Office of Federal Lands Highway

Roadway Designer Manual: 7 - Overlay Tools

Introduction

The Overlay Tools within Roadway Designer are a set of tools to facilitate the design and optimization of widening and resurfacing projects. The tools are only available for use when Roadway Designer’s Display Mode is set to Overlay. These commands aid in the design of overlay projects where there is a need to adjust the vertical alignment and to minimize volumes of overlay and milling. The goal is to optimize the milling and asphalt quantities and improve the vertical profile to achieve the optimal design profile.

Figure 1

Tools

Each tool performs a particular function on the Roadway Designer data to ultimately produce an optimized cross slope and vertical alignment.

Figure 2

There are three essentially separate technologies that can be used for Overlay Solutions:

• Overlay/Stripping Components
• Cross Slope Optimization
• Vertical Adjustments

From a software standpoint these technologies are completely separate. Cross Slope Optimization has little to do with Templates or with Vertical Adjustments. Overlay/Stripping components work identically whether Vertical Alignments or Vertical Adjustments are used. Vertical Adjustments pay no attention to anything in a template other than the top layer. Overlay/Stripping Components have no effect on the Adjustment methodology or results.

From an engineering perspective, these three technologies are closely related in providing a solution. Quantities are calculated from template components, Overlay/Stripping components are obligatory for accurate quantities. Vertical Adjustments are used to calculate, define and refine a vertical alignment that optimally meets the design or cost criteria. The Cross Slope Optimization tools provides an automated way to meet design criteria and provide full control of the new rehabilitated surface’s cross slope.

Cross Slope Optimization

The Cross Slope Optimization tool produces a Roadway Designer Superelevation Control Line that controls the cross slope between two template points. The Control Line can be used on any template component type, not just in conjunction with an Overlay/Stripping component. There is no requirement to use Overlay/Stripping components or Vertical Adjustments after using the Cross Slope Optimizer.

Figure 3

If the Vertical Adjustments tools are to be used with optimized cross slopes, then the Cross Slopes must be optimized prior to running the Vertical Adjustments. In order to adjust the Vertical based on a new, optimized cross slope, the optimized slopes must available to the Vertical Adjustment tool.

When building new roads, cross slopes are defined in accordance with best safety and driver‐experience practices, including optimized normal crown slopes and superelevation according to approved agency standards. Deviations due to crossing streets, drainage requirements, and other location‐specific needs are evaluated and incorporated into the design.

Safety, consistency and pleasant driver experience are again major considerations when rehabilitating existing roads.  A primary goal is to move the existing geometry towards the ideal geometry. The primary constraints of cost and constructability limit how far the geometry can be moved from the existing towards the ideal. Generally, the amount by which the slope can be optimized is expressed in a maximum slope change or maximum elevation difference from the existing pavement.

The Roadway Designer Cross Slope Optimization (CSO) Tool is designed to automate solutions to these challenges.

Superelevation Control Lines

Fundamentally a Superelevation Control Line is simply a list of cross section slopes defined by station. Reading a superelevation control line at a given station shows the cross slope at that station.

Point Controls connect a Superelevation Control Line to a template, designating a pivot point and rotating point. Given that Superelevation Control Lines are simply cross section slope lists, they are perfect for Cross Slope Optimization needs.

A Superelevation Control Line can represent:

• The existing cross slopes along a corridor
• The ideal cross slopes along a corridor
• The final design cross slope along a corridor

The Cross Slope Optimization tool breaks down into logical parts:

• Reads the existing cross slope
• Gets the ideal cross slope definition from the user
• Gets the deviation‐from‐existing Tolerance limits from the user
• Calculates a design cross slope
• Allows edits to the calculated results
• Provides a usable output: a Superelevation Control Line

The functional result of this tool is a single standard Superelevation Control Line. Recall that a Superelevation Control Line defines cross slope at stations. The resulting Control Line can be used as the Roadway Designer Point Control to define the corridor cross slope. Left and Right side slopes must be computed individually and a Control Line created for each.

Existing Slope

The Existing Slope is calculated at each corridor template drop from the active surface, which should be the existing ground surface (no attention is paid to the template itself). The user defines two lines along the corridor to determine the offset locations of the surface elevation samples.

