Geometric Design: General Concept CE331 Transportation Engineering

Objectives Maximize Comfort Safety Economy Minimize Environmental impacts … Design a safe and efficient system that addresses community and environmental needs

Highway Classification Location Rural Urban Functional class Arterial (Principal and Minor Collector (Major and Minor) Local Designation Interstate Federal State County Local

Functional Class - example Prin. Arterial Minor Arterial Collector

Some Characteristics Major Arterial Minor Arterial Collectors Local roads Veh-miles Lane-miles Mobility Accessibility Think of it like this: as you move from local roads upwards in functional classification towards major arterials, what happens to each of these 4 measures? Answer: vehicle miles and mobility go up. Lane miles and accessibility go down.

Mobility vs. Accessibility Arterial Collectors Locals Mobility Land Access

What?

What Affects Highway Design? Human, vehicle characteristics Expected volume and its composition Topography of the area Functional classification Level-of-service to be provided Land use and environmental factors Community concerns Funding

Basic Terms Design Hourly Volume (DHV) Expected number of vehicles in one hour in both directions Directional Design Hourly Volume (DDHV) Expected number of vehicles in one hour in one direction Average Daily Traffic (ADT) Number of vehicles in 24 hours in both directions Average Annual Daily Traffic (AADT) Number of vehicles in 24 hours in both directions

Basic Terms (cont’d) Design Speed Choice speed to design for while balancing safety, mobility, community issues, and environmental concerns Operating Speed Average speed people drive with comfort Speed limit Maximum legal speed

Basic Terms (cont’d) Design Vehicle Group of vehicles selected for establishing design control on highways with typical physical and operational characteristics General classes: Passenger car Bus Truck Recreational vehicle

Design Vehicles Which one? Largest with reasonable frequency?

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Roadway Cross Section Shoulder Traveled way Roadway Clear Zone Right of Way Median

Cross Section Components

Travel Lanes Purpose Width feet Arterials and freeway 12 feet Cross slope 1-2% Always?

Shoulders Purpose Refuge area Recovery area Pavement support Width 2-12 feet Slope 2-4%

Median Purpose Divide traffic Recovery area Storage area Refuge area Aesthetics Width Varied Types Raised Flush Depressed

Right-Of-Way Total land required for the construction of the highway Needs to be wide enough to accommodate all the elements of highway cross section and planned widening of the highway, and all public utility facilities to be installed along the highway Example: 2-lane urban collector streets: 40-60ft 2-lane urban arterials: 84ft

Highway Alignment Not all roads are straight and level Vertical components Grades Curves Horizontal components Tangents Curves