2. Electronic (Digital) Level
The slope of a curb ramp or a walkway can make or break its accessibility. People who use wheelchairs, walkers, and other mobility devices cannot safely use a curb ramp, walkway, or ramp that is too steep. The most effective and efficient way to measure the slope of a walkway is to use a two-foot long electronic (digital) level.
Digital levels are relatively inexpensive, easy to use, and extremely accurate if you read and follow the instructions provided by the manufacturer. For the digital level to perform accurately, you must calibrate it at the beginning of each day before using it to measure any slopes and recalibrate it before using it again if you drop it. Calibrating a digital level is usually simple, taking less than a minute once you read the manufacturer’s instructions.
Helpful Tips for Using a Digital Level
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Don’t assume you can tell if a running slope or cross slope is too steep without measuring. Even experts can misjudge how steep a running slope or cross slope is if they do not use a level.
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Make sure there are no pebbles or other debris under your level when you measure slopes and cross slopes. A small pebble or debris under a level can cause your slope measurement to be inaccurate.
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Electronic levels typically show measurements in three different ways: percentages (%), degrees (°), and ratios (1:8). It is important to keep your level on the same setting – we recommend percentages. If you do not keep your level on the same setting, you will have difficulty determining what your survey data means.
The ADA Standards set requirements for maximum running and cross slopes, so surveyors can generally check compliance with the Standards by measuring where the running slopes appear steepest and where the cross slopes appear steepest. If the running slopes and cross slopes at the steepest points comply with the requirements for maximum running and cross slopes, the running and cross slopes at other locations will also comply. The illustrated survey instructions for the features where slope and cross slope are likely to be an issue will show you how and where to take the measurements.
Note: Some architects use a "rise over run" formula to calculate the slope of a surface. This formula is useful when designing walkways and other surfaces, but it is not useful when assessing the accessibility of a feature that has already been constructed. This formula does not reliably provide the actual slope because it does not take into account factors such as the existing topography of a site and because it assumes that the slope over the length of the run is consistent, which is often an inaccurate assumption.
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