DECCAN COLLEGE OF ENGINEERING & TECHNOLOGY
(A Unit of Deccan Group of Institutions)
A Self-Financed Muslim Minority Institution Established by Dar-us-salam Educational Trust
Approved by AICTE, New Delhi & Affiliated to Osmania University
Dar-us-salam, Aghapura, Hyderabad-500 001 (T.S.)
DEPT. OF COMPUTER SCIENCE AND ENGINEERING
IV-YEAR|VIII-SEM|CSE-A & B(2024-2025)
SUBJECT: ESSENTIALS OF ROAD SAFETY ENGINEERING(OE805CE)
Unit-V
TRAFFIC SIGNALS AND HIGHWAY APPURTENANCES
Need For Traffic Signals
Traffic signs provide valuable information to drivers and other road users.
They represent rules that are essential for the safety of the population.
Traffic signals help to communicate messages to drivers and pedestrians so that they can maintain order and
reduce accidents.
Neglecting traffic signals can be dangerous or sometimes even fatal
Most signs make use of pictures, rather than words, thus they are easy to understand and can be interpreted by
people who speak a variety of languages.
Therefore it is important that drivers are familiar with each sign regarding what it represents
Traffic signals are used to inform the other road users regarding the rules of driving.
Failing to obey traffic signals could result in a serious accident or a fine Fixed and vehicle actuated signals.
Fixed time signals are normally installed at the intersection of two major roads.
The signals will change even if no cars or pedestrians are present.
Fixed time signals are less efficient when traffic varies quite a bit through the day, but they are cost-effective
because detectors are not required.
Fixed-time signals are the rule in urban areas for reasons of regularity, network organization, predictability,
and reducing unnecessary delay.
Vehicle-Actuated Signals require actuation by a vehicle on one or more approaches in order for certain phases
or traffic movements to be serviced.
They are equipped with detectors and the necessary control logic to respond to the demands placed on them.
Vehicle-actuated control uses information on current demands and operations, obtained from detectors within
the intersection, to alter one or more aspects of the signal timing on a cycle-by-cycle basis.
Timing of the signals is controlled by traffic demand.
Variability allows the signal to allocate green time based on current demands and operations.
A proper clearance interval between the green & the red phases is also ensured.
The various advantages of actuated signals are stated below:
They can reduce delay (if properly timed).
They are adaptable to short-term fluctuations in traffic flow.
Usually increase capacity (by continually reapportioning green time).
Provide continuous operation under low volume conditions.
Especially effective at multiple phase intersections.
The main disadvantages are as follows :
➢ If traffic demand pattern is very regular, the extra benefit of adding local actuation is minimal, perhaps
non-existent.
➢ Installation cost is two to three times the cost of a pre-timed signal installation.
➢ Actuated controllers are much more complicated than pre-timed controllers, increasing maintenance
costs.
➢ They require careful inspection & maintenance to ensure proper operation.
➢ There are three basic types of actuated control, each using signal controllers that are somewhat
different in their design:
Semi-Actuated Control
Full-Actuated Control
Volume-Density Control
TYPES OF TRAFFIC SIGNALS
Traffic signals come in various types, each serving a specific purpose in managing traffic flow and ensuring
safety on roads. Here are some common types:
1.Standard Traffic Lights: These are the most common type of traffic signals, consisting of red, yellow, and
green lights. They regulate the flow of traffic at intersections.
2.Pedestrian Signals: These signals are designed specifically for pedestrians to safely cross roads. They often
include symbols such as a walking person (indicating it's safe to cross) and a hand (indicating it's not safe to
cross).
3.Bicycle Signals: Similar to pedestrian signals, bicycle signals are meant to facilitate the safe passage of
cyclists at intersections. They may have specific symbols or lights indicating when cyclists can proceed.
4.Vehicle-Actuated Signals: These signals are triggered by the presence of vehicles at an intersection. They
use sensors embedded in the road to detect vehicles and adjust signal timing accordingly.
5.Railroad Crossing Signals: These signals warn drivers of approaching trains at railroad crossings. They
typically include flashing lights, bells, and lowered gates to prevent vehicles from crossing the tracks when a
train is approaching.
