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Clear Zone Calculator

This module calculates the required clear zone width. Clear zone is the lateral distance from the edge of the traveled way that should be cleared of any fixed objects. Examples of fixed objects include: signs, trees, concrete structures, and utility poles.

  1. In the gray ribbon on top, select either a Fill Slope or Cut Slope
    1. A fill slope is when the roadway has been built above the original ground line
    2. A cut slope is when the roadway has been dug below the original ground line
    3. If the roadway is on original ground level, consider it a Fill Slope
  2. From drop down menu, select the range of Average Daily Traffic volume for the roadway from the drop-down menu.
  3. Select the Design Speed from the drop-down menu.
    1. If unknown, use the posted speed limit plus up to 10 additional miles per hour.
  4. Enter the slope along the right-side of the roadway (Vertical : Horizontal)
    1. For example, entering 1:4 means that the ground rises 1 vertical foot for every 4 horizontal feet
  5. Click the "Calculate" button
  6. The design clear zone width will be displayed in the white box.
  7. To remove all entries and calculations, click the "Reset" button.

By checking the box for "Horizontal Curve", you can add factors to adjust the clear zone width for roadway curvature.

  1. Check the box for "Horizontal Curve"
  2. In the gray ribbon on top, select either a Fill Slope or Cut Slope
    1. A fill slope is when the roadway has been built above the original ground line
    2. A cut slope is when the roadway has been dug below the original ground line
    3. If the roadway is on original ground level, consider it a Fill Slope
  3. From drop down menu, select the range of Average Daily Traffic volume for the roadway from the drop-down menu.
  4. Select the Design Speed from the drop-down menu.
    1. If unknown, use the posted speed limit plus up to 10 additional miles per hour.
  5. Select the radius of the curve from the drop-down menu
  6. Enter the slope along the right-side of the roadway (Vertical : Horizontal)
    1. For example, entering 1:4 means that the ground rises 1 vertical foot for every 4 horizontal feet
  7. Click the "Calculate" button
  8. The adjusted clear zone width for the curve will be displayed in the white box on the lower right corner.
    1. The design clear zone width for a tangent section with similar attributes will be displayed in the white box at the upper left. This is the same value that is calculated if the "Horizontal Curve" box is left unchecked
  9. To remove all entries and calculations, click the "Reset" button.
Approved
  

Lateral Placement Calculator

This module calculates the recommended offset distance for guardrail placement based on the roadway speed and minimum deflection distance based on the type of barrier installed. The first output is the offset to the "shy line" which determines how far from the roadway the barrier should be placed. The second output is the offset to the nearest roadside obstacle.

  1. Select the type of barrier to be installed from the drop-down menu.
  2. Select the design speed from the drop-down menu.
    1. If the design speed is not known, use the posted speed limit plus up to 10 additional mph.
  3. Click the "Calculate" button
  4. The minimum offset to the shy line will appear in the upper white box.
  5. The minimum offset to the nearest roadside obstacle will appear in the lower white box.
  6. To remove all entries and calculations, click the "Reset" button.

Notes on barrier type:

  • Flexible System barriers are the most commonly guardrail but require the largest offset to the obstacle.
  • Semi-Rigid Systems are used when the offset to the obstacle is limited.
  • Rigid Systems are used when the obstacle is very close to or against the roadway.
Approved
  

Run-out Length Calculator

This module calculates the run-out length for a vehicle leaving the roadway. The run-out length is the distance, parallel to the roadway, that a vehicle travels after leaving the roadway before it can come to a stop. This value is used to calculate the length-of-need of roadside barrier to protect errant vehicles from a hazard.

  1. Select the approximate design speed from the drop-down menu.
  2. Select the range of average daily traffic from the drop-down menu.
  3. Click the "Calculate" button
  4. The design length of run-out will be displayed in the white box.
  5. To remove all entries and calculations, click the "Reset" button.
Approved
  

​Barrier Warrants – Embankment Calculator

This module determines whether a roadside barrier (such as guardrail or concrete barrier) is warranted based on the height and steepness of the embankment and the roadway traffic volume. Other factors may warrant roadside barrier such as the presence of clear zone hazards. This calculator should not be misunderstood as being the only determining factor in the warranting of roadside barrier. It is only to determine if the embankment warrants barrier.

  1. Select the range of average daily traffic volume using the first drop-down menu
  2. Select the slope of the embankment from the second drop-down menu
    1. A higher horizontal dimension equates to a flatter slope
  3. Enter the height of the embankment in the right-most entry box
    1. This is measured from the top edge of the embankment down to the toe of the slope (in feet)
  4. Click the "Calculate" button
  5. The white box at the bottom of the module will display either "Barrier Warranted" or "Barrier Not Warranted".
  6. To remove all entries and calculations, click the "Reset" button.
Approved
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