Roadway Horizontal Alignments

In Roadway Horizontal Alignments, you'll learn ...

• What is side friction factor and how to calculate it
• Methods for attaining superelevation in a spiral curve
• Cases where speed, curvature, or width may require appropriate traveled way widening
• How intersection sight distance varies according to the different types of traffic control
• Procedure for coordination of horizontal and vertical alignments

Overview

Preview a portion of this course before purchasing it.

Credit: 3 PDH

Length: 51 pages

The roadway horizontal alignment is a series of horizontal tangents (straight roadway sections), circular curves, and spiral transitions. It shows the proposed roadway location in relation to the existing terrain and adjacent land conditions. Together with the vertical alignment (grades and vertical curves) and roadway cross-sections (lanes, shoulders, curbs, medians, roadside slopes, ditches, sidewalks), the horizontal alignment (tangents and curves) helps to provide a three-dimensional roadway layout.

In today’s environment, designers must do more than merely apply design standards and criteria to ‘solve’ a problem. They must understand how various roadway elements contribute to safety and facility operation, including the horizontal alignment.

This course focuses on the geometric design of horizontal alignments for modern roads and highways. Its contents are intended to serve as guidance and not as an absolute standard or rule. Upon course completion, you should be familiar with the general design of horizontal roadway alignments. The course objective is to give engineers and designers an in-depth look at the principles to be considered when designing horizontal alignments.

Specific Knowledge or Skill Obtained

This course teaches the following specific knowledge and skills:

• What is horizontal alignment
• Why design speed selection is a critical decision that should be done at the beginning of the planning and design process
• Maximum superelevation rates and minimum curvature
• How grades affect superelevation rates
• Locations where "tangent-to-curve" transitions are used
• The AASHTO equation for determining the minimum length of superelevation runoff
• How to locate a curve's superelevation runoff with respect to its Point of Curvature (PC)
• When to use spiral curves
• The AASHTO formula for the minimum length of a spiral curve
• Maximum spiral radius
• Minimum and maximum spiral length
• Length of tangent runoff and superelevation runoff in a spiral curve
• Axis of rotation when a median is present
• Two types of drainage problems for pavement surfaces in superelevation transition sections
• Factors that impact the amount of widening on horizontal curves needed for offtracking
• Determination of stopping sight distance (SSD) and decision sight distance (DSD)
• Design values for passing sight distance on two-lane highways
• General controls for horizontal alignments

Certificate of Completion

You will be able to immediately print a certificate of completion after passing a multiple-choice quiz consisting of 25 questions. PDH credits are not awarded until the course is completed and quiz is passed.