6.Flashing Traffic Lights: Sometimes used in low-traffic areas or during off-peak hours, flashing traffic lights
operate in a flashing mode, indicating that drivers should proceed with caution.
7.Emergency Vehicle Preemption Signals: These signals prioritize the passage of emergency vehicles such as
ambulances, fire trucks, and police cars by temporarily changing traffic signal patterns to give them a clear
path through intersections.
8.Reversible Lanes Signals: In some urban areas, lanes of traffic may be reversible depending on traffic flow.
Signals indicate when lanes are open for traffic in a particular direction.
9.Variable Message Signs (VMS): While not traditional traffic signals, these signs provide information to
drivers about traffic conditions, lane closures, detours, and other relevant information.
10.Transit Priority Signals: These signals give priority to public transit vehicles such as buses, allowing them
to proceed through intersections ahead of other traffic to improve efficiency and reliability of public
transportation systems.
Each type of traffic signal plays a crucial role in managing traffic flow, improving safety, and optimizing
transportation systems.
FACTORS AFFECTING SIGNAL DESIGN
Several factors influence the design of traffic signals to ensure they effectively manage traffic flow, prioritize
safety, and accommodate the needs of road users. Here are some key factors:
1.Traffic Volume: The volume of traffic at an intersection is a primary factor in determining signal design.
High-traffic intersections may require more complex signal timing patterns and larger signal heads to ensure
visibility.
2.Intersection Geometry: The layout of the intersection, including the number of lanes, turning lanes, and
pedestrian crossings, influences signal design. Complex intersections may require additional signal phases
and pedestrian signal heads to accommodate all movements safely.
3.Pedestrian and Bicycle Activity: The presence of pedestrians and cyclists affects signal design, with
dedicated pedestrian phases and bicycle signal heads often incorporated to ensure safe crossing and cycling
movements.
4.Safety Considerations: Signal design must prioritize safety for all road users, including motorists,
pedestrians, and cyclists. Factors such as sight lines, speed limits, and crash history inform signal placement
and timing adjustments to reduce the risk of accidents.
5.Vehicle Speed: The speed of vehicles approaching an intersection affects signal timing and placement.
Signals may be placed farther back from the intersection or utilize longer yellow phases to accommodate
higher speeds and provide adequate stopping distance.
6.Transit Priority: In areas with public transit, signal design may prioritize transit vehicles to improve
efficiency and reliability. Transit signal priority systems give buses priority at intersections, reducing delays
and improving service.
7.Emergency Vehicle Access: Signal design may incorporate features such as preemption systems to give
priority to emergency vehicles, ensuring rapid response times during emergencies.
8.Environmental Factors: Environmental considerations, such as weather conditions and visibility, influence
signal design. Signals may incorporate features such as backlit signal heads and snow shields to ensure
visibility in adverse conditions.
9.Traffic Patterns: Traffic patterns vary throughout the day, with peak hours requiring different signal timing
than off-peak hours. Signal design may include adaptive signal control systems that adjust timing based on
real-time traffic conditions to optimize flow.
10.Accessibility: Signal design must comply with accessibility standards to ensure all users, including those
with disabilities, can safely navigate intersections. This includes features such as audible pedestrian signals,
tactile indicators, and accessible pedestrian crossings.
By considering these factors, traffic engineers can design signals that effectively manage traffic flow, prioritize
safety, and accommodate the needs of all road users.
MERITS AND DEMERITS OF TRAFFIC SIGNALS
Traffic signals play a vital role in regulating traffic flow, enhancing safety, and improving efficiency on roads.
However, like any traffic control measure, they also have their merits and demerits:
Merits of Traffic Signals:
1.Safety Improvement: One of the primary advantages of traffic signals is their ability to improve safety by
regulating the flow of traffic at intersections. Clear signal indications help reduce the risk of collisions by
providing clear guidance to drivers, pedestrians, and cyclists.
2.Traffic Management: Traffic signals effectively manage the flow of vehicles at intersections, minimizing
congestion and delays. By assigning right-of-way to different movements, signals help distribute traffic
efficiently, especially during peak hours.
3.Pedestrian Safety: Pedestrian signals at intersections enhance safety by providing designated crossing times
and clearly indicating when it's safe to cross. This reduces conflicts between vehicles and pedestrians and
improves overall pedestrian safety.
