Morrisville Engineering, Design, and Construction Manual - July 2016

Section 4: Access and Circulation 4.2 Streets and Alleys 4.2.7 Street Intersection Design

e. The measurement method for determining the sight line for left, right, and through movements from the side street is based on NCDOT values and illustrations. f. The measurement method for determining the sight line for left turns from the median lane of the through street is based on values listed in AASHTO’s “Policy on Geometric Design of Highways and Streets.” Objects Allowed in Intersection Sight Distance Areas Within intersection sight distance areas, development and landscaping shall be restricted to enable motorists approaching the intersection to see and react to vehicular traffic approaching the intersection from other directions. Any object placed within an intersection sight distance area shall comply with the following: 1. The object located may not significantly obstruct the required visibility of the driver. The driver shall be able to see over, under or around some objects within intersection sight distance areas. 2. Objects 12 inches in diameter and smaller, such as sign posts, may be allowed within sight distance areas if located so as to not substantially restrict the driver's view. 3. Objects such as fire hydrants, utility poles, and traffic control devices are permitted with minimal visual obstruction. Intersection Sight Area Obstructions The vertical line of sight between a motorist approaching an intersection an object approaching the intersection from other direction is a visual line connecting the driver’s eye, which is located 3.5 feet above the roadway surface, with the approaching object, which is located 4.25 feet above the roadway surface. If this line of sight is impeded by any obstructions, either the obstruction should be moved or the alignment adjusted by the Town of Morrisville (within Town-maintained rights-of-way), NCDOT (within State-maintained rights-of-way), or the property owner, as appropriate. 1. See Section 5.8.6.E.3, Street Intersections, of the UDO for minimum street intersection spacing standards and median break standards. 2. Whenever possible, streets shall intersect at right angles, as measured by the intersecting street centerlines. The minimum desirable intersection angle is 80 degrees. At no time shall a street intersect any other street at less than 75 degrees. 3. Curb radii shall be designed to satisfy the turning radius of the predominant design vehicle using the roadway. Minimum radii are listed in Table 4.2.7, Horizontal and Vertical Controls. 1. Turn bay tapers shall be straight line at a minimum ratio of 15:1 for posted speeds of 45 miles per hour and more. 2. The minimum turn bay taper allowed is 8:1 for posted speeds below 40 miles per hour. 3. Symmetrical reverse curve tapers are recommended for non-thoroughfare streets as shown in the details. 4. Storage lengths for the turn bays shall be calculated using NCDOT or other method approved by the Town Engineer. Medians Streets with medians shall be designated to allow for proper turning movements for a SU (single unit truck) design vehicle. AASHTO guidelines should be followed for the actual median design and median opening dimension. Turn Bay Tapers Street Intersection Design General

4.2.7.

Morrisville, NC

July 2016 Page 17

Engineering, Design, and Construction Manual