Training tool-kit for vehicle conflict observations at intersections

Training tool-kit for vehicle conflict observations at intersections

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Training tool-kit for vehicle conflict observations at intersections
Florida -- Dept. of Transportation
University of South Florida -- Center for Urban Transportation Research
Place of Publication:
University of South Florida, Center for Urban Transportation Research
Publication Date:
Physical Description:
1 online resource (various foliations) : ill. ;


Subjects / Keywords:
Traffic surveys -- Handbooks, manuals, etc ( lcsh )
Traffic conflicts ( lcsh )
Roads -- Interchanges and intersections -- Safety measures ( lcsh )
non-fiction ( marcgt )


Prepared in cooperation with the Florida Dept. of Transportation and the U.S. Dept. of Transportation under contract nos.
General Note:
"April 1996."
Statement of Responsibility:
by the Center for Urban Transportation Research, University of South Florida ; prepared for the Florida Department of Transportation.

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Source Institution:
University of South Florida Library
Holding Location:
University of South Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
029179118 ( ALEPH )
754656787 ( OCLC )
C01-00236 ( USFLDC DOI )
c1.236 ( USFLDC Handle )

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Training tool-kit for vehicle conflict observations at intersections
h [electronic resource] /
by the Center for Urban Transportation Research, University of South Florida ; prepared for the Florida Department of Transportation.
[Tampa] :
b University of South Florida, Center for Urban Transportation Research,
1 online resource (various foliations) :
Prepared in cooperation with the Florida Dept. of Transportation and the U.S. Dept. of Transportation under contract nos.
WPI no. 0510721, state job no. 99700-7625-199, contract no. B-9079, and CUTR account no. 21-17-147-LO.
"April 1996."
Description based on print version record.
Traffic surveys
v Handbooks, manuals, etc.
Traffic conflicts.
x Interchanges and intersections
Safety measures.
1 710
Dept. of Transportation.
University of South Florida.
Center for Urban Transportation Research.
i Print version:
t Training tool-kit for vehicle conflict observations at intersections.
d [Tampa] : University of South Florida, Center for Urban Transportation Research, [1996]
w (OCoLC)34785479
Center for Urban Transportation Research Publications [USF].
4 856


TRAINING TOOL KIT FOR VEHICLE CONFLICT OBSERVATIONS AT INTERSECTIONS Prepared for the F lo r ida Department of T r ansportat ion By the Center for Urban Transportation Research University of South F lo r ida April 1996 This report has been p r epared in cooperation with the slate of Florida Department of Transportation and the U.S. Department of Transportation under WPI No. 0510721, State Job No. 99700-7625-199. Contract No. B-9079, and CUTR Account No. 21-17-147 -LO. The opinions, findings and conclusions expr essed in this publication are those of the author s and not necessarily those of the State of Florida Department ofTransportation or the U.S. Departme nt of T r ansportation.


TABLE S OF CONTENTS Page Purpose . . . . . . . . . . . . . . . . . . . . . . . . . 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . 1 Classroom Materials and Handouts ........ ...... ... .. ............. 2 Slides . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Video Tape .................................... ........... 4 Appendices A. Classroom Mat eria ls and Handouts . . . . . . . . . . . . 5 B. Slides ............. ...... ......................... 1 0 C. Video Tape .... ..................... ................ 12


PURPOSE The Florida Department of Transportation ent ered into a contract with the University of South Florida for the Center for Urban Transportation Research (CUTR) to determine t h e impact of Florida-based crashes on the National Highway Institute's (NHJ) expected value tables (Kansas City-based) and to develop, new, easy to use, expected value tables for Flor ida conditions. This document represents training "toolkit" for instructors of traffic conflict observers. This tool-kit includes important information on observer training, and should be reviewed along with the Final Report prepared by CUTR and t he Observer Manual on Traffic Conflict Techniques for Safet y and Operations (FHWA-IP-88-027, March 1990) before conducting conflict observer trai ning. The classroom training materials and the handouts provided in this report can be extracted at the i ns tructors discretion for observer training. INTRODUCTION According to FOOT Safety Engineers, the requirement for reporting traffic crashes (in state crash database) in Florida has reduced the number of crash reports available for engineering study by approximately half. (The state crash da ta base i n cl udes only t hos e crashes involvi ng hit and run, fatality, DUI, and inju ry. However, t he county crash databases include all reported crashes on all roads). This situation has resulted in an increasing difficulty i n the identification and justification of highway safety improveme nts. If the anticipated consequences of hazardous condit io ns are to be reso lved, there is a need to supplement the available crash data or sometimes use surrogate data (for examp le, conflict data and their relationship to actual crashes) to identify highway safety prob lems. The current National Highway Institute (NHJ) tables that list conflict data and their relationship to actual crashes are based on a study conducted during Summer 1982 in Kansas City, Missouri. Since then, mechanical characteristics and safety features of vehicles have u ndergone significant changes (e.g., anti-lock brak es ). Therefore, investigating the validity of the tables for current conditions and developing similar tables for Florida-based intersect ions were necessary. 1


The reliability of conflict data is dependent upon the ability of the observers to record conflict data accurately. Therefore, a carefully prepared obs.erver training program is essential to any use of the NHI tables (or the Florida based tables). Havi ng realized the importance of training observers to recognize and categorize t raf fic conflicts consistently, CUTR conducted an extensive observer trai n ing program (for comprehensive details refer to Development of Expected Value Conflict Tables for Florida Based Traffic Crashes, Final Report, April 1996) as part of the study. B ased on the train i ng program and subsequent traffic conflict observations (conducted by CUTR in the west central Florida i n summer 19941. this training tool-kit was developed. The training tool-kit is int ended to serve as a training aid for traffic safety engineers and supervisors at public and private transportation agencies, who plan to conduct traffi c conflict observations to estimate number and type of crashes and to make decisions and recommendations for highway safety improvements. The tool -kit contains classroom training materials and ha ndo uts distributed among trai nees, sixteen field slides, and a video tape These items are briefly discussed in the following sections. For further in form ation on field work requirement and scheduling and problems encountered in field and remedies used, refer to the Final Report. CLASSROOM MATERIALS AND HANDOUTS The classroom training materials include inst ructor's topics and short notes, schematic diagrams used to describe traffic conflicts, and photographs of actual traffic conflicts. The instructor's topics and short notes include t h e i ng a ge nda, topics, and items to be covered under each topic. The enclosed schematic diagrams and four photographs of conflicts a t two intersections were copied from the FHWA IP-88-027 (January 1989), and TRB-219 (February 1980). These materials can be effectively used to formulate a training program and to exp lain traffic conflicts at intersections. The handouts Include copies of appropriate pages of Traffic Conflict Techniques for Safety and Operations. Observers Manual, FHWA IP-88-027 (March 1990), a t ip l ist, observation sheet. and intersection sketch sheet. These handouts can be distributed 2


