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

Question 1

What are models in transp?

Answer 1

• models of physical transp system prominent part of transp planning tool kit

Question 2

What are the types of models in TP?

Answer 2

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

Question 3

Explain diagram models in TP

Answer 3

• 2D, elevations, cross sections

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

Question 4

Explain mathematical models in TP

Answer 4

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

Question 5

Explain network models in TP

Answer 5

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

Question 6

What are nodes and links?

Answer 6

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

Question 7

What are basic transp measures?

Answer 7

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

Question 8

Explain measure of capacity

Answer 8

Max number of units processed in unit of time

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

Question 9

Explain measure of throughput

Answer 9

Actual flow/volume of units in given time

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

Question 10

Explain measure of demand

Answer 10

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)

Question 11

What is utilization?

Answer 11

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

Question 12

What is an alternative measure of utilization? (equation)

Answer 12

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)

Question 13

What is the key consideration in planning for networks?

Answer 13

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

- balancing costs with levels of service

Question 14

Explain measure of density

Answer 14

Amount of activity per unit area

Density = activity or items/area

Question 15

Explain measure of speed

Answer 15

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

Question 16

Explain measure of design speed

Answer 16

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

Question 17

Explain measure of reliability

Answer 17

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)

Question 18

What factors influence reliability?

Answer 18

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

Question 19

What are some approaches to measuring reliability?

Answer 19

• 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

Question 20

Explain measure of safety

Answer 20

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)

Question 21

Explain measure of environmental performance

Answer 21

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

Question 22

Explain measure of sustainability performance

Answer 22

3 pillars: social, economic, enviro

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

Question 23

What are enviro principles under the sustainability performance for TP?

Answer 23

• 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

Question 24

What are social principles under the sustainability performance for TP?

Answer 24

• 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)

Question 25

What are economic principles under the sustainability performance for TP?

Answer 25

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

Question 26

Why are principles for selecting performance measures important?

Answer 26

• 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

Question 27

What are principles for selecting performance measures?

Answer 27

• 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