The purpose of the Cross Slope Optimization dialog is to create a new Design Cross Slope, subject to limits from the existing ground. The dialog is set up to design one cross slope, one side at a time. In order to design both the left and right sides, the workflow will need to be performed twice.

For the Existing Ground Cross Slope Definition, the software reads the Active Surface elevation at two locations. Between the points, a slope is calculated. Define either Horizontal Alignments or Features in the Active Surface for the horizontal locations. The elevations are always read from the Active Surface.

Figure 4

Ideal/Theoretical/Optimum Slope

The Ideal/Theoretical/Optimum Slope is defined in the part of the dialog titled Design Cross Slope Definition. The Definition can be either a single keyed‐in value or a Superelevation Control Line.

For the Design Cross Slope Definition, there is a choice of comparing to a constant cross slope or to a Superelevation Control Line. A Superelevation Control line is, in essence, a list of cross slopes by station. For all but the simplest roads, using Superelevation Control lines is easier.

If a Control Line exists representing the Ideal Cross Slope, simply select it. If one does not exist, creating one is easily accomplished.

Figure 5

The Cross Slope Optimization (CSO) tool itself can be used to create an Ideal slope Control Line. It creates a Control Line along the existing ground and within a user specified Tolerance. Setting the Tolerance to zero outputs a Control line that exactly matches the existing ground. Using superelevation editing techniques, this line can be edited from the existing state to represent an ideal state. The challenge with this approach is that there is no direct correlation to the ideal design standards. They must be adjusted manually. The control line may also be littered with too many irrelevant datapoints that would need to be edited out.

A far easier approach is to use the Create Superelevation Wizard to quickly create an intelligent control line and then to edit it as details dictate.

Design Slope

The results of the tool can be saved as a New Control Line as defined in the New Control Linesection of the dialog.

Figure 6

Just because an ideal standard cross slope can be computed, does not mean that the existing conditions can or should be modified to that standard. Design changes need to be subjectively evaluated for a number of reasons, including cost. Standard practice may dictate that resurfacing should not adjust the existing cross slope beyond some maximum value. The CSO tool allows the user to key in a Slope or Elevation Tolerance. An Elevation Tolerance limits the elevation difference between the existing and design surfaces at the pavement edge.

Another common design constraint is limiting the Delta G ‐ how quickly the cross slope can change longitudinally along the corridor. If the CSO calculates cross slopes that violate the user‐defined Delta G, the software highlights where these excesses occur. The software does not automatically adjust the cross slope to meet the Maximum Delta G, but makes it easy for the user to do so.

The results of the CSO calculations can easily be overwritten by the user.

Once the user has defined the settings for the existing and target cross slopes and the Optimization Parameters, clicking the Calculate Correction button will compare the slopes at each template drop, showing the results in a table.

The Results table shows, for each station where a template is to be dropped:

• Ground Slope
• Ideal Slope
• Difference between the two
• Corrected (Design) Slope
• Delta Elevation
• Delta G

The Corrected Slope is the slope that gets passed to the New Control Line for use in Corridors. The Corrected Slope is calculated according to the following rules:

• The difference between the Existing and Design/Ideal slopes is calculated
• If the difference is less than the Tolerance, then the Corrected Slope is the Design/Ideal slope
• If the difference is greater than the Tolerance, then the Corrected Slope is the Existing Slope adjusted towards the ideal by the value of the Tolerance

The user may override any of the Corrected Slope value individually or by selecting multiple Corrected Slope values. Cross Slopes that are Adjusted, if any, can be scrolled to by clicking the left and right arrows. The largest adjustment can be scrolled to by clicking the Largest button.

Slopes are not adjusted to meet Delta G criteria, but Delta G values exceeding the Maximum are highlighted in red. Delta G Errors can be scrolled through using the Left and Right Delta G Error arrows.

Adjusted Cross Slopes

The buttons next to Adjusted Cross Slopes allow skipping to Stations with slopes that are outside the Slope or Elevation Tolerance. If no stations have slopes deviating from the ideal by more than the allowed Tolerance, the buttons remain disabled.