during the classroom training. The observation sheet lists the twelve types of conflicts and additional space is provided to record any reoccurring (or other) events. Location, type, and leg number of the intersection, observer's name and survey date and time are recorded in the sheet. The intersection sketch sheet provides space to draw a rough sketch of the intersection and to list physical characteristics of the intersection. The tip list includes tasks that the observer should perform before leaving for the survey and some helpful reminders for personal comfort during the observation period. Changing some items of the tip list depending on the locality of the survey site may be necessary SLIDES A total of sixteen slides is included in the training tool-kit. These slides were taken from the observers' view point of actual traffic conflicts. The first four ( 1) s l ides were taken at 4 leg signalized i ntersections in an urba ri environment All four slides show right-turn same direction conflicts (in the second slide, the second vehicle in the conflict is the yellow truck). The next three (5) slides were taken at a 3 leg signalized intersection in an urban setting. The first and the third slides show a right turn same direction conflict and where as the second shows a left-turn same direction conflict. Slides 8 and 9 were taken at a busy 4-leg signali z ed intersection in Hillsborough County. The first slide shows a left-tum same direction conflict and the second slide shows a slow vehicle same direction conflict. Sl i de 1 0 was taken at a 4-leg signalized urban intersection and shows a slow vehicle same direction conflict. The observer at this leg is seen in a white car before the bill board. Slide 11 was taken at a busy 4-leg unsignallzed urban intersec tion in Manatee County. It shows a slow vehicle same direction conflict. Slides 1 2 and 13 were made at a 4-leg unsignalized rural intersection. Slide 14 was taken at a 3-leg unsignali z ed rural intersection. The last two slides ( 1 5 and 16) were taken at 4-leg signalized intersection under a suburban setting. The two slides show slow vehicle same direction conflicts. 3


VIDEO TAPE The video tape documents CUTR's experience in conducting both observer training and conflict data collection in the field. The tape is intended for engineers and supervisors who would be responsible for observer training and conflict data collection. It is recommended that the tape be viewed prior to setting up an observer training program. The contents of the tape can be divided into two main parts: excerpts from the classroom training of observers, and techniques in fie ld data collection. The remainder of the tape includes the actual field observations made at two intersections in Hillsborough County. The first intersection is a 4-leg unsignalized rural intersection. Observations from all four legs were included with a brief description of the orientation of each l eg Second intersection is a 4-leg signalized urban inte rs ection. Observations from two legs of the intersection were inc l uded with a brief description of the intersection and the orientation of each leg. This part can be used during the classroom training to demonstrate observer positioning and observer's field of view perspective during the observation period. 4




TRAFFIC CONFLICT OBSERVER TRAINING AGENDA I. INTRODUCTION Project obfectives of project who would use the results and for what reasons? your involvement/contribution to the pro ject importance of accuracy and reliability Intersection information legs (approaches) through traffic flow direction (N bound, S bound, ... ) laneage traffic direction (same, opposite and cross) right of way (protected/permitted left turn) II. DEFINITION OF CONFLICT General definition A n event involv i ng two or more road users, In which the action o f one u ser causes the other user to make an evasive maneuver to avoid a collision Road users : motorists, pedestrians and cyclists. Conditions for a traffic conflict (in the study) Presence of two or more vehicles The vehicles must be on a collision course [i.e., the vehicles must be attempting to occupy the same space at the same time 1 How do we know whether it is a conflict? (detect any erratic maneuver) Primary requirement: action of lead vehicle (vehicle #1) places other vehicle (vehicle #2) on a collision path unless evasive action is taken by other vehic l e #2 to avoid a crash. 6


An evasive maneuver Is evidenced by brake-light indication front lounging of the vehicle or squealing of tires swerve Examples (The fourteen examples in Traffic Conflict Techniques for Safety and Operations Engineers Guide, page 26-29) Primary and secondary conflicts If two vehicles are involved in a conflict. it is a primary conflict. If a third vehicle is placed in danger of a collision due to the evasive maneuver of the second vehicle, it is a secondary conflict. The difference between the primary and secondary conflicts is that, the third vehicle is responding to the second vehicle that, itself is in a conflict situation. Physical boundary of conflict Within 1OOft upstream or downstream of immediate intersection area Ill. CONFLICT TYPES & EXAMPLES Conflict is classified from the second vehicle's (in the conflict) point of view Signalized intersections Same direction conflicts: left-turn slow vehicle lane change right-turn 7


Opposing directi on conflicts: leftturn right-turn on red Cross traffic conflicts: l eft-turn from left through, cross traffic from left right-turn cross traffi c from left left-turn, cross traffic from r ight through, cross traffic from right right-turn cross traffi c f rom right Unsignal ized intersections Same direction conflicts: left-turn slow vehic l e lane change right-turn Oppo sing d i rection conflicts: l eft-turn Cross traffic conflicts: left-turn from left through, cross traffic from l eft right-turn cross traffic from left lef t-turn, cross traffic from right through, c r oss traffic from right right -turn, cross traffic from right IV. INTERS ECTI ON CATEGORIES BEING SURVEYED Signa li zed vs. unsignaltzed 4-leg vs. 3leg laneage 8


V FAVORABLE CONDITIONS FOR CONFLICT OBSERVATIONS No rain, no fog No major traffic incident or construction/repair [that would affect the traffic flow] No stalled vehicles Good visibility Dry pavement Self judgement on conditions (e.g .. traffic congestion) at intersection May need to look l ittle beyond i ntersect ion boundaries VI ON THE OBSERVATION DAY a) Read the manual before t he survey day b} Take items in the tip list c) Be at the assigned site 30 minutes prior to t he survey d) Log sheet e) Familiarize with the streets and the traffi c movements before the survey f) Observation sheet g) Look little beyond in tersection boundaries h) Intersection sketch General information of intersection Check list of the sketch Adjacent land use on each quadrant Urban/rural [curb & gutter specifies u rban condition) % of out of county/state license plates [heavy/moderate/low, subjective determination] % of t ruc k traffic [heavy/moderate/low, subjective determination] Weather condition during observation period Traffic volume 9


. : ... : ; .. .. : >. . FiJ:Ure (A) A traffic conflict with an oncoming left-tum vehicle. . . ; .. : ... -.... .. Figure (B) A traffic conflict with a ci'OIIs-street vehicle. .. . :: ... . ..: . . .. :,,;. . : ...


Figure (C) A traffic conflict witb a crossing vebiele I '= .. ,. Figure (D) A traffic conflict witb an oncoming vehicle.


