Questions and Answers
What is the most important rule in highway design?
Which organization governs the operation and standards related to highway engineering?
Which term refers to a public road built with ditches on both sides and elevated in the middle?
What is a key aspect of roadway facilities being considered satisfactory?
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What does a divided arterial highway generally provide at major intersections?
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What is the average daily traffic (ADT) range for a Collector Level road to reach a level of service of 90?
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Which of the following factors does NOT play a role in determining the cross section of a typical highway?
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Based on the statistics provided, what is the percentage decrease in accidents for a 7.2 meters wide pavement compared to one narrower than 5.50 m?
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What is the original width of the road before the adjustment mentioned?
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Which shoulder width configuration recorded a 30% decrease in accidents when comparing 6.00 m and 7.20 m wide pavements?
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Study Notes
Designing the Highway
- Consistency is essential in highway design to provide clear guidance through road signs and avoid abrupt changes in traffic and road standards.
- Highways are designed for various vehicles operated by drivers who depend on clear information and smooth transitions.
- Proper integration of highway signs and directions is critical during preliminary layout studies for effective communication.
Definition of Key Terms
- AASHTO: American Association of State Highway and Transportation Officials; responsible for governing operations and setting specifications and standards for highway engineering.
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Roads and Highways:
- Roads: Public thoroughfare, which may also refer to railways.
- Highway: Public road typically built on elevated land with ditches on either side for drainage.
Average Daily Traffic (ADT) Classifications
- Classifications for rural collectors and local roads based on ADT across different terrains:
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Collector Roadways:
- Level: 60 to 90 vehicles
- Rolling: 45 to 75 vehicles
- Mountainous: 30 to 60 vehicles
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Local Roadways:
- Level: 45 to 75 vehicles
- Rolling: 30 to 60 vehicles
- Mountainous: 30 to 45 vehicles
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Collector Roadways:
Cross Section of Typical Highway
- Evaluation of variables in cross section design includes traffic volume, character, speed, and vehicle/driving characteristics.
- High volume traffic roads usually maintain uniform thickness across the cross-section; lower volume roads may vary shoulder widths to reduce costs.
- Accident statistics indicate wider pavements (7.2m) show significantly reduced accidents compared to narrower pavements.
Standard Widths
- Typical adjustments for roadway width:
- Original: 4.5m; adjusted to 4.8m-5.4m.
- Freeways: 3.60m; two-lane rural highways require 7.20m for safety.
- Local rural roadways: 4.80m for a design speed of 30 km/h; urban roadways: 3.80m or 3.00m if space is constrained.
Importance of Road Shoulders
- Road shoulders provide stopping space for disabled vehicles, enhance safety, and should be continuous for effective roadway structure.
- Policy recommendations include:
- Outside shoulder widths of at least 3.00m to 3.60m for trucks.
- Median shoulder widths from 1.20m to 3.60m, depending on traffic volume.
- Shoulders enhance sight distance at curves and serve as guidance in poor visibility conditions.
Cross, Cut, and Fill Slope
- Cross Slope: Typically falls away from the centerline at 1%-2%, ensuring water drainage.
- Cut/Fill Slope: Normal earth fill should adhere to ratios of 1:2; rock cuts can be as steep as 1:4.
- Recommended design ratios vary for embankments and cut slopes to ensure stability and safety for vehicles.
Highway Median and Grade Line
- Highway Median: Offers refuge from opposing traffic, reduces glare, and aids in left turns. Recommended widths vary depending on traffic conditions.
- Measures to mitigate cross median accidents include barriers and deterring devices.
- Grade Line: Represents the longitudinal profile of the highway, focusing on minimizing earthwork and ensuring proper drainage.
Economic Considerations
- In mountainous areas, earthwork balance is essential to minimize costs.
- In flat areas, the grade line should ensure adequate drainage while being economically feasible.
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Description
Dive into the fundamental concepts of highway design in this module. This quiz covers the critical elements from Chapter Two, focusing on consistency and other essential design principles. Perfect for students looking to enhance their understanding of highway engineering.
