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.

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

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

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?

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

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

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.

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?

Part I Traffic Flow Characteristics Definitions States Mathematical distributions

Part II Traffic Analysis Techniques

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

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

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

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

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

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

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

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

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

Shock Wave Analysis

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

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