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CHAPTER 2 Terms and Definitions This chapter presents terms and definitions used in this report. Exhibit 2-1 illustrates the loca- tion of some of the named driveway design elements. AASHO ­ American Association of State Highway Officials AASHTO ­ American Association of State Highway and Transportation Officials ADA ­ Americans with Disabilities Act of 1990 Blended transition ­ A connection with a grade of 5% or less between the level of the pedestrian walkway and the level of the crosswalk (2-1). Breakover angle ­ The algebraic difference between two successive grades. CBD ­ Central business district: the established "downtown" core or center of a city that tradi- tionally included government, office, and retail activities. Commercial driveway ­ Driveways that serve uses such as offices, retail, or services. Connection ­ The junction of the subject roadway with a source of traffic from the side (e.g., a driveway, roadway, or ramp). Contrast ­ A marked difference between dark and light. With regard to ADA contrast for detectable warnings, the ADA Standards state the following in the advisory appendix section. A4.29.2 Detectable Warnings on Walking Surfaces. The material used to provide contrast should contrast by at least 70%. Contrast in percent is determined by: contrast = [(B1 ­ B2)/B1] × 100 where B1 = light reflectance value (LRV) of the lighter area and B2 = light reflectance value (LRV) of the darker area. Note that in any application both white and black are never absolute; thus, B1 never equals 100 and B2 is always greater than 0. Cross slope ­ The slope (or grade) perpendicular to the direction of travel. On a sidewalk or blended transition, it is measured perpendicular to the curb line or roadway edge. On a curb ramp, it is measured perpendicular to the longitudinal or running grade. Driveway triangular island ("pork chop") ­ Roadway or driveway channelization in the form of a somewhat-triangular island. Dust pan ­A driveway entry or exit shape with the plan view designed with a flared or tapered edge. With this design, the curb height along the roadway edge transitions from full height to no curb height. Thus, the design incorporates a taper in both the plan and in the front elevation views. Front overhang ­ The distance from the center of the front-most wheel to the front end of the vehicle. Functional area of intersection ­ The area that includes not only the physical area where roadways cross each other, but also the areas upstream and downstream of the physical intersection, where driver reaction, deceleration, queuing, and acceleration occur that are related to the operation of the intersection. Ground clearance ­ The distance from the bottom of a vehicle body to the ground. 4

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Terms and Definitions 5 Exhibit 2-1. Some driveway design elements. Hang-up ­ When the underside of a vehicle comes into contact with the roadway surface, at grade breaks in the vertical profile, such that the vehicle is immobilized or stuck on the vertical geometry. Also referred to as lodged or high-centered. Interface ­ The broader area where a driveway joins the roadway, including the curved or flared turning areas. ITE ­ Institute of Transportation Engineers MUTCD ­ Manual on Uniform Traffic Control Devices. The federal MUTCD is incorporated by reference in 23 Code of Federal Regulations (CFR), Part 655, Subpart F. It is recognized as the national standard for all traffic control devices installed on any street, highway, or bicycle trail open to public travel in accordance with 23 U.S.C. 109(d) and 402(a). NCHRP ­ National Cooperative Highway Research Program Non-restrictive median ­ A median designed to be easily crossed by a motor vehicle, such as a two-way left-turn lane (TWLTL). Offset ­ The meaning of this term depends on the context. In the context of a driveway connec- tion transition, it can refer to the situation where due to the presence of on-street parking, a bicycle lane, a shoulder, or similar space generally parallel to and outside of the traveled way, the physical end of a driveway is some distance away from the edge of the traveled way. The effect of this is that part of the turning movement of those vehicles entering or exiting the driveway takes place in that area between the edge of the traveled way and the physical end of the driveway.