TRAFFIC FLOW FUNDAMENTALS (NB-10) Flashcards
(28 cards)
is considered very difficult due to several factors that cause its
irregularity or unpredictability
TRAFFIC
These factors could be attributed to several events which could happen on the road:
-accidents
-stalled vehicles
-lane changing or swerving
-parking maneuvers,
-indiscriminate loading and unloading of public utility vehicles
is usually classified as either uninterrupted or interrupted
TRAFFIC FLOW
Flow occurring at long sections of road where vehicles are not required to stop by any cause external to the traffic stream is called
UNINTERRUPTED FLOW
flow occurring at intersections or driveways where vehicles are required to stop by any cause outside the traffic stream - such as
traffic signs (STOP or YIELD), traffic signal lights, etc. - is called
interrupted flow
Major Traffic Variables
Uninterrupted flow can be described using any of the following traffic variables:
A. Flow rate or volume
B. Speed
C. Density or concentration
is defined as the number of vehicles passing a point during a specified period of
time.
Flow Rate
is defined as rate of motion in distance per unit time
Speed
two types of speed
- time mean speed
- space mean speed
Also called spot speed, is simply the arithmetic mean of the speeds of vehicles passing a point within a given interval of time.
Time mean speed
spot speed can be reasonably measured if a point is approximately by a short distance, say ______ of road. This distance is normally called ________ in spot speed studies.
- 15-50m
- trap length
_________ is used to describe the rate of movement of a traffic stream within a given section of road. It is the speed based on the average travel time of vehicles in the stream within the section. It is also called the __________.
- SPACE MEAN SPEED
- HARMONIC MEAN SPEED
is defined as the number of vehicles in a given length of road at an instant point
in time.
DENSITY
density proves to be the most difficult or expensive to observe. ___________ is the most commonly used method to get its exact values
Aerial photography
is defined as the time interval between passage of consecutive vehicles at
a specified point on the road with a unit of time per vehicles.
Time headway
is the distance between two vehicles measure from the front bumper of a vehicle
to that of another.
SPACING
It can only be measure, however, if a detector is installed at a specific point on the carriageway. It is defined as the total
time of a detector is occupied divided by the total time of observation
Time occupancy
as density increases, speed _______
decreases
the density corresponding to zero speed will be called________ and the speed corresponding to zero density will be
called ________
- jam density (kj)
- free flow speed (uf)
Theoretically, density is ______ since at least one vehicle must be present.
not zero
is defined as the maximum hourly rate at which persons or vehicles can reasonably be expected to transverse a point or uniform section of a lane or roadway during a given time period under prevailing roadway, traffic, and control conditions.
Capacity
is a qualitative description of how a certain
facility is performing.
LEVEL OF SERVICE (LOS)
rely on capacity and level of service analyses to determine the width and number of lanes when planning for new facilities or when expanding existing facilities that are already experiencing congestion problems.
Traffic Engineers
The __________ developed by Planning Service of the DPWH provides a methodology to carry out the process of such analysis.
Philippine Highway Planning Manual (PHPM)