West North Approach 1 i N WestbolDld East South (ObseJ:Ver position) Approach Approach


I I I \. . Figure 1 I..eft-tum, same dill!ctio n conflict


I I gl = t\ Figure 2. Right-tum, same direction conflict


I I I t __ ----I Figure 3. Slow vehicle, same direction conOict i \ J 1 i I


I I I J ;:J G '=' I I Figure 4. Lme change, same directio n conflic t


I I l Figure 5. Opposing left-tum conflict l l l i I I I


I I ; I .... .A>. / -I I I Figure 6. Opposing right-tum o n red conflict


l l------' \ I I I I I '.:.------Figure 7. Right-tum, cross-trnffic from right conllid


. I I 6Y -. \ I Figure 8. Left -tum, cross-trnffic from right conflict


I ---------- C o:o I ------1_1 "\ Figure 9. Througb, cross-traffic from right conflict


I I . -I I Figure 10. Right-tum, cmss-tmffic from left conflict


1 I ,<5Y --.- -I" I I Figure 11. Left-tum, cross-tr.lffic from left conflict


I I I IC!Id I [JJ 1FI = I I Figure 12. Through, cross-tJ:affic from left conflict


I I t I -l I I Figure 13. Slow vehicle, same direction SECONDARY conflict


t ,L ljl ---------------I Figure 14. Ri.gbt-tmn, cross-trnffic from right SECONDARY conflict


I /J ___..,. R =-I p I I Figure 15. Left-tum, cross-traffic from left SECOJ\'DARY conflict


INJERSECTlON mAFFIC C.ONFLICTS 1 3 6 .. 5 County:----lntersectioo type (as in schedule): Ust #: Location: leg nwnber: _ Day: Date: Observers nrune: Length of recooiing period: ___ Lcllol\un Righlol\t m Opposing Right-cum Through Rigl\lrum Leftl\lm Throogll

>ate; :>rawn and prepared by: County: : Intersection at : Intersection type (as on the schedule): Pavement striping: Yes No ; Curb & Gutter: Yes No ; Percent (guess) of out of county or out of state license plates: heavy/moderate/low Percent (guess) of truck traffic: heavy/moderat dlow : Traffic volume (guess) ; heavy/moderntdlow Weather condition: 0 Reoccuring traffic events (con:flicts) 1


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TRAFFIC CONFLICT SU RVEY TIP LIST Before you l eave make sure that you have these items with you for the survey I Schedule of survey intersections 2 Map showing the location of the intersections 3 Authorization lett er (keep on your person) 4. Personal identification ( eg. driver' s license, student ID etc ) 5 Orange safety vest 6. Pencils and an eraser 7 Watch 8. Observation sheets 9 Copy of the Observer' s Manual for reference purposes I 0. Daily log sheet II. Intersection sketch sheets 12. Clip board or har d surface For your comfort, consider packing I drinking water 2. a bat 3. sunglasses, sunscreen 4. lunch, snack, cooler with soft drinks/juices etc. 5 folding chairs 6. money for drinks snacks or meals. Should y ou have any questions regarding the survey, please call CUTR at (813) 974-3120.


Traffic Conflict Techniques for Safety and Operations--Observers Manual Publ icat ion No FHWAIP-88 ... -. U.S. Deponmem of Transportat ion Federal Highway Administration January 1989 : Research, Deve l opment and Technology Turner-Fairbank Highw ay Research Center 6300 Georgetown Pike McLean Virgini a 22101


FOREWORD This provides beslc background inform ation fer persons no are ass igned to obse rve traffic conflicts in the fie ld The manual con tains defini:ions o f ;:r affic conflicts 1hich typically o cc ur a t in;:ersections .tell es s:ep -by-st: p fo-co n ductinQ the s u r v : y Experifnceo o bs e rv ers and e n 9 ineers 11 fin d t h e m anual t o :-e a han d y refer e n ce so u r ce and in trainin g new per sonnel. P ersons w h o hav e not pre vio usly con d ucte d a traff ic c o nflict s urv e y s h o u ld rea d t h i s m a n ua l care f u l l y a s a f irst step i n l e ar n ing to acc urately o b se rve a n d record t raffi c conflicts. ori-= .. St anle y R Office of implementat ion :nis 1s tii sseminate o unCer tne sponsorsn1p cf the D e partment iransportatlon i n the interest o f information excha n g e The States Governmen t assumes no iiabi iity fo r Its con ten t s or use t h ere o f T h e contents of t hi s repor t reflect the v i e 1s o f contractor who i s resp o n s i b l e for th e f a c t s and t h e accur acy o f t h e data presen t e o h e r ein The o: not r.e cessa:"llv ofiic";! "J'!" po;:y ... :"1: J.;oartme:"'t. io;;: . . :-: : ... 1:. ....... 4 .... c.. --........ ..


No. i l I FOR - t D -1 oeutnentati on t"'o;c i ' : 6 l Ianna[\' 198Q F '" i#rm.in9 O roo-' t!lltOI\ TR!IF F!C CONfliCT TECHNIQUES SAF E T Y AND OPERATIONS Observers a 1 Oll;o,.iteli Ot'l R ,,:u:"' ..,;t i Parker, Jr. a n d C.V. Zegeer 9, P,r1ormi t'l9 Or<;o-.,inltion ond Acl.trclf. Hart in R. Parker and Associates, Inc. 38549 Laurenwood D r ive l O, Work U11o 1 No. f T RJ..I$) N C1' 3A9C0093 l I. C;>nhotl o G ront Nq, ;:ayne, 1-lichigan 48184-1 073 )-;-:;--;::-:-:--.-:-;--:--:;--=-:-"T:-:;:;::-:-:------------------ll3. T yr .. c ... Period 12. .t..? tM)' Nome ond Manu a 1 Offi c e of Imple mentation (HRT-2 0 ) f ederc 1 nighway Administration 630 0 Geor g eto1m Pike, T k lean. 'liro i ni a 2 210 1 Nan ager: October 1 986 J u n e 1988 ; nanual orovid g s oas i c backcroLi n o an G s t e pby-ste : for traffic at 'Ths manuc.) l!as pr-ep a r ed : : 6. aid sourc: f::rr persons .: h o t h e iitv c : i 0 W ..,,; _,..., = ...... u .. __ 1 ....... ..,: ... -:.. ....... oreviou s : .. c.n;:: :.1: :;;.:r .:s; ihis m anua l a .... .:.:-.... ,, . :::.: """G --.... .=::: . .. < . ...................... :.':' --... .... prob lem s a n d t o e ffec t ; J=ness -Jf training techn iques, as "ell as proceoures fc-:-ana l yz i n g an d inte r the results o f co n flic t s u r veys: z r g p r esented i n the engi n e e r:! (FHWAI P -88-026 ) ions, i'-1 anua i cbserva-=; 1 ons. *' : .;t'=:;n: _,:::.:. -: !too& t ceor.: Jr:.s. :::is : o c u men:: is cvailabie Nationc.; .... ... "... ; .,. .... .... -:.-;:; ... :'"'--. "' .... ,.. -. "' .


