System Dynamics Evaluation of Traffic Safety Policy: An Exploratory Study

Transcription

1 System Dynamics Evaluation of Traffic Safety Policy: An Exploratory Study Dr. Yang Goh, Brett Hughes, Prof. Peter Love and Dr. Krassi Rumchev Curtin-Monash Accident Research Centre (C-MARC) School of Public Health, Faculty of Health Sciences Overview Traffic Safety as a Wicked Problem System Dynamics for Traffic Safety Case Study Discussioni

2 Purpose To assess the strengths and weaknesses of system dynamics methodology in the context of road safety ypolicy analysis Wicked Problems The search for scientific bases for confronting problems of social policy is bound to fail, because [they] are wicked problems Rettel and Webber (1973) Rettel, H. W. J., and M. M. Webber Dilemmas in a general theory of planning. Policy sciences 4:

3 Wicked Problems no enumerable set of potential solutions no stopping rule planner has no right to be wrong unique can be explained in numerous ways no opportunity to learn by trial-and-error symptom of another problem no immediate and no ultimate test of a solution no definitive iti formulation not true-or-false, but good-or-bad Traffic Safety is Wicked! Fatality Rate Driver behaviour Safety of vehicle Safety of roads Enforcement Education Encourage sale of ANCAP rating Frequency of maintenance

4 Traffic Safety is Wicked! Working hours Fatality Rate Driver behaviour Safety of vehicle Safety of roads Enforcement Education Encourage sale of ANCAP rating Frequency of maintenance If fatality rate increases the real reason is always debatable Traffic Safety is Wicked! Fatality Rate Driver behaviour Safety of vehicle Safety of roads Perceived Risk Policy resistance may occur!

5 System Dynamics A set of modelling tools to facilitate understanding of the real world Emphasise interactions or feedback between agents/ components across time 9 System Dynamics MIT- Forrester (1961) Applied in: Climate change (LTG Meadows et al. 2004) Supply chain Ecology Marketing Public health Project management Strategic planning Public policy 10

6 SD Method (Sterman 2000) Scenario specification Policy design What if Sensitivity analysis Cross policies analysis 1. Problem and scope Theme selection Key variables Time Horizon Reference modes Compare with reference mode Extreme conditions Sensitivity analysis 5. Policy design and evaluation 4. Testing 3. Formulation 2. Dynamic hypothesis Hypothesis Endogenous focus Mapping (causal loop diagram etc.) Stocks and flows simulation (structure, decision rules, parameters, relationships, initial conditions) 11 SD in Transport Policies Growing interest ASTRA project in Europe ( ) Environmentally Friendly Urban Transport System (Han et al. 2010) Impact assessment in the automotive industry (Walther et al. 2010) Land use transport interaction modelling (Pfaffenbichler et al. 2010)

7 SD in Traffic Safety Policy Traffic Safety Policy taker An externality dealt with after implementation of transport policy Possible applications of SD Understand effect of transport policies on traffic safety Analyse policy scenarios for traffic safety policies Safe System Fundamental Objectives making the road transport system more forgiving of human error minimising the level of unsafe road user behaviour System Dynamics facilitates safe system Bigger picture view; multiple stakeholders view Allows trial and error and theorising about possible effects Not a silver bullet

8 Case Study Case study is a platform for discussion Hypothetical case study Policy goal: Increase the average ANCAP rating of passenger cars on the road to 4-star by 2020 Key Assumptions: Only 3-star and 5-star cars Only network effect and price effects Group Model Building Cavana and Adams

9 Qualitative Models Amalgamation of mental models Sale of 3-Star Cars Scrapped Market Share for Network effect for Relative attractiveness of Price of 3-star Cars Demand for cars Market Share for 5-Star Cars Relative attractiveness of 5-Star Cars Pi Price of f5st 5-Star Cars Sale of 5-Star Cars Network effect for 5-Star Cars 5-Star 5Star Cars 5-Star Cars Scrapped System Dynamics Simulation Qualitative models are translated into quantitative model Most useful when there are large number of effects Relative strength of effects is unknown Complex inter-dependencies are likely Robust regression equations or expert opinions are available

10 Stocks 5-Star Cars ra_sx_slx_07.htm e-offers/commodore-international-?region=national Stocks 9,000, Cars Initial

11 Flows 136, Cars/month 75, Cars/month New Scrap Outflow 3-star mean lifetime mo 75, Cars/month Scrap '' '3-star mean lifetime'

12 Inflow Network Effect 136, Cars/month Social norm, 3-Star cars are good enough, no need to buy 5-star New Reinforcing Loop Market_share_3_st ar 8.62 Attractiveness_3- star Effect of 3-star stock on attractivenes Inflow Network Effect Based on Sterman (2000, 394) e N star Sensitivity ( )] Threshold [ 3 Threshold_For_Net work_effects 8,000,000.00, Cars 9.49 Sensitivity to size of car population 2.00 Effect of 3-star stock on attractivenes

13 9,000, Cars 3-star mean lifetime mo Three-Star Cars Initial 136, Cars/month 75, Cars/month Threshold_For_Net work_effects 8,000, Cars 2.00 New Scrap 9.49 Sensitivity to size of car population Effect of 3-star stock on attractivenes Threshold_for_price _effect Market_share_3_st ar Attractiveness_3- star 0.09 Sensitivity_Of_Attra ctiveness_to_priceto Price of 3-Star cars 0.20 Scrap Demand for cars 9.99 Effect_of_other_facto rs_on_attractiveness _3-star Effect of price of 3- star on attractiveness 23, AUD Mkt price of 3-star Govt tax on 3-star Baseline demand for cars Total_attractivenes s Scrap 5-Star Cars Sensitivity Analysis Sensitivity analysis - variation of 'Average Star Rating' with normally distributed 'Threshold h for network effect' (10% std. dev.) Avera age star rat ting % confidence bound % confidence bound month Non-commercial use only!

14 Policy Experimentation Threshold_For_Network_Effects Govt tax on 3-star (%) 1,000,000 3,000,000 5,000,000 7,000,000 9,000,000 Cars Non-commercial use only! Sensitivity to size of car population Non-commercial use only! Policy goal: To increase the average star rating to 4.0 at the end of 10 years Non-commercial use only! Govt subsidy on 5-star (%) Avg_star_rati ng 5-Star Cars Non-commercial use only! Policy Experimentation

15 Cost-Benefit Analysis AUD 60,000,000,000 30,000,000,000 Tax collected Cost of subsidy Non-commercial use only! Discussion System dynamics has significant potential Allows modelling of soft variables ( behavioural economics ) Ability to represent wicked problems and facilitate trial and error Collaborative approach

16 Discussion Level of Analysis More suitable for high level (macro or meso) analysis Validity Rigorous validity is impossible to achieve in wicked problems Key question is usefulness in solving wicked problems Discussion Size of model Blackbox effect can occur if model is too complex Replicate-the-real-world approach has to be avoided Capture key dynamics and levers

17 Any Questions? Thank you! Dr. Yang Goh, Brett Hughes, Prof. Peter Love and Dr. Krassi Rumchev Curtin-Monash Accident Research Centre (C-MARC) School of Public Health, Faculty of Health Sciences