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2 CoNSUlianr Place ' <br /> P.O. Box 51013 KEENER ENgiNEERINq ASSOCIATES, INC. <br /> DURHAM, NC 27717 <br /> Phone: (919) 419-0350 CIVIL ANd TRANSPORTATION ENgiNEERINq <br /> fax: 919 490-8953 <br /> MEMORANDUM <br /> To: Mr. Werner Hausler, AIA <br /> The Homestead Group <br /> From: Ms. Donna Keener, P.E. <br /> Keener Engineering Associates, Inc. <br /> A preliminary analysis of the horizontal alignment of Road "D°, which connects Seawell <br /> School Road and Merin Road, was conducted. No consideration was given to the vertical <br /> constraints at this stage. The design assumptions used are as follows: <br /> Posted Speed of Roadway: 35 mph <br /> Design Speed of Roadway: 40 mph <br /> Design Speed of Roadway @ Intersection: 30 mph <br /> Maximum Superelevation: 0.06 ft/ft <br /> Guidelines: AASHTO 1990 Standards <br /> According to AASHTO guidelines, the minimum radius of the proposed roadway at the <br /> intersection with Homestead Road is 230 feet. The corresponding length of superelevation runoff <br /> is 90 feet. The runoff length is the distance required to transition from full superelevation to <br /> adverse crown. Normal practice is to place 213 of the runoff length on the tangent approach and <br /> 1/3 on the curve. The length of tangent runout is required in addition to the superelevation <br /> runout. The tangent runout is the length of transition from adverse crown to normal crown. In <br /> this case; the length of tangent runout is 30 feet. Therefore, the total tangent length needed to <br /> transition to normal crown is 90 feet. <br /> The horizontal curve which ties into Merin Road should have a minimum radius of 450 feet, using <br /> a design speed of 35 mph. Accepted practice is to design the roadway at a speed 5 mph in <br /> excess of the posted speed. The length of superelevation runoff for this curve is 115 feet, and <br /> the tangent runout is 38.3 feet. The total tangent length needed to transition from normal crown <br /> to full superelevation is 115 feet. <br /> Placing these two horizontal curves in the area planned for this roadway extension results in a <br /> severe "S-curve" through the parcel. There is no room for the tangent runout or superelevation <br /> runoff between the curves, and the result is an undesirable reverse curve. To meet the criteria, <br /> a tangent section of 205 feet is required. This length is not available under this scenario. A direct <br /> result of this reverse curve will be the extreme difficulty in locating safe driveways to serve the <br /> remaining parcel. Severe sight distance problems will undoubtedly arise. <br /> Because accepted engineering standards are impossible to meet, the preliminary analysis of this <br /> horizontal alignment shows that the resulting roadway will be both dangerous and <br /> undesirable. <br /> {-�McSTFAf� (7'r2�UP <br />