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TABL E OF CONTENTS Sec t ion P ape CHAPTE R 1 I NTROOUCTI ON. . . . . . . . . . . . . . . . . . . . . . . . . 1 Bac kgrou n d . ..................... . ......................... ..... . l Traffic Conflict S urvey.............. ............. ........ . . . . 4 CHAPTER 2TRAFFIC CONFLICT DEFINITIONS............................ ... 4 General D efinitio n .............. ........... ..... ....... ... . ..... 4 Ope ration a 1 O e f in i t i ons .................. ....... : . . . . . . . . . 5 Other Types o f Traf f i c Eve nts .... ......................... . .... 15 CHAPTER 3 -RECOGNIZING TRAFFIC CONFLICTS ............................. .. Exam p les .......... . ....... . ................. . . ........ .... -. Unu s ua 1 i ntersection Geomet r i cs ................... .. ........ ...... CHAPTER 4STARTING THE TRAFFIC CONFLICT SURVEY ..... ........ ....... ... 2 0 Preparin g f o r t he S u rve y ......... .............. ......... ... ... .... 20 A r r i ving a t t he Study L oca t i o n ... .... ... .... .................... . ? CHAPTER 5 -CONDUCTING THE SURVEY ...................... .............. .. Time Schedu' l i n g .... .......... ................. ... ... . ........ . . . h t ..;sing t e Locn bOaro .... ............................ ....... . . . c t 1 a n i 1 1:::. :-Oriit .......... .............. ... ... . . .... .... : v i iecting Otiler Uata .... ......................... . ......... . . S peci a l Pro blem s ............. ... ......... ... .................... 35 Safety Consi d e rati o n s . .......................................... 35 Completing t h e Survey ............................................. REFERENCES .. o o o i i i


F io ure 1 2 3 4 5 6 7 8 9 1 0 11 12 13 1 1 5 16 l 7 10 -20 22 -;";t ---Z l A

TRAFFIC CONFLICT TECHNIQUES FOR SAFETY ANO OPERATIONS OBSERVER'S MANUAL CHAPTER 1 INTRODUCTION A traffic conflict is a traffic event involving t h e interactio n of two or more road users, usually motor vehicles, where one or both drivers take evasive actio n such as braking or swerving to avoid a collision. A t r a ffic conflict survey is a systematic method of observing a nd recording traffic conflicts and other events associated with safety and operations A person who conduc t s the field survey is known as a traffic conflict observer. This man ual provides basic background i n formation and standard procedures for traffic conflict observers. The manual contains definit i ons of traffic conflicts whic h typically occu r a t intersections as w ell as s tep-by-step instructi ons for co nducting t h e s urvey. E xperienced observers a nd eng ineers 1ill f i n d t h e manual to be a handy referen ce so urce and a n aid in training nel't personne 1. Persons l'tho h ave not conducted a traffic confli c t survey s h o u l d caref u lly tead this manual as c. first step in lear ning how to o bserve and record confiicts. Secause the results of a traffic conflict survey are use d to m a k e i mpor tan t decision s co ncerning traffi c safety and operations, i t i s imperat ive that conflict s be recorded I n a uniform or standard manner. Observers must participate in a formal traini n g program to help them r ecognize confl icts u nder a variety of traf fic and condi t ions. O n e should not be expected to count con f lict s based o n reading this manual alone The training program conducted by the engineer, i s essenti11l to assure uniform and accurate data col iection. Training procedures, as well as met hods for a nalyzing and interpreting con f lict data are ciescri be d i n the eng i nee r s g uide. t>l The s u rvey tech ni q ues described i n this manual previae a cost-effect ive m e t hod for accuratel y measuri ng c confl icts s ignall zed an.: unsignalized intersection s The definition s a n d procedures are ba sed o n the results ?f years o f extensive research, experimentaticn: and !r: future : t is anticipated t hat stan<.iardized procedures 11 d:veiopec; f':':" other r oadway situatio n s suc h as freeway entrances a n d ex its, ng areas, 1 n idblock locati o ns, and constructio n zones Background For m an y years traff i c accidents have been used as a d irect meas ure o f safet y I f an u n u sually high n u mber of accide no:s occur at a location, i t is probab l e t ha t someth in g associated with the design or traffic operation i s unsafe. Traffic e ngineers, therefore, use acci dent data to determine: locations are most hazardo us. What ki nds of hazards are present. Whether a change i n the design or operation ha s be e n effective.


Sut, there are many prob l ems w ith accident data. Ali accidents e r e not reported. D ue to manpo,er and budget 1 i mi tat ions in recent years, there i s g rowing trend na t ionwide by police agencies not to report propert y damage on l y accidents. For eo examples,.but t h ey s h o w that traffic conflicts a r e situations where a d r iver b r a kes or to a void a collision. i n 1 979 a dditionai extensive f i eld testin g was conducted to dev e l op standard definiti ons and refine t he data collection orocedure t o e nsure ':rained ob s e rvers cou ld orovide accurate The definition s and ;Jr ocedu r e s i n th i s man ual were t ake n from that research study ;.nothe r major stucy, c omple t ed in 1985, provide d proof t hat some t raffic conf1 icts and accidents at intersections were related.[SJ In fact: t he ;ound traffic conflicts are good surrogates f o r accidents. M eans c onfi i : : data may be used a s a substitute for


. : .. > .. . .... t : j ...... , .. .. ..\ confiict '-'lith an onco:ning lefttu:-n vehici"!. !.


Traffic Conflict Survey A traffic con flic t study is usually conducted under the directi on of_ traffic engineer who determines that the stud y i s needed, schedules t he activities, supervises data collection, and performs or supervises analysis. The engineer a lso interprets the findings a n d makes decision s a n d recommendat ions concerning intersection i mprovemen t s Field data co 11 ect ion is norma lly the function of traffi c technicians, and/or planning personnel. An e ngineer's guide is avai lable for the engineer who till make the decisions about where and when to conduct a conflict study, and how to analyze a n d interpret the results.[l] A traffic conflict survey usually takes from several hours to several days of careful manual observation of traff i c at an intersection. Specific procedures are used to assure uniform data collection so that valid comparisons and judgments can be made. A survey requires one or mor e observ ers who follo a set sche dule a nd perform a number of separate but related t as k s These t ask s i n c l u de recordi ng dimensions an d other details abo u t the in t e r s:ction s"ch as the t ype of traffic co ntrol dev ices in p lace. The i ; e:isc required t o make judgments abou t the traffic problems and causes, ano mos t importantly, to observe and record traffi c events. l!D s o phl equip ment i s t o m ake a conflict survey !:1 the past s c rr:e a g e n c ies h c v e used m o tion picture c.r video e q u ipmen t to r ecord ho t,ever: ::.o improve accuracy and reduce C ata coi iectlon costs: obser'lati ons Gf conflicts in t h e field are recommend e d .,:.?\opt: r 2 o f t h i s m anuc.i provides detai ied of the types o"f t r affic conflicts that are observed and recorded conflict survey. ::1 cha pter:>, examp les of several t raffic situations a r e given a l ong 'tJith interoretat ion o f how these events should be handle

