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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? Masters thesis Roads & Traffic Department of Civil

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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

29th ICTCT Workshop in Lund, Sweden on 20th – 21st October 2016

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  • 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

Agenda

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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
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Conflicts between vulnerable road users

A case study

Before After

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Conflicts between vulnerable road users

A case study

Conflict between a cyclist (2) from left and a straight going cyclist (1) before entering the T-junction. Conflict between a pedestrian (2) from right or left and a straight going cyclist (1) before entering the T- junction. Conflict between a pedestrian (2) from right or left and a straight going cyclist (1) when leaving the T- junction.

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Simultanious arrival:

Two or more road users arrive at the same conflict zone within 3.00 seconds. A potential for a serious conflict.

Measure of risk:

Conflict zone

Conflict risk = Serious conflicts Simultanious arrivals t2 – t1 ≤ 3.00 sec

How to define a serious conflict?

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How to define a serious conflict?

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  • Traditional time-based conflict technique
  • Distance parameter?

– TA – TTC – TET – TIT – PET – TAdv – T2 –

….

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How to define a serious conflict?

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  • Traditional time-based conflict technique
  • Distance parameter?

– TA – TTC – TET – TIT – PET – TAdv – T2 –

….

Collision course: TTCmin ≤ 1.00 sec Crossing course: T2,min ≤ 0.55 sec

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How to define a serious conflict?

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TTCmin = 0.66 sec T2,min = 0.12 sec Serious conflict

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How to define a serious conflict?

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T2,min = 1.20 sec No conflict

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How to define a serious conflict?

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TTCmin = 0.06 sec T2,min = 1.18 sec Serious conflict

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How to define a serious conflict?

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1 2 3 4 5 1 2 3 4 Time-to-Collision [sec] Time [sec] TTC T2

Collision course: TTCmin ≤ 1.00 sec Crossing course: T2,min ≤ 0.55 sec

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  • Cyclists and pedestrians are often seen in close interaction
  • Can easily adapt to changes in speed and direction
  • Expresses efficient traffic flow

A need for an alternative method?

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Is time span a usefull factor when assessing severity of conflicts between vulnerable road users?

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  • 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?

Visual assessment of conflict severity

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15 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

The Delphi method

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16 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)

The Delphi method

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The Delphi method

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0% 15% 54% 31% 0% 0% 77% 23% 0% 20% 40% 60% 80% 100% Runde 1 Runde 2

Round 1 Round 2 No interaction Early interaction Slight conflict Serious conflict

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The Delphi method

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0% 15% 54% 31% 0% 0% 77% 23% 0% 20% 40% 60% 80% 100% Runde 1 Runde 2

Round 1 Round 2 No interaction Early interaction Slight conflict Serious conflict

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The Delphi method

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0% 15% 54% 31% 0% 0% 77% 23% 0% 20% 40% 60% 80% 100% Runde 1 Runde 2

Round 1 Round 2 No interaction Early interaction Slight conflict Serious conflict

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The Delphi method

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0% 15% 54% 31% 0% 0% 77% 23% 0% 20% 40% 60% 80% 100% Runde 1 Runde 2

Round 1 Round 2 No interaction Early interaction Slight conflict Serious conflict

Consensus = Slight conflict

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  • 227 hours of video
  • 43,000 vulnerable road users:

– 24,000 cyclists – 19,000 pedestrians

  • 846 simultanious arrivals:

– Before: 372 – After: 474

Results obtained

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Period Number of serious conflicts Time-based Delphi Before 12 4 After 9

Time-based Both methods Delphi

18 3 1

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  • 227 hours of video
  • 43,000 vulnerable road users:

– 24,000 cyclists – 19,000 pedestrians

  • 846 simultanious arrivals:

– Before: 372 – After: 474

Results obtained

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Period Conflict risk* Time-based Delphi Before 3.2 1.1 After 1.9 0.0

*Pr. 100 simultanious arrivals

Time-based Both methods Delphi

18 3 1

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23 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

Results obtained

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24 Include other interaction parameters?

Reactions: Additional behaviour: Personal characteristics:

  • Accelerations
  • Gestures
  • Sex
  • Braking
  • Orientation
  • Age
  • Changing course
  • Body language
  • Disability
  • (Auditive contact)
  • Injury risk

Method development

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This project

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Method development

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

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26 Fixed group of 8-10 respondents:

– Familiar with the method – Reduce instructions and time usage

Conflict risk <=> Accident risk How are these measures related?

Method development

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

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

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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