with some type of ground cover or low plant that will not obscure the driver's visibility around the circle. Landscaping
of the medians should be limited to a maximum height of 3.5' 8 
to allow drivers to see circulating traffic, with exceptions for carefully placed single-trunk trees, limbed up a minimum of 7 feet. Conclusion The installation of a roundabout at the
junction of Quorum Drive and Mildred Street will provide for a safe and efficient intersection. During the peak hours of the day, an acceptable level of service can be achieved for the
intersection without the necessity of a traffic signal. The roundabout will provide an aesthetic benefit to the community as well as reducing speeds adjacent to the roundabout. 9 
""-ADDISON CIRCLE MODERN ROUNDABOUT ANALYSIS""'" iii".,TOTAl; .• I" ,rTU,:' I,' ,,:, .< 􀁜􀀧􀁬􀁈􀁩􀀧􀁾􀂷􀀮􀀧􀀠 .: 1>:,4:111<A .1: "," ,CT.: !; :lSYlKAt.-l.: 􀁩􀁆􀁾􀁩􀀱􀀨􀁓􀁆􀀩􀀺􀀻􀀼􀀠
, (SF) I-A 144,500,00 10,155.00 1-B 130,750.00 9,153.00 l-C 150,900.00 10,563.00 2-D 176,550.00 0.00 2-11 167,500.00 0.00 2·K 518,650.00 0.00 2·L 290,300.00 20,321.00 2-M 206,800.00
14,476.00 2-N 413,800.00 28,966.00 2-0 565,800.00 39,606.00 2-P 393,800.00 27,566.00 3-F 284,000.00 0.00 3-G 286,600.00 0.00 3-H 351,900.00 24,633.00 3-I 321,250.00 321,250.00 3-1 186,750.00
186,750.00 TOTALS 4,589,850.00 693,399.00 • •• As specified on Preliminaxy Concept Plan Assumed, based on Preliminary Concept Plan RESIDENTIAL Ii' " '/NO. OF FLOOR.,: I'OFTOTAL :". DWELLING
A.,,1;,... ,r. UNITSH . ,': BY 􀁔􀀧􀀻􀁾􀀻􀀧􀀧􀀻􀀺􀀺􀀻􀀺􀀻􀀺􀀠 􀁾􀀻􀀠:....􀁾􀀠 .•.••. BY TRACT , . (SF) '(:.(, '0' I 134,385,00 3.07 155.00 121,597.00 2.77 140,00 ! 140,337.00 3.20 162.00
176,550.00 4.03 204.00 167,500.00 3.82 193.00 518,650.00 11.84 596.00 269,979.00 6.16 311.00 . 192,324,00 4.39 222.00 i 384,834.00 8.78 444.00 526,194.00 12.01 608.00 366,234.00 8.36
422.00 284,000,00 6.48 327.00 i 286,600.00 6.54 330,00 327,267.00 7.47 377.00 298,762.00 6.82 344.00 186,750.00 4.26 215.00 4,381,963.00 100.00 5,050.00 FIGURE 1 Assumed. Land Use Mix
By Tract -----------__HLIITT-ZOLlARS 
""-ADDISON CIRCLE MODERN ROUNDABOUT ANALYSIS----' * ** FIGURE 2 􀁩􀁦􀀷􀁩􀀲􀀬􀁾􀁾􀀺􀀬􀀠.!:, .';,,{l,_.c!,;) \lYNU. UI'". ;:,,' .􀀮:.....􀁩. 􀁬􀁦.􀁾i:: 􀂷􀀧􀁾􀁾 ;:r..:·;.:•. 􀀧􀁩􀀮􀂷􀀮􀀺􀀺􀀺􀁥􀀭􀁾􀁬􀀺�
�􀀧􀁬􀀻􀀺􀀧􀀮􀂷􀀺􀀧􀀻􀀻􀀠 􀀻􀀺􀀧􀁾􀀧􀀺􀁬􀀻􀁩􀁪􀀺􀀱􀀠 I-A 10,115 155 I-B 9,153 140 l-e 10,563 162 2·D 0 204 2·E 0 193 2-K 0 596 2-L 20,321 311 2·M 14,476 222 2·N 28,966 444 2-0 39,606
608 2·P 27,566 422 3-F 0 327 3-0 0 330 3-H 24,633 377 3-1 22,488 344 3-J 0 215 TOTALS 207,887 5,050 As specified on Preliminary Concept Plan Assumed, based on Preliminary Concept Plan
􀁩􀂷􀀮􀂷􀂷􀀮􀂷􀀺􀂷􀀮􀀨􀂷􀁾􀂷􀂷􀀻􀁲􀀻􀀺􀀧􀂷􀁩􀂷􀂷􀀻􀀧􀀺􀀺􀀺􀀻􀁾􀁩􀀻􀁴􀁾􀁾􀀺􀂷.•: 11:" ....·.i:ii,T....... .􀁾􀁾..ATEn ···{·nATf;y····· ;..;.,l. ". cr;AlI..··r P.Mt.PEAK 􀁰􀀿􀁾􀁾􀁾􀀧􀀠f;.;;';
.. ..........••.. .;HOUR· .... IN,·:.. ·•· .: our 1,409 71 90 55 1,271 22! 66 81 50 1,473 25 77 94 57 1,281 18 86 84 40 1,211 17 81 80 37 1,876 50 246 227 107 2,861 49 143 173 108 2,029
34 103 126 78 4,107 69 203 243 150 5,650 92 279 327 204 3,901 65 194 232 144 2,078 28 136 131 61 2,097 28 137 131 62 3,478 58 174 208 129 3,170 52 159 191 118 1,352 19 90 88 42 : 39,244
651 2,245 2,506 1,442 , I I Expected Traffic Generation Rates By Tract 1....-_________HlIlTT-lOLIAR5 
""-ADDISON CIRCLE MODERN ROUNDABOUT ANALYSIS---' n NORTH tt"t c(Jaa ..-..-1:<') N,-.,,-., UJ ........... N 􀁾􀀠 :> ..-I:<') N § 􀁾􀁾􀁾􀀠 􀁾􀀠 aac(J 􀁾􀀠􀁾􀁾􀁾􀀠 ___􀁾􀀦􀀠J􀁾\, MILDRED
STREET 78 (23)[55] .",J!f "'-[28J(3) 31 302 (11)[51J. 􀁾􀀠 [96J(16) 272 118 􀀨􀀱􀀲􀀩􀁛􀀴􀀸􀁝􀁾􀀠 It!"" [123J(6) 129 \tr FlGURE3 A.M. Peak Hour Site Plus Background LEGEND Traffic Volumes
[99J SITE GENERATED TRAFFIC VOLUMES (RESIDENTIAL) (99) SITE GENERATED TRAFFIC VOLUMES (NON-RESIDENTIAL) ..9_99_S_ITE_PL_US_El_AC_KG_R_OU_N_DT_RA_F_FIC_VO_L_UM_E_S________HUITT-ZOLlARS