4.Intersection Efficiency: Well-designed traffic signals can optimize the efficiency of intersections by
coordinating signal timing to reduce wait times and maximize throughput. This is particularly beneficial in
high-traffic areas and during peak travel times.
5.Transit Priority: Traffic signals can be programmed to give priority to public transit vehicles, improving the
efficiency and reliability of transit services. Transit signal priority systems reduce delays for buses and other
transit vehicles, encouraging the use of public transportation.
Demerits of Traffic Signals:
1.Congestion: While traffic signals can mitigate congestion to some extent, poorly designed or overly
restrictive signals can actually exacerbate traffic congestion by causing unnecessary delays and queuing,
especially during off-peak hours.
2.Delay: Traffic signals inherently introduce delays at intersections, as vehicles must stop and wait for their
turn to proceed. This delay can be frustrating for drivers, particularly when signals are not synchronized or
responsive to traffic conditions.
3.Environmental Impact: The stop-and-go nature of traffic signals can contribute to increased fuel
consumption and emissions, particularly in areas with frequent signal stops. This can have negative
environmental effects, including air pollution and greenhouse gas emissions.
4.Pedestrian and Cyclist Displacement: In some cases, traffic signals may prioritize vehicle movement at the
expense of pedestrians and cyclists, leading to longer wait times and reduced accessibility for non-motorized
road users.
5.Cost: Installing and maintaining traffic signal systems can be expensive, requiring investment in
infrastructure, equipment, and ongoing maintenance. Additionally, signal upgrades and modifications to
accommodate changing traffic patterns can incur additional costs.
Overall, while traffic signals offer significant benefits in terms of safety and traffic management, their
effectiveness depends on careful design, proper maintenance, and consideration of local traffic conditions and
user needs. Balancing the advantages and disadvantages of traffic signals is essential to optimizing their role
in transportation systems.
SIGNALIZED INTERSECTION
A signalized intersection is a type of intersection where traffic is controlled by traffic signals. These
intersections typically feature signal lights that regulate the flow of vehicles, pedestrians, and cyclists,
assigning right-of-way to different movements at specified times. Here are some key aspects of signalized
intersections:
Operation:
1.Traffic Lights: Signalized intersections typically have multiple traffic lights, each with red, yellow, and
green indications. These lights control the movement of vehicles in different directions.
2.Phases: Signalized intersections operate in phases, with each phase allowing specific movements to proceed
while restricting others. Phases may include green lights for through traffic, left turns, right turns, and
pedestrian crossings.
3.Timing: Signal timing determines the duration of each phase and the sequence in which they occur. Timing
plans are designed based on factors such as traffic volume, pedestrian activity, and intersection geometry.
Components:
1.Signal Heads: These are the physical units containing the traffic lights. Signal heads are typically mounted
on poles or overhead structures and positioned to be visible to drivers, pedestrians, and cyclists.
2.Pedestrian Signals: Signalized intersections often include pedestrian signal heads with "walk" and "don't
walk" indications, allowing pedestrians to safely cross the intersection.
3.Detection Systems: Many signalized intersections use detection systems, such as loop detectors or cameras,
to detect the presence of vehicles and adjust signal timing accordingly. This helps optimize traffic flow and
reduce wait times.
Advantages:
1.Safety: Signalized intersections enhance safety by reducing the risk of collisions through controlled
movements and clear right-of-way assignments.
2.Traffic Management: By regulating the flow of vehicles, signalized intersections help manage traffic
congestion and improve overall traffic efficiency.
3.Pedestrian Safety: Pedestrian signals at signalized intersections provide designated crossing times and help
ensure safe interactions between pedestrians and vehicles.
Challenges:
1.Congestion: Signalized intersections can contribute to congestion, particularly during peak traffic periods,
if signal timing is not optimized or if traffic volumes exceed the intersection capacity.
2.Delay: Stop-and-go traffic at signalized intersections can lead to delays for motorists, cyclists, and
pedestrians, especially if signal timing is not synchronized or if there are frequent stops.