general definition, however, does r ule out actions that nearl y all d rivers t ake u nder t h e same conditions such as norma l stoppin g for a STOP sign or red traffic signal. Conflicts are vehicle interactions whic h can lead to accidents. For a conflict t o occur, the road users must be on a co llision course; i .e., the users must be attempting to occupy the same space at the sam e time. The p r imary requirement of a traffic conflict is that the action of the first use r p laces the other user on a collision path unless evasi ve action is taken by the othe r user to avoid the accident. Sometimes the othe r user i s either unaware of t he collision potential or has poor judgment i n estimating time intervals and clearances and does not make an evasive maneuver. Collisions and near m iss situations t hat occur without evasive maneuvers, or when t he evasive action is i n a dequate or inappropriate fol" cond itions, are a lso record ed as con flicts unde r the general definition An intersection traffic conflict i s described as an e v ent i nvolv ing t h e f oilotling s t ages. Stage 1 T h e first vehicle makes a maneuver; e.g., pul ling out from the cross street Stage 2. A s econd vehicle is p l aced i n dang e r of a call is i on. Stage 3. The driver of the sec o n d vehi cle reacts by braking or serv i ng. Stage 4 The second ve hicle then continue s to p roceed throu9h t h e intersection area. The 1 as t s t age is necessary t o con v i nee the observe r that the second ve h i c 1 2 was actu ally responding to t h e manrcve r o f the fir s t ve hicle a n d not, for example, to a traffic control dev i c e or nearby drivevtay or m e dian o pe ni n g. The evasive maneu ver taken by the. secon d vehicie i s evidenced by obvious braki n g or svterving. Braking is us ually observed as brake-ligh t indicati o n s howev e r some vehicles are Or-iv en \'li th inoperative braxe i l ghts. A r.Jticeabi::.:1 /ing of the vehicle or squealing cf t i r es in 1:he a b se n ce of b ra k e 1ig hts :s acceptab i e evi de nee o f a n i ve .... Operational Defini tions With in this general framework, a basic set o f c onflict d e finiti o n s 1ere devel o pe d fo r intersections, corr espondin g to the differen t typ es of man euve r s and relat ed acc ident patterns. Similar to the manner i n which acci de nts are grouped by type of collision, traffic conflicts are c ategorized by t ype o f maneuver. The primary types of intersection co n f l icts are: a Same d irectio n a Opposing left turn. Cross traffic. Right -turn-on-red. Pedestr ian. Secondary. -


Overall, 14 basi c intersection conflict situation s are useful in pinpointing safety and operational problems, and several other even t s may be important in special situations. The conflict definitions are presented in the fo i ng paragraphs a 1 ong with f igures i 1 1 ustrat i ng the event. T o vie,, co nfl lets, an observer is stationed on one intersection approach for a specified time period. A l l confl lets observed from that vantage point are recorded. Conflicts that occur on the other approaches are recorded by other persons or during different time periods when one observer is used The conflict defin i tion s were developed to give the observer a clear view of the evasive action; i.e., braking or swerving, taken by t he second road user. While the observer can see t he action taken by the first road user, the primary focus is on the reaction of the driver in the second vehicle. To aid in learning t he various conflict patterns, the position of the observer is marked o n each of the follo11ing conflict diagrams. Same-Direction Conflicts P. same-diecti o n conflict occurs ,th e n the first ve hicl e slov:s an d/or changes direction a n d places the following vehicle i n danger o f < rear-end collision. The second vehicl e brakes or swerves to avoid the co lfision, t h en contin ues t o proceed throug h the intersection area. The four basic types o f sam e -direct ion co nfl lets are describe d below. it should be not ed, h011ever, that all secondary conflicts (described later in a separate categoryj are also samedirection conflicts. Left-turn, Same-Direction Conflict A left-turn, same-di r ec t ion con flict occurs w hen t h e f irst veh icle sio"s make a l e f t turn, thu s placing a second, vehicl e i n danger or e a r e nd co 11 is ion ( see f i g ure 3). Same-Direction Conflict A ri c h t tu rn, same-d irection conf i i c t occurs \ then the first ver. c i e s: .J;IS t o make a r i g h t turn, thus placing a seco n d following 'ehicie in oanoe r o7 t rthile a p proach ing or passing thr o ugh the intersect io n, p l acing a second, f ollow in g vehicle in dangel' of a rear-end collision ( s ee figure 5). The reason the driver of the first vehicle s lows may not b e evident, bu t it could simply be a precautionary action, or a result of congestion or some o t h e r cause beyo n d the intersection. l

I I I I I I ---1-I I I I I x (Observer) Figu r e 3 left-turn, same-direction conflict. I I --' ll'---1--P-1'---l 'r-.1--. [ I I i I X (Observer) F igure o. Slow-vehicle, same-direction conflict. I I I l I I I I I X (Observer) F igure 4 Right -turn same-direction conflict. I I I I I . :.----.(j -.,_ I ! ( 1 I i I I :t (Obsarver Figure Lane-cha09e conflict.


vehicle in the new lane I n danger of a rear-end or s ideswipe collision. However If the lane chan ge is made by a veh icle because it i s in danger, itself, of a rear-end co llision with a no t he r vehicle, the following vehicle i n the next l ane is said to be faced not with a lane-change conflict situation but with a secondary confl ict situation. ( Secondary co nflicts are described i n a subsequent category. ) Opposing Left-Turn Conflict An opposing left-turn conf lict occurs w h e n a n oncoming vehicle m akes a left turn, thus p lacing a secon d vehicle, going in the other direction, I n danger of a head -on or broadside collision (see figure 7). In this and in the following conflict situations, the seco n d vehicle i s p resumed to have the right-of-way, and this right-of -way is threatened by the first road user. Situation s such as a second vehicle p l aced i n danger o f a collision becaus e t he drive r of the seco n d vehi c l e is run n in g a red lig ht, for example are not treated as traffic conflicts. These situations are describe d in the section on other t ype s o f traff i c even ts. I X (Observer; Figure 7 Opposing ieft-turn .


Cross-Traffic Conflicts A cross traffic conflict occurs when a vehicle o n the cross street turns or crosses into the path of a second vehicle on the main street who has the right-of-way and places the second vehicle in danger of a rear-end, sideswipe, or broadside collision. The second vehicle b r ake s or swerves to avoid the collision, then proceeds thro ugh the intersection area. Cross-traffic confl lets can occur from vehic l e maneuvers on the righthand and/or left-hand cross street approach Cross-Traffic Conflicts From the Right Cross Street Approach Right-Turn, Cross-Traffic-From-Right Conflict A righttu rn, cross -trafficfrom-right conf 1 ict occurs a vehicle on the right-hand cross street makes a righ t turn, thus placin g a seco n d vehicle on the main street i n jeopard y of a broadside or rear-end collision. See figure 8 for the directions of the two vehicles At si. gnal ized intersection s rig ht t urns on red ar e permitted, i t is sometimes desirable to fur ther subdivide the right turn category to identify conflicts related to right-turn-on-red (RTOR) maneuver s Left-Turn, Cross-TrafficF rom-Right Conflict A left-t urn, cross-traffic-from-right conflict occurs when a vehicle on the righ t-hand c r oss street makes a left t u rn, thus p lacin g a second vehic l e on the main stceet i n dange r of a broadside collision (see figure I I I f \ I I : i I i 1 l I x,>_ --1 r I t I l ;{ (Observe!') cigure a. Right-tum, cross-traffic from-right conflict. --J t '{ l ... J Figure 9. Left-turn, cross-trafficfrom-right conflict.


