Fundamentals of Traffic Flow, Slides of Transportation Engineering

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PRINCIPLES OF

TRANSPORTATION ENGINEERING

Fundamentals of Traffic Flow

FUNDAMENTALS OF TRAFFIC FLOW

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a. Theoretical Maximum Capacity in Vehicles per Hour

b. Braking Distance

c. Sight Distance

d. Stopping Distance

e. Stopping Distance (in terms of Acceleration)

f. Flow, density and speed

g. Peak Hour Factor

h. Time headway

i. Time Mean Speed

j. Space Mean Speed

k. Variance of the space distribution of speeds

l. Standard deviation of the space distribution of speeds

THEORETICAL MAX. CAP IN VEH/HR

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a. Theoretical Maximum Capacity in Vehicles per Hour

The theoretical maximum capacity in traffic flow refers to the highest number of

vehicles that can pass a point on a roadway within an hour under ideal conditions. This

concept is crucial for understanding and managing traffic congestion.

• 1. Sigua, Ricardo G. Fundamentals of Traffic Engineering. The University of the Philippines Press, 2008.
• 5.2: Traffic Flow - Engineering LibreTexts
• 7.1: Sight Distance - Engineering LibreTexts. Retrieved October 2024.
• https://eng.libretexts.org/Bookshelves/Civil_Engineering/Fundamentals_of_Transportation/07%3A_Geometric_Design/7.01%3A_Sight_Distance. Retrieved October 2024.

THEORETICAL MAX. CAP IN VEH/HR

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KEY POINTS

1. Ideal Conditions : Assumes perfect weather, no accidents, and optimal road

conditions.

2. Roadway Design : Influenced by lane width, number of lanes, and road geometry.

3. Traffic Control : Includes the impact of traffic signals, signs, and other control

devices.

4. Vehicle Types : Considers the mix of different vehicle types, such as cars, trucks,

and buses.

• 1. Sigua, Ricardo G. Fundamentals of Traffic Engineering. The University of the Philippines Press, 2008.
• 5.2: Traffic Flow - Engineering LibreTexts
• 7.1: Sight Distance - Engineering LibreTexts. Retrieved October 2024.
• https://eng.libretexts.org/Bookshelves/Civil_Engineering/Fundamentals_of_Transportation/07%3A_Geometric_Design/7.01%3A_Sight_Distance. Retrieved October 2024.

SIGHT DISTANCE

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c. Sight Distance

• This is the length of road visible to the driver. It ensures that drivers have enough

distance to see and react to any obstacles or changes in the road ahead.

• Types of sight distance include stopping sight distance, passing sight distance, and

intersection sight distance.

• 1. Sigua, Ricardo G. Fundamentals of Traffic Engineering. The University of the Philippines Press, 2008.
• 5.2: Traffic Flow - Engineering LibreTexts
• 7.1: Sight Distance - Engineering LibreTexts. Retrieved October 2024.
• https://eng.libretexts.org/Bookshelves/Civil_Engineering/Fundamentals_of_Transportation/07%3A_Geometric_Design/7.01%3A_Sight_Distance. Retrieved October 2024.

STOPPING DISTANCE

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d. Stopping Distance

• This is the total distance a vehicle travels before it comes to a complete stop,

combining both the perception-reaction time and the braking distance.

• Stopping Sight Distance (SSD) is a key measure, calculated as the sum of the

distance traveled during the driver’s reaction time and the braking distance. The

formula for SSD incorporates both the perception-reaction time and the braking

distance, which is influenced by acceleration (or deceleration).

• 1. Sigua, Ricardo G. Fundamentals of Traffic Engineering. The University of the Philippines Press, 2008.
• 5.2: Traffic Flow - Engineering LibreTexts
• 7.1: Sight Distance - Engineering LibreTexts. Retrieved October 2024.
• https://eng.libretexts.org/Bookshelves/Civil_Engineering/Fundamentals_of_Transportation/07%3A_Geometric_Design/7.01%3A_Sight_Distance. Retrieved October 2024.

FLOW, DENSITY AND SPEED

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f. Flow, density and speed

Traffic Flow (q) - number of vehicles passing through a point in the

roadway per unit of time.

- q (veh/hr)

Traffic Density (k) - Number of vehicles travelling per length of roadway.

- k (veh/km)

Speed (Space MS) - Length travelled over total time of travel

- μ s (km/hr)

q = μ

s

k

FLOW, DENSITY AND SPEED

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Space Headway - The distance between successive vehicles

moving in the same lane measured from

head-to-head at any instance.

Time Headway - The time interval between the passage of

successive vehicles moving in the same

lane measured from head-to-head as they

pass a point on the road

• 1. Sigua, Ricardo G. Fundamentals of Traffic Engineering. The University of the Philippines Press, 2008.
• 5.2: Traffic Flow - Engineering LibreTexts
• 7.1: Sight Distance - Engineering LibreTexts. Retrieved October 2024.
• https://eng.libretexts.org/Bookshelves/Civil_Engineering/Fundamentals_of_Transportation/07%3A_Geometric_Design/7.01%3A_Sight_Distance. Retrieved October 2024.

