TRUNCATED DOMES

The word “truncated”  is defined by the American Heritage Dictionary as “to shortened by as if by having a part cut off or to cut short” and the word “domes” is defined as “vaulted roofs having a circular, polygonal, or elliptical base and a generally hemispherical or semispherical shape”.

Prior to the implementation of curb ramps, the end of a walkway was detected by a drop off of the curb at an intersection. Weather an individual had perfect vision or was legally blind the drop off was the detectable warning at a hazardous vehicular way. When the drop off of the curb was removed and curb ramps became standard, a different warning had to be implemented and that is where truncated domes provide a detectable warning surface.

“Truncated domes” are often referred to as the “little bumps” located on curb ramps and transit boarding platforms and according to the US Access Board are the most effective system for providing a distinctive pattern detectable by cane and underfoot. Their specific function is to warn visually impaired people of hazards on a circulation path. Much like stop signs they warn visually impaired pedestrians to the presence of hazards in the line of travel, indicating that they should stop and determine the nature of the hazard before proceeding.

The specification for truncated domes can be found at: http://www.access-board.gov/adaag/dws/update.htm

The specified dome size is:

• Base diameter of 0.9 inches (23 mm) minimum to 1.4 inches (36 mm) maximum
• Top diameter of 50% of the base minimum and 65% of the base diameter maximum

The specified dome spacing is:

• Center-to-center spacing of 1.6 inches (41 mm) minimum and 2.4 inches (61 mm) maximum and a base-to-base spacing of 0.65 inches (16 mm) minimum measured between the most adjacent domes on a square grid pattern

Since 1991 truncated domes have been required on the edge of rail platforms in the USA and on curb ramps since 2001. They are here to stay and must be compliant throughout the life cycle of the structure in which they were made a part of. Implementing the highest standard of products available will ensure the lowest life cycle cost, the longest properly functioning product and provide a community with proper access. To view performance specifications refer to www.armor-tile.com

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