3.Maintenance: Signalized intersections require regular maintenance to ensure that traffic lights, detection
systems, and other components are functioning properly. Malfunctions or failures can disrupt traffic flow and
compromise safety.
Overall, signalized intersections are a common and effective method of traffic control, providing safe and
efficient movement of vehicles, pedestrians, and cyclists at intersections. Proper design, operation, and
maintenance are essential to maximizing their benefits and addressing challenges.
SIGNAL COORDINATION
Signal coordination, also known as traffic signal synchronization, is a technique used to optimize traffic flow
and reduce delays along a corridor or network of interconnected intersections. Here's how signal coordination
works and its benefits:
How Signal Coordination Works:
1.Timing Plans: Traffic engineers develop timing plans for each intersection within a coordinated corridor.
These plans specify the duration of each signal phase (e.g., green, yellow, red) and the sequence in which
phases occur.
2.Offset Timing: Signal timing is adjusted to create offsets between adjacent intersections, ensuring that traffic
progression is smooth and vehicles encounter fewer stops along the corridor.
3.Cycle Length: The total duration of signal phases, known as the cycle length, is optimized to accommodate
traffic demand and minimize delays. Longer cycle lengths are typically used for intersections with higher
traffic volumes.
4.Adaptive Control: Some signal coordination systems utilize adaptive control algorithms that continuously
monitor traffic conditions and adjust signal timing in real time to optimize traffic flow based on current
demand.
Benefits of Signal Coordination:
1.Reduced Delay: By coordinating signals to create green waves, signal coordination minimizes the number
of stops and delays experienced by motorists along a corridor, leading to shorter travel times and improved
mobility.
2.Improved Traffic Flow: Coordinated signals help maintain consistent traffic speeds and reduce the
likelihood of congestion by facilitating the smooth progression of vehicles through consecutive intersections.
3.Fuel Savings and Emissions Reduction: Reduced delays and smoother traffic flow resulting from signal
coordination lead to lower fuel consumption and emissions, contributing to environmental sustainability and
air quality improvement.
4.Enhanced Safety: Signal coordination can improve intersection safety by reducing the likelihood of rear-
end collisions and aggressive driving behaviors associated with frequent stops and delays.
5.Transit Priority: Coordinated signal systems can be designed to prioritize public transit vehicles, such as
buses, by minimizing their travel times and improving schedule adherence, thus encouraging the use of
sustainable transportation modes.
Challenges and Considerations:
1.Complexity: Coordinating signals across multiple intersections requires careful planning and coordination
among traffic engineers, considering factors such as traffic volumes, intersection geometries, and pedestrian
needs.
2.Balancing Priorities: Signal coordination must strike a balance between optimizing traffic flow for motorists
and accommodating the needs of pedestrians, cyclists, and transit users to ensure equitable access and safety
for all road users.
3.Adaptability: Signal coordination systems should be adaptable to changing traffic conditions, such as
fluctuations in demand due to events, construction, or special circumstances, to maintain optimal performance
over time.
Overall, signal coordination is a valuable tool for improving traffic efficiency, reducing delays, and enhancing
safety along urban corridors, contributing to a more sustainable and livable transportation environment.
DELINEATORS
Delineators are traffic control devices used to guide and warn motorists by visually delineating the edges of
roadways, lanes, and other areas. They typically consist of reflective markers or posts mounted on the roadway
or its periphery. Here's more about delineators:
Types of Delineators:
1.Tubular Delineators: These are cylindrical tubes, often made of plastic or metal, with reflective surfaces.
They are commonly used to mark the edges of roadways, lanes, curves, and medians. Tubular delineators are
flexible and can withstand vehicle impacts without causing significant damage.
2.Flexible Delineators: Similar to tubular delineators, flexible delineators are made of resilient materials such
as rubber or plastic. They are designed to bend or flex upon impact, reducing the risk of vehicle damage and
injury. Flexible delineators are often used in locations where there is a higher likelihood of vehicle
encroachment, such as narrow lanes or work zones.
3.Reflective Panels: These are flat panels or sheets with reflective surfaces, often mounted vertically on posts.
Reflective panels are used to delineate lanes, medians, and other areas where additional visibility is needed,
particularly at night or in low-light conditions.
