Big picture transport planning
When precision fails and approximation succeeds
Transport planning and models
• Transport planning - the operation, management and adjustment of the transport system
• Quantified techniques (analysis assessment and forecasting) are needed
• Models of different types are available to assist these processes
Problems
• Transport planning has not delivered on broader objectives
• One reason for this is the reliance on narrowly focused models
• Another reason is the failure to apply strategic techniques to assist in seeing the big picture
Results• The effect of current transport modelling
efforts in NZ has been to perpetuate ‘business as usual’
• This means that most trends (emissions, delay, reliability, choice, accessibility, equity) will continue to move in the wrong direction
• New national targets for transport will not be achieved using current approaches
Does it have to be this way?
• No
• Providing there is a commitment to better analysis, assessment and forecasting
• Many techniques and models already exist – but they need to be well developed and appropriately applied
Conventional models (1)
• Conventional transport models may cover 3 stages: trip generation / attraction, trip distribution, and trip assignment. 4 stage models also have a mode split function.
• 3 and 4 stage models use distribution functions such as (Tij = αPiPj / Cn
ij).
• Responsiveness is often poor - induced or suppressed demand is not allowed for – and ‘implied elasticities’ may be weak
Conventional models (2)
• Conventional transport models are good at predicting ‘business as usual’ (expected land-use, population, car ownership and on the basis of current policies and prices)
• They are used to test policies, strategies, packages and programmes.
Conventional models (3)
• Many models are single stage and only deal with traffic engineering issues.
• Models are used to provide information for economic appraisal – the benefit cost ratio – very influential in decision making
• 1 stage models – often appear to be very precise – especially micro-simulation – very impressive visually and useful for sorting out some issues – but not all
Strategic gap
• Improvements in modelling are underway at the regional and local levels – although these will not cover all needs
• But there is currently a modelling ‘void’ at the inter-regional and national levels
• It takes time for a national modelling capability to be developed
Simplified demand modelling
• Conventional transport models are based on detailed representations of transport networks and on current behaviour
• Simplified demand modelling is much coarser grained but has more flexibility to consider behavioural responses – and could be said to represent ‘5th stage’ modelling
Strategy review model
• An example of a simplified demand model is the strategy review model (SRM) developed in 2008 in NZ
• SRM builds on current model outputs• Based on elasticities, cross elasticities,
diversion rates and impact factors• It has been applied at the local, regional
and national level for sensitivity testing and policy development purposes
Modelling Framework
© Copyright TFL 2008.
National & RegionalComparative Views
SRMUrban and
Metropolitan Model
SRMInter-Zonal
Model
SRMData Editor
Urban & MetLocation Modelling
Datasets
LocationResult
Datasets
SRMNational Compiler
Inter-ZonalLocation Modelling
Datasets
ProgrammeAssistance
SRM Urban and Metropolitan Models
Change in VehicleOperating Cost
Private Travel Cost
PT Cost
VKT Change
PT PatronageChange
Change in PT ServiceTDM Infrastructure
Level
Walking and CyclingTrips ChangeCO2 Change
Change in VehicleGeneralised Cost
Change in Fares
PT Service
VKT CongestionChange
VKT at E and F
VKT SOV ChangeVKT Network Speed Change
Car Driver Trips
Car Passenger Trips
Speed
HOV StrategyLevel
NM StrategyLevel
Diversion to Walking and Cycling
Diversion from TDM WC Impact
TDM WC Impact
% VKT at E and F % SOV ChangeAverage Network
Speed Change
Or
CO2 Per Capita
% VKT at E and FAverage Network Speed% SOV
WC Trips
WC Modeshare
CO2 Per Capita
Key
Regional Targets
National EstimateTargets
User Setting
Model Output
FareboxRecovery
ITS StrategyLevelRoad Supply
PT Modeshare
CongestionRate PT Patronage PT Modeshare
WC Trips
PT Patronage
SOV VKT per Capita
WC Trips
PT Patronage
Exit
Clickable map data loading
© Copyright TFL 2008.
Exit
Adjust model settings using sliders and drop
down selections
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Exit
Consolidated Views
ExitResults
summarised for modelled
periods
Targets, BAU and modelled
impact
Exit
Sample Comparative Views
Comparing regional outcomes
Walking and Cycling by Location PT Patronage by Location SOV VKT per capita by Location VKT at E and F by Location Speed by Location CO2 Volume by Location Per Capita Co2 by Location Per Capita PT Patronage by Location Per Capita VKT at E and F Per Capita Walking and Cycling Trips by Location PT Modesplit by Location Walking and Cycling Modesplit by Location Car Driver Modelsplit by Location Car Passenger Modesplit by Location Per Capita Co2 Target by Location Per Capita PT Trips Target by Location Per Capita Walking and Cycling Trips Target by Location
The future? (1)
• Role of mathematicians in supporting the development of new techniques - especially in the field of simplified demand modelling
• Especially in terms of how the robustness and validity of models can be improved
• One example, the treatment of arc-based elasticities.
The future? (2)
• Role of operational research in optimising target profiles.
• Maximising the good (public transport, walking and cycling)
• Minimising the bad (travel time variability, single occupant vehicles, emissions)
• Within given constraints – such as cost and funding
Public transport example