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8 Guide for the Geometric Design of Driveways Exhibit 3-1. Driveway settings and the importance of various modes. Area Type Descriptive Attributes Relative Importance of Mode (as determined by the actual choices the public is observed to make) Auto Bicycle Ped Transit Urban Core Connected buildings Medium Medium High High to (CBD and other Sidewalk paved from curb edge to the Medium major urban face of buildings centers) Shorter blocks Higher pedestrian volumes In some locales, higher volumes of transit vehicles and riders Motor vehicle traffic is often congested and moving relatively slowly General Urban May include special districts (e.g., High Medium Medium Medium outlying business districts that are not in an urban core) Bicycles and pedestrians are present In some locales, public transit vehicles and riders are present Suburban Motor vehicles are predominate mode High Low Low Low A few bicycles and pedestrians are present In some locales, occasional public transit is present Exurban Motor vehicles are predominate mode High Low Low Low Bicycles, pedestrians, and/or transit are infrequent Rural (farm or Motor vehicles are predominate mode High Very Very Very ranch) Higher speeds need longer access low low low spacing NOTES: "Ped" = Pedestrian "Relative Importance" is affected by region. For instance, public transit is more prevalent in some regions than in others. must exercise good judgment that reflects an understanding of traffic characteristics when cat- egorizing a particular driveway and applying design standards. For instance, the small radius and steep grades that some agencies allow for residential driveways will probably be unsuit- able for a single-family residential driveway connecting to a busy thoroughfare. Land use type alone is not a sufficient criterion for design; the designer must consider other factors, includ- ing the site environment. User Mix Considerations Bicyclists, motorized-vehicles (e.g., automobiles, buses), pedestrians, pedestrians with disabil- ities (e.g., persons using mobility aids such as wheelchairs, or pedestrians with visual impair- ments) all occupy and use transportation facilities in the United States. In the area where the roadway, the sidewalk, and the driveway intersect, there are three distinct user groups with dif- ferent and sometimes conflicting needs (see Exhibit 3-3). Although members of each group typ- ically want to make their trips as expeditiously as possible, the roadway user is usually moving at a greater speed and therefore is often focused on the roadway some distance ahead. The sidewalk users (e.g., pedestrians, pedestrians with mobility disabilities) are moving at a much slower pace, and are unprotected and vulnerable to vehicles. The area may be used by those waiting for a bus or taxi. The driveway user typically has a speed and a path that can create conflicts with the other two user groups.
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Design Controls 9 Exhibit 3-2. Driveway categories. Category Description of Common Applications* Considerations Affecting Design STANDARD DRIVEWAYS Very high Urban activity center, with almost constant driveway use Very high site volume. These sites are intensity during hours of operation. Typified by a driveway often on streets with relatively high serving a post-1950 major shopping center or office speeds and volumes. For these complex. These driveways often look like public driveways, refer to street design roadways. Not uncommon for these driveways to be guides. signalized. Higher Medium-size office or retail, such as community These sites are often on streets with intensity shopping center, with frequent driveway use during relatively high speeds and volumes. hours of operation. Also includes land uses with Expect more than one exiting vehicle extreme peaking patterns, such as public schools, at a time. worship assemblies, and employee parking lots. Medium Smaller office or retail, such as convenience stores, with These sites may be on streets with intensity occasional driveway use during hours of operation. Also relatively high speeds and volumes. includes some apartment complexes. Seldom more than one exiting vehicle at a time. Lower Typical applications include single-family or duplex If on a lower-speed, lower-volume intensity residential, or other types with low use. May not apply roadway, conflicts with other to rural residential. vehicles are relatively less frequent. The driveway is used by only one vehicle at a time. SPECIAL SITUATION DRIVEWAYS Central Building faces are close to the street. May have on- Vehicles entering a driveway may business street parking or bus stops, a continuous sidewalk from encounter a higher frequency of district the curb to faces of buildings, and higher pedestrian conflict with other users, such as usage than in most other environments. Many situations pedestrians. Through motorists expect will serve P-vehicles and some single-unit trucks. more frequent traffic interruptions. Farm or May be a mixture of residential and industrial May be on a highway with a posted ranch characteristics, used by a mix of design vehicles, such as speed of 50 mph or more. P-vehicle, single-unit truck, and agricultural equipment. Pedestrian use is extremely rare. The driveway is used by only one vehicle at a time. Field Serves a field or other similar land area that is seldom Many days may elapse between uses. (Very low trafficked. Higher-clearance P-vehicles or heavy Pedestrian use is extremely rare. intensity) vehicles are expected. The driveway is used by only one vehicle at a time. Industrial Driveways frequently used by buses, tractors with semi- The extra axles and longer wheelbase trailers, and other vehicles longer and wider than the will lead to much greater offtracking design P-vehicle. of vehicles entering the driveway. Other Identify the specific vehicles that will use the facility. Bus terminal Consider the width, Example bus terminal and swept path of turning buses and circulation patterns. Example emergency vehicles Emergency vehicles Need to exit heading out, not backing. May need on-site turn around. NOTE: P-vehicle is a passenger car design vehicle, which includes minivans and pickup trucks. * These descriptions are intended to help the designer form a mental image of some of the more common examples of the category. These interactions take place within or near the border, the area between the Exhibit 3-3. Users in the driveway, roadway edge and the right-of-way line. Objects in the border can affect the roadway, sidewalk area. users. For instance, a poorly placed roadside bus shelter can be an impediment in the path of a pedestrian with a visual impairment and may make it more dif- Driveway users ficult for a motorist exiting the driveway to see oncoming traffic. Driveway design practice should address many issues. Some broad consider- border area Sidewalk users ations include the following: border area · Convenient and safe vehicle egress and ingress; · Sight distance and safety for sidewalk users; Roadway users