Session 3 Engineering and Aesthetics
Engineering vs. Aesthetics Source: City of Bellevue, “Speed Hump: Design, Pavement Marking, and Signing”
Design of Horizontal Measures • R = V2/15(e+f) • R = radius of a horizontal measure (ft) • V = speed of travel through the measure (mph) • e = superelevation rate of road • f = side friction factor
Design, Operating, & Posted Speeds Critical Point Design Speed Mean Operating Speed Posted Speed Limit AASHTO Design Speed Tangent Curve Tangent Curve Tangent ALIGNMENT
Maximum Curve Radii for Various Desired Speeds Desired Speed Assumed Side Friction1 Assumed Superelevation Maximum Radius • 15 mph 0.38 0.00 43 0.00 88 • 20 0.30 • 25 0.25 0.00 167 • 30 0.22 0.00 273 1Based on American Association of State Highway and Transportation Officials (AASHTO), A Policy on Geometric Design of Highways and Streets, Washington, D.C., 1990, Figure III-17 and Table III-17.
Another Constraint -- Long Wheelbase Vehicles Source: KPG, Inc., Design Report for SE 46th Way Traffic Control Improvements, City of Bellevue, WA, 1994.
Design of Vertical Measures • A = 2.15V2/R R = V2/5.81 • A = acceleration (ft/sec2)V = speed of travel over a vertical measure (mph)R = radius of the measure (ft)
Landscaping Policies Agency Neighborhood Dayton, OH install maintain Eugene, OR install maintain till volunteer dies/moves Gainesville, FL install maintain choose plants from city nursery Howard Co., MD install & maintain Montgomery Co. install maintain choose landscape palette San Diego, CA install maintain choose plants from approved list Tallahassee, FL install & maintain reconsidering because of “uglies”
MUTCD General Guidance • ... engineering judgment is essential to the proper use of signs, the same as with other traffic control devices • Information of a less important nature and extraneous information should be moved to less critical locations or deleted • A conservative use of regulatory and warning signs is recommended as these signs, if used to excess, tend to lose their effectiveness • In situations where messages are required other than those herein provided for, the signs shall be the same shape and color as standard signs of the same functional type
MUTCD Operational Guidance • Yellow diamond-shaped signs for warning • Yellow lines separating opposing traffic • Lettering or symbols of adequate size • Short legends • Symbols in preference to word messages • Educational plaques with new specialty signs • Advance warning when high driver judgment or deceleration to a specific speed is required • Size, height, position, lettering, and reflectorization per MUTCD