L2 Microscopic Traffic Flow Parameters

Apr 8, 20201 like591 views

This document defines microscopic traffic stream parameters such as speed, density, flow, time headway, space headway, and spacing. It establishes the relationships between these parameters and provides the basic traffic flow equation relating flow, density, and speed. Examples are also given to demonstrate calculating traffic flow parameters from given data.

Traffic Flow Characteristics
CIVL 4162/6162
(Traffic Engineering)

Lesson Objective
• Define microscopic traffic stream parameters
• Establish the relationship between traffic
stream parameters
• Calculate and compute parameters with given
data

Remainder
• Macroscopic traffic flow parameters
– Volume
• Rate of flow
• AADT
• AAWT
• ADT
• AWT
– Speed
– Density

Flow Density
veh/hr veh/mi
Measured over time at a fixed
point
Measured over space at a
fixed time
How many vehicles are
getting somewhere?
How crowded is the roadway?
Can measure with a point
detector
Can measure with an aerial
photo
q k
Traffic Flow Basics-Summary (1)

Individual vehicle Traffic stream
Speed [L/T]
Flow [V/T]
Density [V/L]
Traffic Flow Basics-Summary (1)

Individual vehicle Traffic stream
Speed [L/T]
Flow [V/T]
Density [V/L]
Classify the quantities
Brackets describe units... L = Length,
T = time, V = vehicles
Traffic Flow Basics-Summary (3)

Individual vehicle Traffic stream
Speed [L/T]
Time Headway [T] Flow [V/T]
Density [V/L]
Let’s try to fill in the rest of the table.
Traffic Flow Basics-Summary (4)

The time headway is the time between two vehicles passing a
point.
Time (t)
Distance(x)
Traffic Flow Basics-Time Headway

On a space-time diagram, it is the horizontal
distance between two adjacent trajectories
Time (t)
Distance(x)
Traffic Flow Basics-Space Headway

Individual vehicle Traffic stream
Speed [L/T]
Time Headway [T] Flow [V/T]
Space Headway [L] Density [V/L]
Let’s try to fill in the rest of the table.
Traffic Flow Basics-Summary (5)

The space headway is the distance between two
vehicles.
Time (t)
Distance(x)
Traffic Flow Basics-Space Headway (1)

On a space-time diagram, it is the vertical distance
between two adjacent trajectories
Time (t)
Distance(x)
Traffic Flow Basics-Space Headway (2)

Individual vehicle Traffic stream
Speed [L/T] Average Speed
[L/T]
Time Headway [T] Flow [V/T]
Space Headway [L] Density [V/L]
Let’s try to fill in the rest of the table.
Traffic Flow Basics-Summary

Basic Equation for Uninterrupted Flow:
q = ku (v = SD in your book)
where :
q = flow rate,vph or veh /h /ln
k = density, veh /mi or veh /mi/ln
u = space mean speed,mph

Figure 5.4 Relationships among Speed, Flow, and Density (Source: Used with permission of Transportation Research
Board, National Research Council, from Highway Capacity Manual, 3rd Edition, Special Report 209, pp. 1–7,
Washington DC, 1994.)

Three Parameters of Traffic Flow
 Macroscopic:
 Speed (V)
 Density (K)
 Flow (Q)
 Q= KV
Q
K
K
V
Flow (veh/hr) Q
Speed(miles/hr)V
Density (veh/mi)
Speed
(miles/hr)
Flow(veh/hr)

Spacing
• Spacing is defined as the distance between
successive vehicles in a traffic lane; measured
from common reference
– Front bumper or
– Front wheels
• Average spacing in a traffic lane is related to
density

Headway
• Headway is defined as the time interval
between successive vehicles as they pass along
a lane
• Also measured between common point of
reference

Example
• Traffic in an interstate at 7:15 AM is observed
to have spacing of 250 feet; and average
headway of 3 sec. Estimate
– Volume
– Density
– Speed

Example
A study of freeway flow at a particular site has
resulted in a calibrated speed-density relationship
as follows:
S= 57.5(1-0.008D)
For this relationship, determine:
a. Free-flow speed
b. Jam density
c. Speed-flow relationship
d. Flow-density relationship
e. Capacity
(Note the difference in notation)

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05 Welded Track (Railway Engineering Lectures هندسة السكك الحديدية & Dr. Wali...Hossam Shafiq I

This document summarizes information about welded railway tracks from a textbook chapter. It introduces welded joints and long welded rails (LWR) as ways to reduce the number of weak rail joints. LWR terminology like "breathing length" is defined. Continuous welded rails (CWR) that have no joints at all are also discussed. Theories for how LWR works are presented, including equations for calculating the force and amount of expansion/contraction based on factors like the coefficient of linear thermal expansion, modulus of elasticity, and breathing length of the rail. An example problem is referenced from the textbook.

