Geometric Alterations and Considerations

General Description:

Geometric Alterations have an impact on traffic volumes, speeds, and sight distances.  Changing the geometry of the roadway can positively affect traffic characteristics based on the desired effect.  There are four types of geometric design elements that can be manipulated. 

Category Design Element

Horizontal Alignment                         Degree of Curvature, Super elevation

Vertical Alignment                             Grade, Vertical Curves

Cross Section                                   Lanes, Lane Widths, Shoulders, Medians

Roadside                                           Slopes, Ditches, Barriers

The desired effect must be determined before any geometric changes should be considered.

Effects of Solution:

¨ Increase Passenger Throughput

þ Increase Roadway Capacity (Subtle changes can impact the capacity)

¨ Manage System Efficiency

¨ Reduce Local Demand

Geometric changes can increase roadway capacity with additional lanes or higher speeds.  Some changes (i.e. Traffic Calming) can reduce the demand on a facility.

Examples of Implementation:

No specific examples available at the time of publication.

Cost/Financial Information:

Please refer to the Traffic Calming fact sheet for specific cost information.

Additional Resources:

A Toolbox for Alleviating Traffic Congestion and Enhancing Mobility, available for order at http://www.ite.org/bookstore/index.asp

Traffic Calming Toolbox, available at http://www.ite.org/traffic/index.html

Transportation Research Record 1751: Geometric Design and the Effects on Traffic Operations 2001

Transportation Research Board Special Report 254: Managing Speed

http://gulliver.trb.org/publications/sr/sr254.pdf#search='trb%20sr%20254'

Federal Highway Administration publication: Flexibility in Highway Design

http://www.fhwa.dot.gov/environment/flexibility/index.cfm

National Park Service: Links to Roads and Parkways Information:

http://www.nps.gov/transportation/roads/links.htm

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