Through, Cross Traffic-From-Right Conflict A through, cross-traffic-from-right conflict occurs when a ve hicle on the right-hand cross s treet crosses in front of a second veh i c l e on the mai n street, placing it i n danger of a broadside collision (see f i gur e 10). Cross-Traffic Conflicts From the Left Cross Street Approach Right-Turn, Cross-Traffic From-Left Conflict A right-turn, cross-traffic-from-left conflict o ccurs when a v ehicle o n t he left-ha nd cross street makes a right turn across the center of t h e mai n street r oadway and into an opposing lane, t hus placing a v e hicle i n that lane i n da nger of a head-on collision (see figure 1 1 ) T his c o nflict is som etimes observed when the c ross street is na r r ow, or when large t rucks or buses make >fide right turns. Note that t h e f irst vehicle must cross the ce n ter l in e f o r there to be a conflict. Left-Turn, Cross-Traffic From-Left Conflict A left-turn, cross-traffic -from-left conf l ict occurs whe n a vehic l e o n the left-h a n d cross s treet makes a left turn, t h us placi n g a s e cond vehicle o n the mai n s treet in dan g e r of a broadsid e or rear-end collision (see figure 1 2 ) Through, Cross Traffic From-Left Conflict A t h r o u g h, cross-traf f ic-from-left co n f lict occurs w h e n a vehicl e o n the i s f t hand cro s s street crosses i n fron t of a secon d vehicle on 1nain p a c in it i n dan of a b r oa dside collision (see f i gur e ----------- -----------X {Observer } iO. ihrough, cross-traffic-from-rig ht confiic;.


I I I I I l --I hll I I I I;; (Obser ver ) i I l I I I 4 ____ oJ I I I I I X (Ob server ) Figure 11. Right-turn, cross-trafficFigure 12. LeT- urn cross-traffic-from-left conflict. f r om-left c onflict. . I i x (Obse rver) F igure 13. Through, cross-traffic-from-left conflict.


Right-Turn-On-Red Conflicts Right-tu rn-o n-red conflicts occur w h e n a RTOR v e h icle makes a turn and crosses into the lane of a second vehicle whic h h as r i g ht-of-way. The driver of the second vehicle brakes or swerves to avoid a broadside, sideswipe, or rear-end colli sion, the n pr oceeds through the intersection area. Opposing Right-Turn-On-Red Conflict An opposing right-turn-on-red conflict can only occu r at a signal ized intersection with a protected left-turn phase. I t happens when an oncoming vehicle makes a right-turn-on-red during the protec t e d left-turn phase, thus placing a left turning, second vehicle (which has the r ight-of -way) in dan ger of a broads ide or rear-end collision (see figure 14). Right-Turn-On-Red-Froiii-Right Conflict A right-turn-on-red-from-right confl i c t i s a s pecial category of the right-turn, cross-traffic-f ro m-r ight conf lict ( see figure 8). The r igh t t ur n on-re d conflict occurs only at s i gnal ized intersections when a RTOR vehicle on the r ig h t -hand cross street makes a RTOR maneuver and p l aces a second vehicl e on the main street in dange r of a sides1ipe, broadside, or r ear-end colJision. I I I I I I I I x (Observe r ) Figure 14. Opposing right-turn-on-red conflict. 12


Pedestrian Conflicts There can also be pedestrian conflicts. They occur when a pedestrian (the road user caus ing the conflict) crosses in front of a vehicle that has the rightof-way, thus creating a possible collision situation. T h e vehicle brakes or swerves, t hen continues through the intersection area. Any such crossing on the n ear side or far side of t h e intersection ( see figures 15 a n d 16) is liable to be a conf l ict situation. However, the pedestr ian movements on t h e r i ght a n d l eft s ide s of the intersection are g enera l l y not con sidere d to create conflict situ ations if the movements h ave the righ t-of-w ay, such as duri n g a WALK phase. l n some cases, the observe r may b e asked t o count b icycle confl icts. These conf licts are s i m ilar to the pedestri a n conflicts described above e xce p t the road user ca u s ing the conf licf i s a b icyc l ist. I I I I I I I I l I* I I I --_ --' ( i i I I I l i I 11 I I i I lx I ' I I (Observe r ) I x (Observer; Figure 15. Pedestria n, far-side F igure 16. Pedestrian, near-side conflict conflict. 13


S2condary Conflic t s I n a l l of the foregoing conflict situations, when the second vehicle makes an evas ive maneuver, it may place another road user ( a third vehicle) in danger of a col lision. Thi s type of eve n t is called a seco n dary conflict. Nearly always, the s ec ondary co nflict will look much like a s l ow-ve hicle, same-direction conflict or a lane c h ange conflict. The d i f f ere n ce is t hat, in a secondary conflict, the third vehicle is responding to a second vehicl e that, itself, i s i n a con f l ict situation. Some examples are shown i n figures 17 and 18. By definition, only one secondary conf lict for any initial conflict should be counted Even if a whol e line of cars stops because the first vehicle turns left, the event would be recorded as one left-turn, samedirection conflict and one secon d a r y conf l ict. \ I I I I I I ; \ l l l ,-l figure 17. R ; ,..... IQI . h ; :'Gt>sory::.r., f \ ... ... / Slow-vehicle, same-direction secondary conflict. 1 4 ! I I I J I l 1 ----{Ql P. i l I I ; I I I 1 : fCOs=-rv::."" . \ .... : Figure 18. Right-turn, crosstraffi c from-right secondary c onflict.


Other Types of Traffic Events for some studies, the engineer may request the observer to count other types of traffic events, which are not define d in t hi s manual. For examp l e, to examine the effectiveness of a new traffi c signal disp lay the obse r ver may be aske d to collect th e number of red-light violations ( a driver who c ro ss e s the stop line after the light has turned red), and the number o f red-light violations that resulted i n a con flict with other road users. Note t hat neither a red-light violation nor the resulting violat ion co n flict is a traffic conflict under the conditions outlined in the general defin i tion. In any case, the two ev ents may be appro p riate measures for some studies. In these special situations, the enginee r will define t h e events to be counted and p rov ide observe r train ing prior t o data collect ion. O b servers shoul d always rec or d any unusual or u nexpecte d events dur ing a conflict survey. Even if the event is rare or n ot descr ibed i n this manual or during t raining, it may have important implicati ons con cerning safety and operati ons a t the intersection. These events s houl d be recorded i n the comments sec t io n o n the conflict data form. CHAPTER 3 RECOGNIZING TRAFFIC CONFLICTS A traffic conflict s urvey requires the observe r to r eco gnize s p ec ific conf l ict t ypes fro m a > lid e varie t y o f traffic events. It i s not possi b l e to describe in th i s manua l every possible traffic event and classify it int o one of the conflict ca t e gories. T h e o b serve r wi 11 have t o j udge mos t situation s using experience, and by applying the principles prese nted earlier. To aid in recogni zing and classifying conflicts, the fo llowing examples of traffi c s ituations are offered. StudyinQ th e se 1 ec ted ex amp 1 es ,i 11 he 1 p i n makin g t h ese judgments. Examples In ail of these assums the conf!ict o:: t::e sc:.1: : as s hown i n ficu r e 19, tie'l!lno northb o unC :s ..-::-.:: ... -As. J ot. ... \.1, :cc:.l...u;...:;:.::;!"n ....... ... aescr ibeo and then interp reted 1. The s ignal t u rns red for n o rthbound traffic, but a driver apparently does not notice it until the last minute, then slams on the brakes. The i nterpretat ion depends on the other traffic. as would normally be the case, the intersection is empty when braking b egins, t here is n o conf lict. The d r ive r is just respondina t o the s i gnal. But i f a westboun d v e hic ie is ie the intersecti o n classify the e v ent as a throug h, T hi s would prob ably be r are, a n d the obs erver sho<:1c :naK: :. note about i t on the c onf l ict dat a form. 2 A car on the right (east) approac h stops, starts to pul l out t o make a rian't turn then stops abruptly because the d r iver s ee s a 'lehicie that' just pas sed the observer pas .ition. ""'is s ":m ::-,o; ) .... .... ... ... oose:vern 1 y a nc;: . oou:1c 1 : : ..... : .. .,. . .... _.: ...... ::


