Can the Delphi method complement or replace time-based measuring of - PowerPoint PPT Presentation

29 th ICTCT Workshop in Lund, Sweden on 20 th – 21 st October 2016 Can the Delphi method complement or replace time-based measuring of conflicts between vulnerable road users? Master’s thesis Roads & Traffic Department of Civil Engineering Aalborg University Morten Lind Jensen Via Trafik Rådgivning mlj@viatrafik.dk 1

Agenda • Conflicts between vulnerable road users • How to define a serious conflict? • A need for an alternative method? • Visual assessment of conflict severity • The Delphi method • Results obtained • Method development 2 2

Conflicts between vulnerable road users A case study - Vulnerable road users: - Pedestrians - Cyclists (mopeds included) - Video based before and after study - Case study - Four T-junctions in Aalborg 3

Conflicts between vulnerable road users A case study Before After 4

Conflicts between vulnerable road users A case study Conflict between a Conflict between a Conflict between a cyclist (2) from left and pedestrian (2) from pedestrian (2) from a straight going cyclist right or left and a right or left and a (1) before entering the straight going cyclist (1) straight going cyclist (1) T-junction. before entering the T- when leaving the T- junction. junction. 5

How to define a serious conflict? Simultanious arrival: Two or more road users arrive at the same conflict zone within 3.00 seconds. A potential for a serious conflict. t 2 – t 1 ≤ 3.00 sec Conflict zone Measure of risk: Serious conflicts Conflict risk = Simultanious arrivals 6

How to define a serious conflict? • Traditional time-based conflict technique • Distance parameter? – TA – TTC – TET – TIT – PET – T Adv – T 2 – …. 7 7

How to define a serious conflict? • Traditional time-based conflict technique • Distance parameter? – TA – TTC Collision course: – TET TTC min ≤ 1.00 sec – TIT – PET Crossing course: – T Adv T 2,min ≤ 0.55 sec – T 2 – …. 8 8

How to define a serious conflict? TTC min = 0.66 sec T 2,min = 0.12 sec Serious conflict 9 9

How to define a serious conflict? T 2,min = 1.20 sec No conflict 10 10

How to define a serious conflict? TTC min = 0.06 sec T 2,min = 1.18 sec Serious conflict 11 11

How to define a serious conflict? 5 Time-to-Collision [sec] 4 Collision course: 3 TTC min ≤ 1.00 sec 2 Crossing course: T 2,min ≤ 0.55 sec 1 0 0 1 2 3 4 Time [sec] TTC T2 12 12

A need for an alternative method? • Cyclists and pedestrians are often seen in close interaction • Can easily adapt to changes in speed and direction • Expresses efficient traffic flow Is time span a usefull factor when assessing severity of conflicts between vulnerable road users? 13 13

Visual assessment of conflict severity • Definition of a serious conflict by visual assessment: A simultanious arrival where at least one of the road users make a hazardous reaction just prior to the conflict zone. • How to assess conflict severity? 14 14

The Delphi method The Delphi method in general: • Experts are consulted • Uncertainty regarding a given topic • Consensus building • Multible rounds of questioning • Distribution of responses are presented before next round 15 15

The Delphi method This Delphi study: • 30 experts (professionals with sound knowledge of traffic safety) • Assess conflict severity • Two rounds of questioning • 50 potential conflicts are categorized in four levels of interaction: 0. No interaction 1. Early interaction 2. Late interaction / Slight conflict 3. Breakdown / Serious conflict • Measuring consensus: IQR (Inter Quartile Range) 16 16

The Delphi method 100% 77% 80% 54% 60% Runde 1 Round 1 Runde 2 Round 2 40% 31% 23% 15% 20% 0% 0% 0% 0% No interaction Early interaction Slight conflict Serious conflict 17 17

The Delphi method 100% 77% 80% 54% 60% Runde 1 Round 1 Runde 2 Round 2 40% 31% 23% 15% 20% 0% 0% 0% 0% No interaction Early interaction Slight conflict Serious conflict 18 18

The Delphi method 100% 77% 80% 54% 60% Runde 1 Round 1 Runde 2 Round 2 40% 31% 23% 15% 20% 0% 0% 0% 0% No interaction Early interaction Slight conflict Serious conflict 19 19

The Delphi method 100% 77% 80% Consensus = Slight conflict 54% 60% Runde 1 Round 1 Runde 2 Round 2 40% 31% 23% 15% 20% 0% 0% 0% 0% No interaction Early interaction Slight conflict Serious conflict 20 20

Results obtained • 227 hours of video • 43,000 vulnerable road users: – 24,000 cyclists – 19,000 pedestrians Number of serious conflicts Period • Time-based Delphi 846 simultanious arrivals: Before 12 4 – Before: 372 – After: 474 After 9 0 Time-based Both methods Delphi 18 3 1 21 21

Results obtained • 227 hours of video • 43,000 vulnerable road users: – 24,000 cyclists – 19,000 pedestrians Conflict risk* Period • Time-based Delphi 846 simultanious arrivals: Before 3.2 1.1 – Before: 372 – After: 474 After 1.9 0.0 *Pr. 100 simultanious arrivals Time-based Both methods Delphi 18 3 1 22 22

Results obtained Consensus building: • Round 1: Consensus in 47 of 50 potential conflicts • Round 2: Consensus in all 50 potential conflicts Assessment of severity: • Based on visible reactions • No reaction  No conflict 23 23

Method development Include other interaction parameters? Reactions: Additional behaviour: Personal characteristics: - Accelerations - Gestures - Sex - Braking - Orientation - Age - Changing course - Body language - Disability - (Auditive contact) - Injury risk This project 24 24

Method development Full length of the conflict Trimmed conflict It went well … What happens next? 25 25

Method development Fixed group of 8-10 respondents: – Familiar with the method – Reduce instructions and time usage Conflict risk <=> Accident risk How are these measures related? 26 26

Can the Delphi method complement or replace time-based measuring of conflicts between vulnerable road users? 27 27

Can the Delphi method complement or replace time-based measuring of conflicts between vulnerable road users? 28 28

THANK YOU! Morten L. Jensen Traffic Planner Via Trafik Rådgivning mlj@viatrafik.dk Harry Lahrmann Associate Professor Aalborg University hsl@civil.aau.dk Tanja K.O. Madsen PhD Fellow Aalborg University tkom@civil.aau.dk 29