System Dynamics & Transportation

Or: You just have problems

1

Ann Terlaak Associate Professor

May 29th 2015

2

As  a  leader  in  public  health  [transporta3on],  you  do  not  face  health  [transporta3on]  problems,  financial  problems,  technical  problems,  and  community  related  problems.  You  just  have  problems.  (Sterman,  2006)        

Complex Systems “When  you  are  confronted  by  any  complex  social  system  …  with  things  about  it  that  you  are  dissa3sfied  with  and  anxious  to  fix,  you  cannot  just  step  in  and  set  about  fixing  with  much  hope  of  helping.  […]  You  cannot  meddle  with  one  part  of  a  complex  system  from  the  outside  without  the  almost  certain  risk  of  seKng  off  disastrous  events  that  you  hadn’t  counted  on  in  other,  remote  parts.  If  you  want  to  fix  something  you  are  first  obliged  to  understand…the  whole  system.  […]  Intervening  is  a  way  of  causing  trouble.”  (Thomas,  1974)  

3

Policy Resistance - Examples

•  Failure  of  Washington’s  conserva3on  program  designed  to  combat  erosion  and  help  the  environment  by  paying  farmers  to  take  soil  out  of  cul3va3on  for  a  decade:  For  every  eroding  acre  a  farmer  idled,  nearly  as  much  addi3onal  erosion  prone  land  was  plowed  up  (Business  Week,  3/18/96)  • U.S.  road  building  programs  designed  to  reduce  conges3on  have  increased  traffic,  delays,  and  pollu3on  (Sterman,  2000)      

4

Policy Resistance – Cause

Policy  resistance  arises  from  the  gap  between  the  complexity  of  the  systems  in  which  we  live  and  the  o^en  simplis3c  and  erroneous  mental  models  of  those  systems  that  guide  our  decisions  and  behavior.  (Sterman,  2012)  

5

A  method  to  enhance  learning  in  complex  systems  •  Moves  us  from  generaliza3ons  about  systems  thinking  to  tools  and  processes  that  help  us  understand  complexity,  design  beaer  opera3ng  policies,  and  guide  change  •  Feedback  is  one  of  the  core  concepts  of  system  dynamics;  causal  loop  diagramming  (CLD)  is  a  central  tool  to  map  the  feedback  structures  of  complex  systems  •  CLD  can  help  us  understand  how  policy  resistance  arises;  it  shows  how  policies  that  are  directed  at  the  symptoms  of  a  problem  o^en  trigger  compensa)on  feedbacks  that  undercut  the  intended  effects  of  the  policy    

6

System Dynamics

7

TravelTime

HighwayCapacity

TrafficVolume

RoadConstruction

DesiredTravel Time

Pressure toReduce

Congestion

B1

CapacityExpansion

Cars inRegion

Trips perDay

AverageTrip Length

Attractivenessof Driving

Populationand Economic

Activity ofRegion

Cars perPerson

Adequacy ofPublic Transit

PublicTransit

Ridership PublicTransit

Revenue

PublicTransit

Fare

PublicTransitCosts

PublicTransitDeficit

PublicTransit

NetworkMove to

the Burbs

Extra Miles

Take theBus?

Open theHinterlands

RouteExpansion

FareIncrease

CostCutting

Choke offRidership

Can't Get Thereon the Bus

+

-+

+

+

-

+++

-

+

+

++

+

+

-

- + -+

+

+

-+

+

+- -+

-

Delay

DelayDelay

Delay

B2

R1

B3

B5

B4

R3

R2

B7

R4

B6

Size of RegionWithin Desired

Travel Time

DiscretionaryTrips

MT CapacityExpansion

B8

-

Delay

(Sterman,  2000)  

CLD & Policy Resistance I

8

(Sterman,  2000)  

9

(Sterman,  2000)  

CLD & Policy Resistance II

10

(Sterman,  2000)  

CLD & Policy Resistance III

11

TravelTime

HighwayCapacity

TrafficVolume

RoadConstruction

DesiredTravel Time

Pressure toReduce

Congestion

B1

CapacityExpansion

Cars inRegion

Trips perDay

AverageTrip Length

Attractivenessof Driving

Populationand Economic

Activity ofRegion

Cars perPerson

Adequacy ofPublic Transit

PublicTransit

Ridership PublicTransit

Revenue

PublicTransit

Fare

PublicTransitCosts

PublicTransitDeficit

PublicTransit

NetworkMove to

the Burbs

Extra Miles

Take theBus?

Open theHinterlands

RouteExpansion

FareIncrease

CostCutting

Choke offRidership

Can't Get Thereon the Bus

+

-+

+

+

-

+++

-

+

+

++

+

+

-

- + -+

+

+

-+

+

+- -+

-

Delay

DelayDelay

Delay

B2

R1

B3

B5

B4

R3

R2

B7

R4

B6

Size of RegionWithin Desired

Travel Time

DiscretionaryTrips

MT CapacityExpansion

B8

-

Delay

(Sterman,  2000)  

Shepherd,  S.P.  (2014).  A  review  of  system  dynamics  models  applied  in  transporta3on.  Transportmetrica  B:  Transport  Dynamics,  Vol.2(2),  p.83-­‐105    

12

Literature SD & Transportation

13

Thank You!