![]() ![]() Type I sheeting has the lowest performance of all Types. Modern versions may be of a prismatic construction. Historically it has been composed of enclosed-lens glass-bead material. Type I is an engineering grade, retroreflective sheeting.To check this former property in the lab, the coefficient of retroreflection is evaluated for light coming from different places, for instance at two entrance angles of -4 and 30 degrees. Retroreflective sheeting must also retain this property regardless of the direction of the light source as the approaching vehicles could be in a variety of approach paths. Therefore, sign sheeting should return the incident light in the general direction of the light source where the driver is also expected to be. In practice, this would send the light back to the headlight and would not work for a driver. A “perfect” retroreflector would reflect the light back to where it came from that is exactly opposite the incidental path regardless of the relative orientation between light source and sheeting. The ratio of the perceived brightness (luminance, cd/m²) to that of the intensity of the incident light (lx) measured on the surface of a retroreflective material is known as the “coefficient of retroreflection (cd/lx/m²)”. For more detailed information on this, see the MN MUTCD, Table 2A.3 Sign Color, Sheeting Type, Additional Criteria, on page 2A-6 (PDF, 60.89 MB). In addition, the material of these signs shall be one of two categories: Beaded Sheeting for ASTM Types I, II or III, and Prismatic Sheeting for ASTM Types III, IV, VI, VII, VIII, IX, or XI 5. A guide sign provides directions to road users, including routes, destinations, and distances.Īll these signs “shall be retroreflective … or illuminated … of the same shape and similar color by both day and night …” ( section 2A.7 Retroreflectivity and Illumination, page 2A-3 (PDF, 60.89 MB)) 4. A warning sign calls attention to an unexpected condition, such as a sharp turn in the road or a school zone.Ĭ. A regulatory sign shows traffic laws or regulations such as stop signs and speed limits.ī. In Minnesota this cumulates in the Minnesota Manual on Uniform Traffic Control Devices (PDF, 60.89 MB), also known as the MN MUTCD.įor example, the MN MUTCD classifies three types of signs ( section 2A.5 Classifications of Signs, page 2A-2 (PDF, 60.89 MB)) 3:Ī. States may issue additional regulations or a supplemental manual on traffic control devices. The MUTCD sets minimum standards, provides guidance, and ensures uniformity of traffic control devices across the states 2. ![]() ![]() In the United States, the Department of Transportation Federal Highway Administration issues the Manual on Uniform Traffic Control Devices (MUTCD). ![]()
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