05 Rail Joints (Railway Engineering Lectures هندسة السكك الحديدية & Dr. Walie...Hossam Shafiq I

The document discusses different types of rail joints used in railway tracks, including supported, suspended, bridge, welded, staggered, square, compromise, insulated, and switch expansion joints. It notes that welded rail joints are the strongest and most perfect type but require accommodating thermal expansion, and describes various rail welding methods like electric arc, oxyacetylene, flash-butt, and chemical thermit welding. The document also covers advantages of welded rails, theory of welded rails, and provides an example calculation for railway track construction.

05 Rails (Railway Engineering Lectures هندسة السكك الحديدية & Dr. Walied A. E...Hossam Shafiq I

The document summarizes key aspects of railway engineering as it relates to rails, including: - Standard rail sections used internationally and factors that influence rail selection. - Common rail tests like falling weight, tensile strength, and hammer tests. - Types of rail defects like wear, battering, hogging, and corrugation - their causes and remedial measures. - Methods to measure rail wear including weighing and laser profiling of rail sections.

04 Ballast (Railway Engineering Lectures هندسة السكك الحديدية & Dr. Walied A....Hossam Shafiq I

This document discusses railway ballast, including its definition, functions, types used in Saudi Arabia, requirements, gradation, cleaning, minimum depth, construction, and relationship with sub-ballast. It notes that crushed limestone is commonly used for ballast in central Saudi Arabia but can chemically bond, reducing elasticity. The document asks students to calculate the volume of ballast and sub-ballast needed for 1 km of track in KSA, and provides an assignment on sub-ballast specifications per AREMA standards.

04 Rail Sleepers (Railway Engineering Lectures هندسة السكك الحديدية & Dr. Wal...Hossam Shafiq I

This document discusses different types of rail sleepers used in railway engineering, including their requirements, classification, materials, and practices in Saudi Arabia. The main types are wooden, steel, and concrete sleepers. Wooden sleepers have a life of 10-12 years but are suitable for many conditions. Steel sleepers last longer at 20-25 years but are prone to corrosion and expensive. Concrete sleepers, increasingly used in Saudi Arabia, are durable with a life of 40-50 years and offer stability, insulation, and gauge control. They are manufactured using pre-stressed concrete and a carousel curing process in Saudi plants.

03 Train Resistance and Tractive Power (Railway Engineering Lectures هندسة ال...Hossam Shafiq I

02 Handout #1 (Railway Engineering Lectures هندسة السكك الحديدية & Dr. Walied...Hossam Shafiq I

02 Rail Transport Systems (Railway Engineering Lectures هندسة السكك الحديدية ...Hossam Shafiq I

02 Railway Terminology (Railway Engineering Lectures هندسة السكك الحديدية & D...Hossam Shafiq I

This document provides an overview of key railway engineering terminologies and concepts in 3 paragraphs: Railway track structures transfer load from rolling stock to the ground. There are two main types: ballasted tracks using crushed stone ballast and ballastless tracks. Rails are the main component of tracks and come in different profiles like flat foot and bullhead. Rail fastenings fix rails to sleepers. Sleepers support rails and transfer load to ballast. Rolling stock refers to any vehicles that run on tracks. The main types are locomotives, coaching stock for passengers, and goods stock for cargo. Locomotives provide motive power and come in diesel or electric models. Coaching stock includes passenger coaches and luggage v

01 Introduction (Railway Engineering Lectures هندسة السكك الحديدية & Dr. Wali...Hossam Shafiq I

This document provides an overview of CE 435 Railway Engineering course taught by Walied A. Elsaigh at King Saud University. The course covers topics such as train dynamics and energy, railroad track, railroad constructions and maintenance, railway yards and terminals, communication and signals, and railway safety. It also outlines the textbook, additional readings, assignments, exams, and grade distribution. Finally, it introduces the Saudi railway network which includes projects like the North-South Rail Project, Haramain High Speed Rail, and light rail systems in major cities.