West !h)rtn .C.pproach A,pproach (as Sou lh Approacll 1 X (Observer position) Figure 19. Intersection layout for the example traffic situations. coll i s ion I s there a conflict. If, however, the northbound veh icle else b raked o r S\"erved and the car from the right h ad pulled far e n ough f o n"ard to be in h i s path t hen a right-turn, c ross-traffic-fNm-rig h t con f i ict woulG be recorded. 3 A northbound car slows and turns right. Another car, right behind n, brakes severely and then it, too, turns right. t his cou l d b: event should be considered to t a c r lght turn ccn f t ict. : 7 the second tehiclc, however! tur n s intv c. drive w a y or mcKeE: 1 : f": shouid ne t rec orded a co n f i ic: because c;.:. kr:o ... ::.1e brakeo of the :=ir-'!t Oi :;;;: e .en 'cl ..... '""'oc::.or e t nrouf"'" t.u---,_ 1 -=!-! __ uJ =""'''-.... __ _, .... ;':". s::ecG c .:"turn i n;; ;ecorc t.:-: e e v !:nt c.s :. c:;r:f : : : ... ,.{, : .;. the signal is green for north and southbound t,.-affjc, northbound driver begins a left turn, then stops abruptly to avoid southbound vehicle which he did not see until the last minute. This is not a conflict This common situation often leads to acc;dents, hoever. Especially on four-lane roads, the oncoming southbound center-lane vehicles :nay be stopped .;aitin g t o turn left, hiding southbo u n d thr o u g h-vehicles in outside l ane But unless there is a leftt urn phase1 :1ave t h e "ight-of-way. ;:< the left-turn 'Jehi:l e does not h ave the right-of . i t not c l.essified as a conflict. HO\ofever, 1 7 :>bserveo cft;n a n intersecti on, make a note on the f c r:n. 7 >;n e observer was or. the nort h approacn and cr-iver :Jouid be as a n cp oosing ....... -_ ..


5. During the green cycle on a four-lane street, an oncoming southbound vehicle makes a left turn, causing drivers in both northbound lanes to brake. A l though this could be debat!!!d it appears most logical to count this as two opposing left-turn conflicts. Although t here is only o ne instigating vehicle, an acciden t cou l d have occurred with either northbound vehicle i f t he drivers had no t reacted. Also, this is not a secondary conflict situation, because the two northbound vehicles reacted independently t o the lef t turner, not to each other. 6. A car is stopped with a flat tire on the north side of the intersection, blocking the right northbound lane for half an hour. Meanwhile, northbound traffic is slowed considerably because it is forced to maneuver around the disabled vehicle. Frequent slow-vehicle and secondary conflicts are noted. The conflicts sho u 1 d be recorded unless traffic b a c k s up (stop and go con d ition) through t h e intersection. M a k e prom inent notes about t h e situat i o n and if possible, exp lain i t personally to the engineer. He may decide no t to use the data, but it is better to record t he data, even if t hey vii 11 no t be used, th an to miss important insights about the traffic operatIons. 7 Same situation as noted in example 6, except traffic flow fs reduced to stop and go conditions during the green phase, and nearly every northbound vehicle brakes one or more times approaching or going through the intersection. The Traffic Conflict Technique does not appear suitable during periods of congesti on. However the existence of traffic congesti o n is possibly i ndicati ve of operational deficiencies. During such times, cease m a king formal co n f lict coun ts, but carefull y not e any causes for the congestion (it be s i m ply heavy traffic) and long i t lasts. S. Every 10 minutes or so, a city bus slows and stops just north of the intersection to discharge passengers. Cars behind the bus are forced to brake swerve. Record t hese events a s s low-vehicle conflicts. a u t i t i s e x tremel y impor tant to note the cause. T his may o r may not oe judged a hazardous situation--that is for the traffic engineer to decide--but make sure tc record the 9. 1ne observer hears t:ne squeal ot g_rakes behinci (south of) his posiTurning, he sees a heay, slow-moving truck and, behind it, the that had just braked. This i s not a conflict. The observer is COllnting o nly t he events between him and the intersection. The p u rpose of t he stod y is to learn more a b out the i ntersecti o n Chances are t h a t events be h ind the o bserver {such as the slo,T-movi ng truck) have little to do with t he intersection itself. Sut, i f the observer bel i eves t h e braking was d ue to the i ntersection (for example, the truck ,.as moving sloN i y because the signa l was going to cha n ge), a s p ec i al note should be made on the data form. 10. There is a fast-food restaurant 200 feet north of the intersection, and many vehicles slow to turn right and enter the driveway. Often, other northbound vehicles are forced to slow during, or after, the time they cross the intersection. These incidents s hould b e recorded as s 1 on-ve h icle con f 1 icts if t he brakina vehicle i s on t h e o bserver sid e of or in the :ion. : ; the vehi c i e is nortn of the intersection, th i s i s not a n intersec:icn C3nf1iCt and sho u ld not. Je recorded. i 7


