Week 4 - Transportation Land Use Connection & 4 Step Transp Model Flashcards
What is accessibility?
Ability to reach desired goods, services, activities, and destinations (collectively called opportunities)
- access is ultimate goal of most transp
- most often associated with a location (combo of distances b/w locations and the opportunities there)
- values both mobility (people’s ability to travel) and land use patterns (location of activities)
- considers all modes as potentially important (value based on user needs)
- arguably the focus of TP
What is the transp-land use connection?
- land use is the fixed fabric of the city that allows for activities
- TP based on activities b/c it connects spaces
What is the difference between mobility and accessibility?
Mobility: what’s the mode? how do you get there? how fast?
Accessibility: where can you go? what can you get to? what’s the generalized cost?
What can accessibility be broken down into?
- Mobility (ability of user to move to reach destinations): capacity (total volume of infrastructure) & efficiency (effective use of capacity)
- Land Use Patterns (proximity to user of destinations): density (concentration of destinations), diversity (mix of destinations), & design (influence on modal choice)
- Mobility Substitutes (alts to movement, ex. online shopping)
What is the issue with mobility over accessibility?
The ease of movement can lead to undesirable results.
- high accessibility (generalized costs low) can be provided even with low mobility (transit, walk)
- where origins and destinations are spread broadly, even great mobility does not ensure high accessibility (generalized costs high) (drive)
What are the various meanings of accessibility depending on who you ask?
- engineers: access refers to connections to adjacent properties
- accessible design for disabilities
- social planning access to food and healthcare
What is Wegener’s theoretical land use transport feedback cycle?
- land use: establishes patterns of activity
- activity: drives demand for transport
- transport system: influences accessibility
- accessibility: influences land use/development/location decisions
More In-depth Version
Start point: construction
1. Locations of human activities determined by locations of households/land use distribution
2. Distribution of human activities in space requires spatial interactions/trip decisions to overcome distance b/w locations
3. Traveler decisions cause traffic flows and congestion
4. Travel times, trip lengths, and travel costs create opportunities for interactions, measured as access
5. Distributions of accessibility influences location decisions and results in changes of attractiveness and building stock
6. Changes in supply determine location/relocation decisions of households and firms - leads to more construction
What are link loads?
- basically, as travel time increase, there is exponential growth of the links (between locations), causing larger link loads
Why use the 4 step transp model (aka the UTMS - Urban Transp Modelling Sytsems)?
- used to analyze/forecast changes in transp demand
- future demand in short and long term models project pop growth = land use change = transp system demand change
- examine impact of proposed changes (ex. eliminating bridge), policy changes (ex. parking restriction), and fuel price changes
What are the fundamentals of (requirements for) the 4 step transp model?
Building blocks for model:
- land use info (lot size, building footprint use codes)
- transp system (capacities of road, transit, other)
- household data (socioeconomics/users - income, education, household structure, car ownership)
- employ zone framework to allows modelling - estaablish Transportation Analysis Zones (TAZ) (goal is to divide city into relatively homogenous units in terms of transp activity)
What are the four stages/steps of the UTMS?
- Trip generation
- to travel
- for a given trip purpose at a given time
- i need to… (work, shop, etc.) - Trip distribution
- destination
- where will I (work, shop, etc.)? - Modal choice
- mode
- how will i get there? - Trip assignment to network
- route
- which route will i take?
Explain the UTMS Trip generation step
- the number of trips beginning in a zone (trip production) influenced by number of houses, age, employment, income, auto ownership
- how many trips end in that zone (trip attraction) influenced by number of jobs, type of jobs, land use
What are the TG/TA equations?
TG = f(#houses, #employed persons, #school age children, auto ownership, income)
- ex. lots of trips by the employed and school aged but fewer trips by elderly
TA = f(#jobs, industry type, land use)
What modelling methods does the UTMS Trip generation step use?
- linear regression
- cross-classification method/trip rate method (basically a chart where appropriate box is marked - ex. variables auto ownership and family size)
What is the trip gen manual?
- looks at a place of a certain size to predict how much attraction there will be
Explain the UTMS Trip distribution step
- determine origin and destination zones of trips (ex. yes i shop, but where?)
What modelling methods does the UTMS Trip distribution step use?
- more difficult to model
- can use a trip matrix to map out origin and destination TAZ (linking production to attraction)
What is the general trend between number of trips and distance? What about with zone attractiveness?
- number trips decreases as distance between zones increases
- total trip cost, including tolls and parking, increasing also decreases number of trips
- number of trips increase with zone attractiveness (ex. high sq. footage of retail)
- can be more complicated than this though
What is the problem with UTMS Trip distribution step?
- all modes are lumped together by purpose, so issue for non-vehicular trips b/c distance affects trips very differently (ex. advantages for non-vehicle modes)
- many walking/biking trips are intra-zonal and difficult to model
What is the basic criteria to include in trip dist model?
- cost of trip (travel time, actual costs)
- attractiveness (quantity and desirability of opportunity
Explain the UTMS mode choice step
- what mode are they going to use?
- what is the likelihood of taking diff modes (probability)?
- decision based on availability of modes & generalized costs
What is generalized cost (GC)? What is equation?
- combo of time, money, etc. to form basis of mode choice
GC = VOT(sum of time components) + out of pocket expenses
where VOT is the value of time, depending on income level and trip purpose ($/min)
What is the transit GC equation?
GC = $ + (access time + wait time + in vehicle time + egress time) * VOT
Explain the UTMS traffic assignment step
- which route will trips take?
- based on shortest path algorithm (minimum path of distance/time and GC)
- aka all-or-nothing method: assumes travellers want to use minimum impedance route b/w two points & all drivers will use fastest route w/o regard to congestion by other vehicles (load people onto link A until slows down then onto link B, etc.)
- “link” travel time is focus (function of distance, capacity, traffic volume, and speed)
What are the capacity restraints of minimum path?
- based on finding that as traffic flow increases, speed decreases
- there is relationship between impedance and flow for all types for highways
- assigns trips according to impedances coded on the links of the network
- attempts to balance the assigned volume, capacity of facility and related speed
What are the uses of traffic assignment?
An analysis tool model output can be used to analyze many things.
Examples:
- proposed road improvement compared against existing
- proposed general plans/amendments compared to current plan
- traffic impacts due to site plans, zone changes, etc.
