Click for next page ( 8


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 7
CHAPTER 3 Design Controls As with other types of roadway geometric features, the test of how well or how poorly a drive- way connection is designed is determined by how well or how poorly the connection operates after it is opened. To anticipate the consequences of a design choice before a facility is actually constructed and opened for use, the designer needs to identify the setting and understand the performance characteristics and limitations of the users--bicyclists, drivers, pedestrians, and motor vehicles. Although there will always be exceptions, the following material describes generally prevalent situations in the United States. These considerations are incorporated into the more detailed design guidelines presented in Chapters 4 and 5. The Driveway Setting The design of a driveway is affected by its setting and land use. The environment can be urban, suburban, or rural. The various characteristics of a driveway serving a tract with commercial land use are quite different from a driveway serving a single-family residence. Combinations of these characteristics and other factors affect the final design choices. The differences between urban, suburban, and rural settings can be characterized by develop- ment density, the spacing of parallel and intersecting streets, levels of bicycle and pedestrian traf- fic, and the availability of public transit service. In contrast to rural areas, built-up urban areas typically have lower speeds, more frequent intersections, many more pedestrians, and often bus service. In urban settings, especially in central business districts (CBDs), driveway geometry can be more constrained than in suburban and in rural areas. Exhibit 3-1 lists the relative impor- tance of travel modes, based on the location and development density of the activities to be served. The relative importance can help the designer determine how to address the sometimes conflicting needs of different modes. Although all types of property tracts need access to and from public roadways, the nature of that need varies according to the type of land use (e.g., agricultural, commercial, and residential). The type of land use is typically associated with factors such as the volume of traffic and the types of vehicles in and out of the driveway. Exhibit 3-2 lists common types of driveways, illustrative appli- cations, and some considerations affecting the design. The organization reflects combinations of factors that designers commonly encounter. "Standard" driveways are grouped by intensity of use--very high, higher, medium, and lower. "Special situation" driveways include those that cre- ate special needs (e.g., a driveway in a city center or serving a farm or ranch, a field, or an industry). Exhibit 3-2 does not list all of the possible combinations of land use and surrounding envi- ronment; a list of all combinations would be extremely complex and unwieldy. The designer 7