PEAK HOUR FACTOR

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g. Peak Hour Factor - The peak hour factor (PHF) is the hourly volume during

the maximum volume hour of the day divided by the

peak 15-minute flow rate within the peak hour, a

measure of traffic demand fluctuations within the

peak hour.

PHF =

DHV =

Note: The purpose of DHV (Design Hourly Volume of Approach) is to estimate the expected

volume that will flood the highway during peak hours.

• 1. Sigua, Ricardo G. Fundamentals of Traffic Engineering. The University of the Philippines Press, 2008.
• 5.2: Traffic Flow - Engineering LibreTexts
• 7.1: Sight Distance - Engineering LibreTexts. Retrieved October 2024.
• https://eng.libretexts.org/Bookshelves/Civil_Engineering/Fundamentals_of_Transportation/07%3A_Geometric_Design/7.01%3A_Sight_Distance. Retrieved October 2024.

PEAK HOUR FACTOR

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Sample Problem

The table shows a 15-minute volume counts

during the peak hour on an approach of an

intersection.

1. Compute the peak hour volume

2. Compute the peak hour factor

3. Compute the design hourly volume of

approach.

Time Volume of Traffic

6:00 – 6:15 PM 375

6:15 – 6:30 PM 380

6:30 – 6;45 PM 412

6:45 – 7:00 PM 390

• 1. Sigua, Ricardo G. Fundamentals of Traffic Engineering. The University of the Philippines Press, 2008.
• 5.2: Traffic Flow - Engineering LibreTexts
• 7.1: Sight Distance - Engineering LibreTexts. Retrieved October 2024.
• https://eng.libretexts.org/Bookshelves/Civil_Engineering/Fundamentals_of_Transportation/07%3A_Geometric_Design/7.01%3A_Sight_Distance. Retrieved October 2024.

TIME MEAN SPEED, SPACE MEAN SPEED

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j. Space Mean Speed (μs)

• Speed taking into account a segment of the roadway

• Harmonic mean of the speeds

• Average speed

μs =

• 1. Sigua, Ricardo G. Fundamentals of Traffic Engineering. The University of the Philippines Press, 2008.
• 5.2: Traffic Flow - Engineering LibreTexts
• 7.1: Sight Distance - Engineering LibreTexts. Retrieved October 2024.
• https://eng.libretexts.org/Bookshelves/Civil_Engineering/Fundamentals_of_Transportation/07%3A_Geometric_Design/7.01%3A_Sight_Distance. Retrieved October 2024.

TIME MEAN SPEED, SPACE MEAN SPEED

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Sample Problem

Two sets of students are collecting traffic data at two sections A and B of a

highway 200m apart. Observation at a shows that 4 vehicles passes that section

at intervals 0f 7.18 sec, 9.29 sec, 10.33 sec, and 12.68 sec.

a. Determine the time mean speed in kph

b. Compute the space mean speed at kph

• 1. Sigua, Ricardo G. Fundamentals of Traffic Engineering. The University of the Philippines Press, 2008.
• 5.2: Traffic Flow - Engineering LibreTexts
• 7.1: Sight Distance - Engineering LibreTexts. Retrieved October 2024.
• https://eng.libretexts.org/Bookshelves/Civil_Engineering/Fundamentals_of_Transportation/07%3A_Geometric_Design/7.01%3A_Sight_Distance. Retrieved October 2024.

FREEFLOW SPEED AND JAM DENSITY

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Relationship between free flow and jam density.

• 1. Sigua, Ricardo G. Fundamentals of Traffic Engineering. The University of the Philippines Press, 2008.
• 5.2: Traffic Flow - Engineering LibreTexts
• 7.1: Sight Distance - Engineering LibreTexts. Retrieved October 2024.
• https://eng.libretexts.org/Bookshelves/Civil_Engineering/Fundamentals_of_Transportation/07%3A_Geometric_Design/7.01%3A_Sight_Distance. Retrieved October 2024.

FREEFLOW SPEED AND JAM DENSITY

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Sample Problem

Two platoons of cars are timed over a distance of 0.5 km. Their flows are recorded.

The first group is timed at 40 seconds, with the flow at 1350 vehicles per hour. The

second group took 45 seconds , with a flow of 1800 vehicles per hour.

a. Determine the free flow speed in kph

b. Determine the jam density in veh/km

c. Determine the maximum flow of the traffic stream in veh/hr.

• 1. Sigua, Ricardo G. Fundamentals of Traffic Engineering. The University of the Philippines Press, 2008.
• 5.2: Traffic Flow - Engineering LibreTexts
• 7.1: Sight Distance - Engineering LibreTexts. Retrieved October 2024.
• https://eng.libretexts.org/Bookshelves/Civil_Engineering/Fundamentals_of_Transportation/07%3A_Geometric_Design/7.01%3A_Sight_Distance. Retrieved October 2024.