Week 5 - Models in Transp & Basic transp concepts and measures Flashcards

1
Q

What are models in transp?

A
  • models of physical transp system prominent part of transp planning tool kit
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2
Q

What are the types of models in TP?

A

i. diagrams
ii. physical models
iii. virtual models
iv. data models
v. GIS models
vi. framework models

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3
Q

Explain diagram models in TP

A
  • 2D, elevations, cross sections

- considers flows of traffic (modes; #bike and auto lanes; auto, pedestrian, bike counts; directions of travel)

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4
Q

Explain mathematical models in TP

A
  • express relationships mathematically
  • general function relationship
  • x explanatory, y is response
  • ex. forecasting, regression
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5
Q

Explain network models in TP

A
  • foundations of transp modelling and analysis are interconnected networks
  • multiple ways to travel b/w nodes (redundancy)
  • nodes and links
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6
Q

What are nodes and links?

A

Nodes: network locations, like airports, parking lots, intersections
Links: enable connections b/w nodes, like highways, airways, railways, etc.
- key consideration for both links and nodes is capacity

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7
Q

What are basic transp measures?

A
  • capacity (C)
  • throughput (Q)
  • demand (D)
  • density
  • speed (V)
  • design speed
  • reliability
  • safety
  • environmental performance
  • sustainability performance
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8
Q

Explain measure of capacity

A

Max number of units processed in unit of time

- ex. people/hr, vehicles/day, etc.)

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9
Q

Explain measure of throughput

A

Actual flow/volume of units in given time

  • relates to productivity of infrastructure
  • ex. people/hr, tonnes/hr, etc.
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10
Q

Explain measure of demand

A

Number of units desired per unit of time

  • reflects collective decisions (actual and latent)
  • latent demand (desire we’re currently unable to satisfy)
  • typically, Q =< C
  • if D > C, then Q = C
  • if D < C, then Q = D
  • expressed per time unit U (utilization)
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11
Q

What is utilization?

A

the percentage of capacity that is represented by throughput

  • often depends on perspective (Ex. busy side of highway has better utilization than empty in service provider’s perspective, but opposite from user perspective)
  • therefore, usually provide 85th percentile b/c good tradeoff b/w average and max
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12
Q

What is an alternative measure of utilization? (equation)

A

Volume capacity ratio (V/C)= (Q(people/hr))/(C(people/hr))

  • critical factor in any capacity analysis is proportion of facility’s capacity being utilized by current or projected traffic
    1. below capacity (v/c less than 0.75)
    2. approaching capacity (v/c ratio 0.75-1.0)
    3. exceeding capacity (v/c ratio greater than 1.0)
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13
Q

What is the key consideration in planning for networks?

A
  • usage level the network is designed for (avg, max, 85th)

- balancing costs with levels of service

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14
Q

Explain measure of density

A

Amount of activity per unit area

Density = activity or items/area

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15
Q

Explain measure of speed

A

aka velocity
V = distance/time
- looking at range of speeds important, not just determining average speed
- max depends on physical and legal limitations

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16
Q

Explain measure of design speed

A

Design physical system to encourage travellers to travel at design speed (road geometry)
- wide curves/lanes for higher speed and tighter for lower

17
Q

Explain measure of reliability

A

Commonly used in reference to the level of consistency in transp service for a mode, trip, route, or corridor for period of time (making trip on time, every time)

  • people remember when travel times take longer due to unexpected delays
  • just in time (JIT) production depends on reliable delivery times (scheduled economy)
18
Q

What factors influence reliability?

A
  1. incidents: collisions, break downs, disruption of normal traffic flow
  2. work zones: construction/maintenance
  3. weather: full range of events - low visibility from fog, rain, snow, sun in eyes
  4. fluctuations in demand: day-to-day variations caused by changes in activity levels (ex. weekends)
  5. special events: cause dramatically different travel patterns/volumes in vicinity
  6. traffic control devices: poorly timed signals or periodic signal events (ex. railroad crossing)
  7. inadequate base capacity: normally congested roads more susceptible to effects of other factors
19
Q

What are some approaches to measuring reliability?

A
  • probability that actual minus expectation is less than a certain threshold over certain percentage of time (threshold depends on trip purpose and how willing you are to accept being late)
  • buffer time index: represents extra time that travellers must add to their avg travel time to ensure on-time arrival
20
Q

Explain measure of safety

A

Measure frequency of accidents per person and the distance they travel
- depends on amt of driving/travelling you do to establish risk exposure
(# injuries OR # property damage OR # fatalities)/(person/km OR vehicle/km)

21
Q

Explain measure of environmental performance

A

Typically impact per unit of transp activity.

  • ex. emissions of GHGs
  • measure impacts based on transp output
  • carbon footprint calculator
  • most common effort is to reduce GHGs
22
Q

Explain measure of sustainability performance

A

3 pillars: social, economic, enviro

- driven by society b/c demands tied to liveability and health

23
Q

What are enviro principles under the sustainability performance for TP?

A
  • renewable, inexhaustible, recyclable resources should be favoured
  • transp with lower energy intensity should be favoured
  • emissions from vehicles that compromise air quality should be reduced
  • protect ecosystem integrity
24
Q

What are social principles under the sustainability performance for TP?

A
  • human health/safety promoted
  • everyone should have affordable and equitable access to jobs, schools, services, etc.
  • transp systems should be convenient, comfortable, sensitive to disabilities, etc. (generally people-friendly)
25
Q

What are economic principles under the sustainability performance for TP?

A
  • transp decisions should be compatible with society’s ability to pay for full costs (externalities)
  • supportive of vibrant economy
26
Q

Why are principles for selecting performance measures important?

A
  • connect to importance of monitoring and eval
  • regardless of transp system area planning and operations, performance measures and indicators matter
  • key role in decision making, understanding and communicating with stakeholders
27
Q

What are principles for selecting performance measures?

A
  • comprehensive: reflect various economic, social, and enviro impacts, and various transp activities
  • data quality: data collection practices should reflect high standards to ensure accuracy
  • comparable: data collection should be standardized so results are suitable for comparison
  • easy to understand: indicators must be useful to decision makers and understandable by public
  • accessible/transparent: indicators and analysis details should be available for all stakeholders
  • cost effective: cost effective to collect
  • net effects: indicators should differentiate b/w net impacts and shifts of impacts to diff locations/times