1. Introduction Traffic flow characteristics
Variables: Volume speed, density, headway, gap, etc.
Mathematical distribution
Relationship bet. variables
Associated analytical techniques
Demand/capacity analysis, queuing analysis,
Traffic flow models, shockwave analysis, simulation, …
Planning, design, and operation
672: planning
625 traffic engineering: design
635 street and highway design
Variable: describe, quantify, relationship
Planning application: speed-volume relationship=>travel time=>traffic assignment
Design: volume=># lanes, type of facility
Operations: LOS, etc.

2. Types of Flows/Facilities
Uninterrupted Flow (Facilities)
Traffic flow is not affected by factors external to flow itself. Facilities have no fixed causes of delay or interruption external to the traffic stream.
Delays mainly due to congestion from high flow
E.g., freeways, multilane highways, rural two-lane highways
CVEN 617

3. Types of Flows/Facilities
Interrupted Flow (Facilities)
Traffic flow is affected by external factors, particularly traffic signals. Facilities have signals, STOP or YIELD signs, or other fixed, external causes of periodic delays or interruptions to the traffic stream
Control delay involved
E.g.,, signalized/unsignalized at-grade intersections, arterials, and urban street network
CVEN 618

4. Macroscopic vs. Microscopic
They are different methods to describe traffic variables such as speed, flow, density (or occupancy), headway, gap, etc. and the relationship among them
Macroscopic
Microscopic
Mesoscopic
Homework problem: What is a mesoscopic model?

5. Macroscopic Traffic stream Averages or aggregated measures
Measures/variables:
Average speed
Flow rate/volume
Density
Lane occupancy
Application example: traffic stream models; capacity analysis

6. Microscopic Dealing with individual vehicles
Dealing with subject vehicles interactions with its leader, follower, the vehicles next to it in adjacent lanes, …
Measures/variables:
Individual speed
Headway
Spacing
Gap
Application examples: car-following and lane change models; gap acceptance analysis

7. Demand versus Capacity
Demand: number of units that would like to be served per unit time
E.g., number of vehicles that approach/try to use a section of highway
Capacity (supply): number of units that can be served per unit time
Volume or flow: number of units that are actually being served per unit time
Can demand>capacity?
Can volume>capacity?
Can volume>demand? Trick question.

8. Flow Conditions/Types of Operation
D/C=0
Free-flow
Uncongested flow
Unstable flow
Forced flow
Congested flow
Breakdown
System failure
D/C=1
What is the v/c value?
Ask somebody to draw D/C vs. speed and v/c versus speed curves?
D/C>1
What are the v/c values?

9. Part I Traffic Flow Characteristics
Definitions
States
Mathematical distributions

10. Part II Traffic Analysis Techniques

11. Traffic Analysis Techniques
Why We Need to Analyze Traffic?
Assess or predict flow performance
Speed or density
Delay or queue
Identify critical/special flow conditions
Breakdown
Special events
Congestion

12. Types of Analysis Performance and Safety Analysis Capacity Analysis
Measuring and analyzing traffic and crash characteristics
Capacity Analysis
Estimating capacity=f (roadway, traffic, control)
Level of service=f(flow level, roadway, traffic, control)
Demand-Capacity Analysis
Adjust link traffic demand when demand>capacity
Queueing/Shock Wave Analysis
Traffic performance for a given demand (often demand>capacity)
Simulation Modeling
All of the above

13. Traffic Analysis Techniques
Time-Space Diagram
Queuing Analysis
Capacity Analysis
Traffic Flow (Stream) Models
Continuum Flow Models
Shockwave Analysis
Simulation       

14. TSD and Traffic Variables
Distance x
headway
spacing
Flow
density
Time t

15. Deterministic Queuing
arrival l
Slope: flow rate 1
Cumulative vehicles
Point of queue
accumulation m2
Point of queue
dissipation
Waiting time(delay) 1
Queue length
departure m1 1
Time

16. Stochastic Queueing Example: M/M/1
Traffic Intensity:
Average Queue Length:
Average Waiting Time:
Average time in system :

17. What is capacity, what is LOS?
Capacity Analysis
What is capacity, what is LOS? q v v1
LOS v2 q2 q1
qmax
capacity

18. Traffic Stream Models Example: Greenshields’ model
Linear relationship bet. u and k
Boundary conditions:
Flow is zero at zero density
Flow is zero at max. density (kj)
Free-flow speed (uf) at zero density
Flow-density curves are convex k u uf kj

19. Continuum Flow Models
Associate vehicular traffic as a stream or a continuum fluid
Traffic stream treated as a one-dimensional compressible fluid, hence the two assumptions:
Traffic flow is conserved
There is a one-to-one relationship between speed and density or between flow and density

20. Shock Wave Analysis

21. Simulation Models Why simulation? Pros? Cons? Like it or hate it? ???…

22. New Era of Transportation
Connected and autonomous vehicles
New data, new sensors, and new services
Big data and data analytics
Impact on traffic analysis