happen s fre quently mak e notes abou t i t A l t hough t here may n o t be an in ter section pro blem, the o bserver may hav e located a driveway pro bl e m t h a t bears on how the i ntersection operates. 1 1. A car, parked at a meter ahead of the observer, pulls in front of another vehicle, causing it to brake. This is a con f l ict; the question is, wha t k ind? Arg uments coul d b e made for cal l i n g it a slow vehicle conf lict, a l a n e chang e conflict, or e ven a r ight-turn, cross-ttaffic-fro m-r ig h t conflict. If this does not ha p pen very often, the c lassificati o n probably does not mattet v e r y m uch. I t is preferred practice t o recor d it a s a s l ow-v eh i c l e conflict then to note the cau s e 1 2. A southbound cab enters the intersection, then makes aU-turn and heads north. The driver of a northbound veh icle applies brakes to avoid a collision with the cab. If thi s ha ppe ns very often, make up a s eparate column, d efine t h ese as U-tu r n conflicts, and c ount them. Qtnerlfi!C ,cvo d 1" whiele &eAPliet; art::! ,.ete the eassa 13. A southbound vehicle makes a left turn at the intersection crossing in the path of a through northbound vehicle. The observer hears t he tires squeal an can see the f r o nt of the northboun d vehicle dip f orward indjcating sudden deceleration, but there are no brake light indications and the northbound driver did not attemp t to swerve to avoid the impending collision. Thi s is definitely an o pposing l eft-turn co nflict A s m all percent age o f vehicle s have brake lights t hat are inoperative. To r eco r d a c o nflict, h owever, ther e must b e some visual and / o r audible evide n ce s uc h a s the sq u e a l i n g o f tire s t o conv i n c e the observer that t he d river was attempt i n g ev asive action. 1 4 The signal turns red for northbound traffic causing a northbound 'lehicle to slow, then come to a full stop. At the last second a fol low i ng northbound drive r slams on the brakes, the vehicle skids, and finally comes to stoo just before reaching the lead vehicle stopped on t he aporoach. S: '3eflnition, thi s i s not a conflict because t h e lead vehicle stopped i ega11y a red sion al. F o r c same-direction c on flict t o occu';"'. t h e s i onci :1i.JSt Oe 1:2r:13; However. as a c cidents reiated t o this maneuv e r at i nterse-.:t ions, rhe o bserver shouid note the e vent on the c onfl i c t form. )';"'a king o r s werving b y a foi l owing v e h icle may i ndicate signel !".elated ;>roblem especially if eve:1t i s repeate d a numbe t c 7 :imes

record these swerves as rear-end conf l ict situati ons. shou l d be alert for lane-change conflicts, whi ch are i ntersections. H owever, otherwi se t h e observe r rar e at most


CHAPTER 4 -STARTING THE TRAFFIC CONFLICT SURVEY A traffi c conflict survey includes maki n g c onflict counts a l ong with collectin g other data needed to a complete stu dy of t h e location The co l lected d a t a can b e use d to answer question s a bout safety and operational prob lems; to recommend correcti ve treatments; or to show the effecti veness of improveme nts already impl emented, as in a before-and-after study. T he traffic conflict s urvey can also be a portion of a larger study w i t hin a safet y upgradin g program. In this case, traffi c conflict data are used alon g with traffic accident data, sign a l warrants, capacity analysis, and other engi neerin g data needed to identify prob lems a n d recommend improvements. Preparing for the Survey B e fore leaving for the stud y location assemble instructions, equipment, and mate r i a l s n eede d for the surv e y. c Observati on procedu res as discussed :i t h the engineer. a Schedule of survey lo cations o 11ap s h owing location o f study sites. o S u pe rvisor's telephone n u m ber. o Persona l ide ntificatio n ca rd a l!lser9. e Tablet. o Pen cils. o flatch. o S t op watch t h e engineer's Thes e i n c Ju d e : o .Camera f i l m (at leas t 20 e x posures for a four-leg i ntersect i o n ) o Folding c hair (op t ional ) > Water. o Data c o l lection f orms Safety vests. Copy o f t he Observer' s Man u a l f o r referenc e purposes. T h e observation procedure s inclu d e the number o 7 n ee d e d; legs t o b e studied, s p ec i a l c onflict types, i f a n y a n d ot'ner data to o e collected ; and hours of observation n e eded. This in f o rmation wiil be o,-c : i ded by the engineer. These proce d u r e s are descr i be d i n the en f)i nee;; s [11 T h e schedule of s urvey location s should list f u t u r e study sites; h;cr. cou l d a 1 so b e used i n emergency s ituation s t hat is, i f fo r some reason data cannot be collected at the scheduled site. I f t h e observe r is not fam i liar .

Soare vanc11 s one e for additional notes are a necesslty. A \\'atch neeaeci :c note count start times, anct a stop .,,atch i s needed to accuratel y jetermine signal timing. To adequately record t h e physical features of the stuciy location, about f ive photographs per approac h are needed !\ fol d in g chair should be included as part of the observer's equipment i n : ase he i s unable to use his car or i f the temperature makes observations from car uncomfor tab l e. Ori nkir.g water is highly desirable, especially on hot scfety vest o:" other eq u ipment l"equired b y th e age ncy should .:; , o--"" "' : r + ;..,, .:, o ., ec i n a o"her n e a r e .. r ::_. $:::.; =. ":'" -. > 1 hll .., l .: ... v .... w .... 1,. ...... "' "'"" .... .... .. :Jnsiderations are disc:1ssed 1 e.ter in this manuai. t.. cr co1ied:.i o n forms: including "!re as f ::i .iO\>IS: Physicai Inventory, t: ,_>' : .. ks, an" Jn t<>rsect,o. l ,.""t-s. h ., r: o.: ..... 1 e p u rpose ana use o r t.r:ese :.:: discuss:ri the n:xt sac":ion. Arriving at the Study Location W hen tile observer arri ves at the study location he should familiarize "ith it. i s this the intersection to be studied? Which approa c h l eg s :re to be used for conflict observations? many 1 a nes are there? Observation poi nts are selected next. The main objective is to select locations that. offer the observer a clear view of t h e i ntersection a n d traffic movements. For confl'ict observations, a location approximately 100 to 300 feet from the intersection and on the right side of the ap proach is usually best. The location depends on vehicle .speeds and approach geometry. i n figure 20 is an example of an intersection with the observer locations mark ed. In this example, the engineer had requested conflict counts be taken on the two nonstop sig n approaches. At high-speed locat ions, a location shou l d be p i c ke d farther away (300 feet or more) from the intersection so t ha t all actions and maneuvers re 1 at i ng to the intersection can be observed. In urban areas operating speeds are typically 25 mi/h, a shorter distance (100 feet or more) may be appropriate. The location of the observer position should be noted on the conflict form, especially if a before and after study i s planned for the intersection. To obtain accurate conflict counts, it is essential that the observer not influence passing motorists. Ideally, the observer and equipment should be i nvisible. The best practice is to blend into the natural background to become inconspicuous. Several suggestions are offered below. Often conflict observations can be made from the observer's vehic l e. The observer should always park his vehicle off the roadway unless on-street parking i s. permitted Figure 21 s hows a typical sHuati on where the 21


I I N 1 UC'$ 1:10. l l o.,.,,, Figure 20. Typical intersection diagram showing observer position s . cigure 21. Conflict observer 1n pickup parked on the intersection approach.


observers (;.ar i s parked on t h e stre-=: t i n front of One shouid neve:-use a vehicl e that could be mist. aken .fo. ra police or other official car tha:: would affect traffic behavior. Where on-street parki n g is permitted, a parki n g spot i s usually adequate provided that other ve hicles are par!

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