Essential Concepts in Roadway Design and Traffic Engineering

Roadway Components Defined

• A – Road reserve
• B – Roadbed
• C – Verge
• D – Median
• E – Median island

Pavement Layers: Top to Bottom

The 5 layers of a typical pavement, in correct sequence from top to bottom, are:

1. Surfacing
2. Base
3. Subbase
4. Selected layers
5. Subgrade

Objectives of Traffic Calming

Five key objectives of traffic calming include:

• Reduce speed
• Reduce traffic volumes
• Reduce noise pollution
• Reduce air pollution
• Provide safety to non-motorized areas

Importance of Minimum Turning Radius

The reason for needing a minimum turning radius in road design is to ensure that vehicles can navigate corners safely and efficiently.

Defining Operating Speed

Operating speed is defined as the highest speed under prevailing conditions.

Types of Sight Distances in Road Design

The types of sight distances that should be considered in road design include:

• Stopping Sight Distance (SSD)
• Barrier Sight Distance (BSD)
• Decision Sight Distance (DSD)
• Passing Sight Distance (PSD)
• Intersection Sight Distance (ISD)
• Pedestrian Sight Distance (PSD)

Necessity of Design Vehicles in Geometric Design

Two reasons why a design vehicle is necessary in geometric design are:

• To provide a model for planning and design.
• To facilitate the use of templates for design.

Traffic Calming for Residential Streets

Scenario: A residential street is 1500m long with a design speed of 60km/h. There is no intersection or traffic calming along this street.

Recommendation: Yes, an intersection or traffic calming measures would be recommended.

Reasoning: For a design speed of 60 km/h, a typical maximum segment length without intersections or calming is around 600m (60 km/h * 10m/km/h). Since 600m is less than the street's length of 1500m, adding an intersection or traffic calming elements is advisable to manage speed and improve safety along the extended segment.

Key Attributes of Design Vehicles

Reasons why a design vehicle is required in street design are:

• It serves as a design model that considers all relevant factors of a vehicle when designing a road.
• Design vehicles are self-propelled, occupy space, and have a measurable speed of movement.

Essential Road Surface Qualities

Three important road surface qualities to evaluate during road design are:

• Skid resistance
• Riding quality
• Noise

Factors for Adding Climbing Lanes on Rural Roads

Two factors that need to be evaluated when deciding whether or not to add climbing lanes on a rural road are:

• The percentage of trucks or slow-moving vehicles traveling on that road.
• The gradient and curvature of the rural road.

Measures of Effectiveness in Roadway Systems

Measures of effectiveness typically:

• Measure the level of use or utility.
• Manage the operation or provision of infrastructure.
• Enhance productivity.
• Ensure enough capacity of the road.
• Utilize the Highway Capacity Manual (HCM), which includes:
  • Level of Service (LOS)

Fundamental Road Design Parameters

Basic design parameters include:

• The design vehicle
• The design driver
• The road surface

Core Elements of Road Design

Key elements of road design are:

• Design speed
• Design hour
• Ceiling speed

Key Elements of Cross-Section Design

Elements of cross-section design include:

• Lanes
• Shoulders
• Medians and outer separators
• Verges
• Sidewalks
• Slopes

Intersection Efficiency Metrics

Measures of efficiency at intersections include:

• Energy consumption
• Time delays
• Safety
• Convenience

Methods of Intersection Control

Types of intersection control are:

• Signalization
• Multi-way stop or yield
• Mini roundabouts, traffic circles, and gyratories
• Priority controls

Common Forms of Intersections

Common forms of intersections include:

• Three-leg intersection
• Four-leg intersection
• Multi-leg intersection

Various Types of Road Lanes

Types of road lanes include:

• Basic or through lanes
• High-occupancy lanes
• Auxiliary lanes
• Parking lanes
• Cycle lanes

Key Functions of Road Pavements

Four essential functions of a pavement are:

• Provide a smooth riding surface
• Provide adequate surface friction
• Protect the subgrade
• Provide waterproofing