4.Raised Pavement Markers (RPMs): While not always considered delineators in the traditional sense, raised
pavement markers are small reflective devices embedded in the roadway surface. They provide tactile and
visual guidance to drivers, particularly in adverse weather conditions or when visibility is limited.
Purpose and Benefits:
1.Visibility Enhancement: Delineators improve the visibility of roadway edges, lane markings, and other
critical features, especially during nighttime or inclement weather conditions. The reflective materials used in
delineators increase their visibility to motorists.
2.Lane Definition: Delineators help define lane boundaries and guide drivers, reducing the likelihood of lane
departure accidents and improving overall roadway safety.
3.Warning of Hazards: Delineators are often used to warn drivers of hazards such as curves, obstructions, or
changes in roadway alignment. They provide a visual cue to motorists, alerting them to potential dangers
ahead.
4.Traffic Channelization: Delineators assist in channelizing traffic by directing vehicles along desired paths,
particularly in temporary or construction zones where lane shifts or closures are in effect.
5.Flexibility and Durability: Many delineators are designed to withstand vehicle impacts and harsh
environmental conditions. Their flexibility and resilience make them suitable for use in various roadway
settings.
Considerations:
1.Proper Placement: Delineators should be installed according to established guidelines and standards to
ensure effectiveness and avoid confusion among motorists.
2.Maintenance: Regular inspection and maintenance are essential to ensure that delineators remain intact,
visible, and properly aligned. Damaged or missing delineators should be promptly replaced to maintain
roadway safety.
3.Compatibility with Road Users: Delineators should be designed and placed in a manner that minimizes
interference with pedestrians, cyclists, and other road users while still providing effective guidance to
motorists.
Overall, delineators are valuable tools for improving roadway safety, enhancing visibility, and guiding
motorists in various traffic and roadway conditions. Proper selection, placement, and maintenance are critical
to their effectiveness in promoting safe and efficient travel.
ATTENUATORS
Attenuators are safety devices installed on roads and highways to absorb or redirect the kinetic energy of a
vehicle during a collision, thereby reducing the severity of the impact and minimizing the risk of injuries to
vehicle occupants and damage to infrastructure. Here's more about attenuators:
Types of Attenuators:
1.Crash Cushions: Crash cushions are designed to absorb the kinetic energy of a vehicle by deforming upon
impact. They are typically made of materials such as foam, plastic, or metal, and are installed at the ends of
concrete barriers, bridge piers, and other fixed structures to protect motorists from abrupt stops.
2.Trailing-End Attenuators: Trailing-end attenuators are mounted at the rear of stationary objects, such as
concrete barriers or guardrails, to absorb the energy of a vehicle that may strike them from behind. They are
designed to collapse or deform progressively upon impact, reducing the severity of the collision.
3.Truck-Mounted Attenuators (TMAs): TMAs are safety devices attached to the rear of trucks or other
vehicles to protect highway workers and motorists in mobile work zones. They consist of a series of collapsible
elements designed to absorb the impact of a vehicle and provide a cushioned barrier.
4.Water-Filled Barriers: Water-filled barriers are temporary attenuators used in construction zones, events, or
other locations where traffic patterns may need to be temporarily altered. These barriers are filled with water
to provide stability and absorb energy upon impact.
Purpose and Benefits:
1.Collision Mitigation: The primary purpose of attenuators is to mitigate the severity of collisions by absorbing
or redirecting the energy of a vehicle upon impact. This helps protect motorists, passengers, and workers from
injury and reduces damage to vehicles and infrastructure.
2.Work Zone Safety: Attenuators play a crucial role in enhancing safety in work zones by providing a
protective barrier between moving traffic and construction activities. They help reduce the risk of accidents
and injuries to workers and motorists in temporary construction zones.
3.Infrastructure Protection: Attenuators help protect fixed objects, such as bridge piers, concrete barriers, and
guardrails, from damage caused by vehicle collisions. By absorbing the energy of a vehicle, attenuators help
minimize the impact on infrastructure and reduce the need for costly repairs.
4.Traffic Management: Attenuators can also be used to manage traffic flow and control access to certain areas,
such as construction zones or temporary events. By providing a visible barrier to drivers, attenuators help
guide traffic safely through potentially hazardous areas.
