Relevant transportation topics covered in class · Traffic Control and Analysis at Signalized Intersections Signals offer the maximum degree of control at intersections. They relay messages of both what to do and what not to do. The primary function of any traffic signal is to assign right of way to conflicting movements of traffic at an intersection, and it does this by permitting conflicting streams of traffic to share the same intersection by means of time separation. By alternately assigning right of way to various traffic movements, signals provide for the orderly movement of conflicting flows. They may interrupt extremely heavy flows to permit the crossing of minor movements that could not otherwise move safely through the intersection. When properly timed, traffic signals increase the traffic handling capacity of an intersection, and when installed under conditions that justify its use, it is a valuable device for improving the safety and efficiency of both pedestrian and vehicular traffic. In particular, signals may reduce certain types of accidents, most notably the angle (broadside) collision. Green time. The amount of time within a cycle for which a movement or combination of movements receives a green indication (the illumination of a signal lens). This is expressed in seconds and given the symbol G. Yellow time. The amount of time within a cycle for which a movement or combination of movements receives a yellow indication. This is expressed in seconds and given the symbol Y. This time is referred to as the change interval, as it alerts drivers that the signal indication is about to change from green to red. Red time. The amount of time within a cycle for which a movement or combination of movements receives a red indication. This is expressed in seconds and given the symbol R. All-red time. The time within a cycle in which all approaches have a red indication (expressed in seconds and given the symbol AR). This time is referred to as the clearance interval, because it allows vehicles that might have entered at the end of the yellow interval to clear the intersection before the green phase starts for the next conflicting movement(s). This type of interval is becoming increasingly common for safety reasons because the rate of vehicles entering at the end of the yellow and beginning of the red indication has steadily increased in recent years. Pretimed. A signal whose timing (cycle length, green time, etc.) is fixed over specified time periods and does not change in response to changes in traffic flow at the intersection. No vehicle detection is necessary with this mode of operation. Semi-actuated. A signal whose timing (cycle length, green time, etc.) is affected when vehicles are detected (by video, pavement-embedded inductance loop detectors, etc.) on some, but not all, approaches. This mode of operation is usually found where a low-volume road intersects a high- volume road, often referred to as the minor and major street ...

1. Relevant transportation topics covered in class
· Traffic Control and Analysis at Signalized Intersections
Signals offer the maximum degree of control at intersections.
They relay messages of both what to do and what not to do. The
primary function of any traffic signal is to assign right of way
to conflicting movements of traffic at an intersection, and it
does this by permitting conflicting streams of traffic to share
the same intersection by means of time separation.
By alternately assigning right of way to various traffic
movements, signals provide for the orderly movement of
conflicting flows. They may interrupt extremely heavy flows to
permit the crossing of minor movements that could not
otherwise move safely through the intersection.
When properly timed, traffic signals increase the traffic
handling capacity of an intersection, and when installed under
conditions that justify its use, it is a valuable device for
improving the safety and efficiency of both pedestrian and
vehicular traffic. In particular, signals may reduce certain types
of accidents, most notably the angle (broadside) collision.
Green time. The amount of time within a cycle for which a
movement or combination of movements receives a green
indication (the illumination of a signal lens). This is expressed
in seconds and given the symbol G.
Yellow time. The amount of time within a cycle for which a
movement or combination of movements receives a yellow
indication. This is expressed in seconds and given the symbol
Y. This time is referred to as the change interval, as it alerts
drivers that the signal indication is about to change from green
to red.
Red time. The amount of time within a cycle for which a
movement or combination of movements receives a red
indication. This is expressed in seconds and given the symbol

2. R.
All-red time. The time within a cycle in which all approaches
have a red indication (expressed in seconds and given the
symbol AR). This time is referred to as the clearance interval,
because it allows vehicles that might have entered at the end of
the yellow interval to clear the intersection before the green
phase starts for the next conflicting movement(s). This type of
interval is becoming increasingly common for safety reasons
because the rate of vehicles entering at the end of the yellow
and beginning of the red indication has steadily increased in
recent years.
Pretimed. A signal whose timing (cycle length, green time, etc.)
is fixed over specified time periods and does not change in
response to changes in traffic flow at the intersection. No
vehicle detection is necessary with this mode of operation.
Semi-actuated. A signal whose timing (cycle length, green time,
etc.) is affected when vehicles are detected (by video,
pavement-embedded inductance loop detectors, etc.) on some,
but not all, approaches. This mode of operation is usually found
where a low-volume road intersects a high- volume road, often
referred to as the minor and major streets, respectively. In such
cases, green time is allocated to the major street until vehicles
are detected on the minor street; then the green indication is
briefly allocated to the minor street and then returned to the
major street.
Fully actuated. A signal whose timing (cycle length, green time,
etc.) is completely influenced by the traffic volumes, when
detected, on all of the approaches. Fully actuated signals are
most commonly used at intersections of two major streets and
where substantial variations exist in all approach traffic
volumes over the course of a day
· Queuing Theory
It is important to realize that the primary function of a highway
is to provide mobility. This mobility must be provided with
safety in mind while achieving an acceptable level of

3. performance (such as acceptable vehicle speeds). Many of the
safety-related aspects of highway design were discussed in
Chapter 3, and focus is now shifted to measures of performance.
The analysis of vehicle traffic provides the basis for measuring
the operating performance of highways. In undertaking such an
analysis, the various dimensions of traffic, such as number of
vehicles per unit time (flow), vehicle types, vehicle speeds, and
the variation in traffic flow over time, must be addressed
because they all influence highway design (the selection of the
number of lanes, pavement types, and geometric design) and
highway operations (selection of traffic control devices,
including signs, markings, and traffic signals), both of which
impact the performance of the highway. In light of this, it is
important for the analysis of traffic to begin with theoretically
consistent quantitative techniques that can be used to model
traffic flow, speed, and temporal fluctuations. The intent of this
chapter is to focus on models of traffic flow and queuing, thus
providing the groundwork for quantifying measures of
performance
Flow is often measured over the course of an hour, in which
case the resulting value is typically referred to as volume. Thus,
when the term “volume” is used, it is generally understood that
the corresponding value is in units of vehicles per hour (veh/h).
The definition of flow is more generalized to account for the
measurement of vehicles over any period of time. In practice,
the analysis flow rate is usually based on the peak 15-minute
flow within the hour of interest..
Aside from the total number of vehicles passing a point in some
time interval, the amount of time between the passing of
successive vehicles (or time between the arrival of successive
vehicles) is also of interest. The time between the passage of
the front bumpers of successive vehicles, at some designated
highway point, is known as the time headway.