The Dynamic Urban Model Transport and Urban Development John Swanson Steer Davies Gleave February 2004
Transport and the Economy What is the contribution of transport to a local or regional economy? What is its role in regeneration? What is the effect of specific schemes? Of area policies? What is the effect of Road Pricing? The two-way road effect. This has been widely researched – but the results are ambivalent.
Conventional Transport & Land Use Models Traditional transport models are almost exclusively equilibrium models which makes them technically very difficult. Classic four stage model Trip generation Distribution Mode choice Route assignment Then add land use effects …
The Dynamic Urban Model Draws on Forrester’s original Urban Dynamics work But this said nothing about transport Combines it with ideas from conventional transport modelling The logit model for choices Network modelling software Generalised cost, utility etc
Transport and the Economy Why should transport contribute? It must be because it affects ‘accessibility’ Access of employers to a suitable workforce Access of the workforce to suitable jobs Access of businesses to suppliers, markets and other businesses
Access and Attractiveness as Business Location Transport infrastructure - travel times Businesses Net business Workforce startup rate - + - + accessible accessible + businesses workforce + + attractiveness as a business location
Access and Attractiveness as a Place to Live travel times jobs per business + - Businesses accessible jobs + + attractiveness as place to live + Workforce Net migration rate
Competition for Land and Premises Workforce Businesses net migration net business rate startup rate attractiveness as a attractiveness as business location place to live + + - - availability of housing availability + business premises + developers - + - expectations for developers expectations business units for housing demand + + construction rate for + Construction rate for Business business premises new houses Housing + premises + + stock Land available - - for development
Access: The Congestion Feedback transport infrastructure - travel times + transport activity + + workforce businesses
Putting it together Transport transport investment + workforce infrastructure + elsewhere - travel times jobs in other locations + access to - + markets and - transport activity supply chain accessible workforce + + + - accessible + jobs + + + + net inward attractiveness Skilled attractiveness as as place to live migration workforce business location + + + + + - housing + availability + net business + Businesses startups in area availability - of units + - + Housing housing + stock Business + - + + construction & business unit Land available for units enhancement construction development rate + rate - - land-use policy
Transport Transport is spatial So the model must divide the urban area into zones Network effects We must represent movements through networks Congestion at a location is affected by and affects activity elsewhere Transport offers choices of route, mode, whether or not to travel etc So we need to represent these choices Preferences and habits vary We need to recognise different preferences among people & trip purposes Not all modes are available to everyone Car ownership varies and is growing Availability of licences, household size etc.
Transport Networks: Roads The road network is described in terms of links. Routes between each pair of zones are specified as sequences of links. Several routes may be available – the model is capable of modelling route choice dynamically as conditions change. Each link has characterising properties: Its length (km) The free-flow speed; The capacity (vehicles/hour) beyond which speeds will drop; Any additional fixed costs (eg road pricing). When flows exceed capacity, speed-flow curves are used to reduce speeds.
Transport Networks: Public transport The PT network is also described in terms of links, and routes between each pair of zones are specified as sequences of links. Each link has a number of properties: Its length (km) The free-flow speed; The service headway; The capacity of each vehicle; Access and egress times to/from the network; One-way fares; Interchanges; Additional mode penalties (eg to distinguish between modes)
Modelling choices: the Logit Model Logit models are widely used in transport to model choices. They relate the ‘utility’ of each available alternative to the probability of it being chosen: exp( U ) i P ( i ) exp( U ) j j It’s up to us how to define utility – but usually it’s a linear additive function of the attributes – cost, time etc. Much existing research exists on suitable parameter values to use.
Travel choices The hierarchy of choices available when considering travel between two zones: Begin Whether to travel at all Too far In range Choice of mode Choice of route Public transport Car Walk PT PT PT Route Route Route 2 Route 3 Route1 3 2 Route 1
The Deterrence Curve The whole choice structure is handled by a hierarchical logit model. Right at the top is the decision about whether or not to travel at all. This gives rise to a deterrence function, relating the cost of travel to the proportion of people will to accept the cost. For instance, from zone i: 1 0.8 Accessible workforce = 0.6 j 0.4 Workforce DF ( i , j ) 0.2 j 0 0 10 20 30 40 50 60 Drive time (minutes)
The logit model The logit model is instantaneous, assuming: Everyone has perfect knowledge of the alternatives; and They make their choices immediately But it’s well known neither of these is correct
A Dynamic Logit Model: Choice of Route target route shares Car route utility scaler beta Car route utilities actual route share change in share <Car travel to Car route work trips> generalised times base link times total trips on each link Time to adapt to network changes congestion function route times current link Capacity time times multiplier routes capacity capacity ratio Trips to work per Averaging period for hour work trips
Business Clusters + transport times Businesses + - + accessible - businesses + + attractiveness as business location The two loops capture the tension between the desire to be close to businesses and services, versus the congestion that results.
Applications of the Model
Applications of the model Hastings and Bexhill Highly controversial by-pass proposal Merseyside Light rail schemes North East England Area in economic decline – wish to demonstrate transport investment can kick- start the economy
Applications of the Model Location Workforce Jobs Zones Transport Hastings & H: 36,000 H: 33,000 17 GC from Bexhill transport B: 12,000 B: 13,000 model Merseyside 490,000 448,000 140 GC from transport model NE England 1,130,000 923,000 81 Full network Hypothetical 26,000 25,000 7 Full network Note: GC means Generalised Cost
Typical Outputs Year: 2011 Base Land Change % Change Release Jobs 893 1,094 201 22% Vacancies 58 82 24 42% Households 952 1,007 55 6% Workforce 1,115 1,184 69 6% Job seekers 197 89 -108 55% Car kms 5,495 6,176 681 12% Average 42.8 39.2 -3.6 -8.4% speed (km/h) Thousands
Typical Outputs (2) Year: 2011 Base Land Change % Change Release Trips per day Car 606 722 116 19% PT 129 155 26 20% Walk 101 135 34 34% Mode shares Car 72% 71% -1 PT 15% 15% 0 Walk 12% 13% 1
Typical Outputs: Network Plots
Typical Outputs: Analysis of Movements
Some Findings: the Effects of Reduced Transport Costs Commute distances rise quite rapidly Eg road improvements increase car mode share and average commute distance – may conflict with environmental objectives; Effect of specific schemes on job numbers can be small Eg +1,000 jobs in NE England from large package of measures Congestion tends to re-locate Other constraints may be more important Especially land – but it must be accessible Was transport a constraint in the first place? Eg in Merseyside the workforce > jobs, so recruitment was not really a constraint. New transport re-distributed recruitment patterns but did not increase jobs – but did increase employment in poor areas
Some Findings: the Effects of Road Pricing Tests of road pricing showed initial change in behaviour but people shifting travel-to-work patterns and modes to revert to car use But also a tendency to push economic activity outwards – increased sprawl? Retail is doubly hit - staff and customers Change of use in the charge zone as retail leaves
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