Considerations:
1.Installation and Maintenance: Proper installation and regular maintenance are essential to ensure that
attenuators function effectively when needed. Inspections should be conducted regularly to identify and
address any signs of wear, damage, or deterioration.
2.Compatibility: Attenuators should be selected and installed based on the specific requirements of the
roadway or work zone, taking into account factors such as vehicle speeds, traffic volumes, and the presence
of fixed objects.
3.Visibility and Signage: Attenuators should be clearly marked and accompanied by appropriate signage to
alert motorists to their presence and indicate changes in traffic patterns or conditions.
Overall, attenuators are critical safety devices that help protect motorists, passengers, workers, and
infrastructure from the potentially devastating effects of vehicle collisions. Proper selection, installation, and
maintenance are essential to maximizing their effectiveness in enhancing roadway safety.
TRAFFIC SAFETY BARRIERS
Traffic safety barriers are structures designed to enhance safety on roads and highways by providing physical
separation between vehicles, preventing cross-median collisions, and reducing the severity of accidents. They
come in various types and are strategically placed to mitigate the risks associated with different roadway
configurations and traffic conditions. Here are some common types of traffic safety barriers:
1. Concrete Barriers:
New Jersey Barrier: Also known as "Jersey barriers," these are low-profile concrete barriers with a distinctive
angled shape. They are commonly used for dividing opposing traffic lanes and protecting against head-on
collisions.
F-Shape Barrier: Similar to New Jersey barriers, F-shape barriers have an extended vertical face at the bottom,
providing additional stability and impact resistance.
2. Steel Barriers:
Guardrails: Steel guardrails are long metal barriers installed along the edges of roads to prevent vehicles from
leaving the roadway or colliding with roadside obstacles. They are often used on curves, bridges, and steep
embankments.
W-Beam Barrier: W-beam barriers consist of horizontal beams supported by vertical posts. They are flexible
and designed to absorb and dissipate the energy of a vehicle upon impact.
3. Cable Barriers:
Cable Median Barrier: Cable barriers are composed of steel cables strung between posts to create a flexible
barrier in the median of a divided highway. They are effective at preventing crossover collisions while
minimizing the risk of vehicle rollovers.
Cable Guardrail: Similar to cable median barriers, cable guardrails are installed along the edge of the roadway
to redirect vehicles and prevent them from leaving the road.
4. Water-Filled Barriers:
Plastic Water-Filled Barriers: These temporary barriers are made of plastic and filled with water to provide
stability. They are commonly used in construction zones, work areas, and events to redirect traffic and provide
a physical barrier between vehicles and workers.
5. Bollards:
Steel Bollards: Bollards are short, sturdy posts typically made of steel or concrete. They are often used to
protect pedestrians, buildings, and infrastructure from vehicle collisions in urban areas, parking lots, and
pedestrian zones.
Benefits of Traffic Safety Barriers:
1.Collision Mitigation: Barriers help reduce the severity of accidents by absorbing impact energy and
preventing vehicles from colliding with obstacles, oncoming traffic, or leaving the roadway.
2.Roadway Separation: Barriers provide physical separation between opposing lanes of traffic, reducing the
risk of head-on collisions and crossover accidents.
3.Enhanced Safety: By reducing the likelihood of accidents and injuries, traffic safety barriers improve overall
roadway safety for motorists, passengers, pedestrians, and cyclists.
4.Traffic Control: Barriers can be used to manage traffic flow, guide vehicles through construction zones, and
protect workers and equipment in work areas.
Considerations for Deployment:
1.Proper Installation: Traffic safety barriers should be installed according to established standards and
guidelines to ensure effectiveness and durability.
2.Maintenance: Regular inspection and maintenance are essential to ensure that barriers remain intact, visible,
and capable of performing their intended function.
3.Visibility: Barriers should be highly visible to motorists, particularly in low-light conditions or adverse
weather, to effectively communicate roadway hazards and changes in traffic patterns. Reflective materials and
signage can enhance visibility.
4.Adaptability: Barriers should be selected and deployed based on the specific needs and conditions of the
roadway, considering factors such as traffic volume, vehicle speeds, and geometric constraints.