Figure 7

When using CSO to create a new Control Line, two things will occur. First, a new Superelevation Control Line will be created and displayed in the Superelevation Diagram view. Second, if the Design Cross Slope Definition Design Type was a Control Line, the program will attempt to replace the super elevation point control that uses the specified control line with the newly‐created control line.

If it is successful, the program will not remove the previous point control, but will merely disable it.

Figure 8

Vertical Overlay Adjustment Settings

Vertical Adjustments read the top of the template and the existing ground to move the template vertically as per the user‐defined Overlay and Milling settings. The Cross Slope of the template has an effect on the adjustment values.

Figure 9

To apply adjustments based on Cross Slope Optimization results, the Cross Slope Optimization workflow needs to be performed prior to Vertical Adjustments.

The Adjustment methodology pays no attention to the types of components making up the template. The adjustments are identical regardless of whether Overlay or Stripping components are used. Proper quantities, however, do require Overlay and Stripping components.

Figure 10

Once the Vertical Adjustments produce a design requiring saving, a Vertical Alignment needs to be created and saved to the Geometry Project file. The Smooth Vertical Alignment and Apply Vertical Alignment command are used for this.

Vertical Adjustment Options

The Vertical Overlay Adjustment tool provides solutions for the most common resurfacing practices:

• Minimum Overlay
• Minimum Overlay with Maximum Milling
• Minimum Milling
• Minimum Milling with Maximum Milling

The pavement design can be complex, including leveling layers and cheaper binder courses. Regardless of the complexity of the design sections, the Roadway Designer Vertical Adjustment methodology is based on a few simple factors.

Figure 11

Backbone – the rehabilitation section as required in the specifications. The backbone thickness is constant. Variations in total thickness across the width of the template occur below the backbone. The Roadway Designer defines the backbone from the top of the template between user‐defined left and right points. Only the surface which creates the top of the template is used for analysis, any template components under the top are not used in the calculations.

Backbone Thickness – the backbone is assumed to have a constant depth across its width. For calculations, the Backbone Thickness is measured upward from the backbone.

Minimum Overlay Thickness – the minimum thickness to be maintained between the bottom of the Backbone and the existing surface, including any new milling. The overlay section must maintain a minimum thickness for structural integrity. At points across the section, the thickness may exceed the minimum thickness due to irregularities in the existing cross section. This is expected and is generally not a structural concern.

Minimum Milling– the lowest vertical adjustment where the existing surface and backbone bottom intersect. This position would require the least amount of milling across the full width of the backbone.

Maximum Milling Depth Adjustment– the maximum vertical distance to mill out high spots in the existing pavement.

While Cross Section display and accurate material quantities require close coordination between Vertical Adjustments and Overlay/Milling components, the Vertical Adjustment Methodology does not. Other than determining the template Backbone top, so that it can compute a Backbone bottom, it pays no attention to the template components.

Figure 12

The user defines the left and right limits to the surface comparison and whether to include all the existing surface points or just the template vertices. Given the surface top and the existing surface, the software finds the critical vertical difference value and applies the appropriate user‐defined Overlay or Milling values.

Vertical Comparisons

When the Adjustments are run, the vertical differences between points across the comparison range are computed. There are two comparison methods: Template Points Only and All Cross Section Points.

Figure 13

The first method performs the difference calculations only at the template points. The second calculates the differences at every template point and every point in the existing surface. In order for potholes or other existing surface irregularities to be taken into consideration, choose the All Cross Section Points method. When running Vertical Adjustment, a red box is drawn around the critical point at each station for feedback purposes.

A Maximum Difference can be set to limit the range of adjustments. A Maximum Difference specifies that no vertical adjustment between processed stations will exceed this value (absolute).

 If this value is 0.0, there will be no limit on the vertical adjustment.

For every comparison point, the vertical difference between the existing surface and Template Top is calculated. Direction/sign matters:

• Positive = Existing Surface above Template Top
• Negative = Existing Surface below Template Top

There are only two comparison points that matter, the Zero Overlay Point and the Minimum Milling Point.

Minimum Milling Point

• Used only for the Use Minimum Milling option.
• The highest point at which the milling occurs across the full width of the Template Range.
• Located at the point where the difference is the lowest value.
• Minimum Milling Delta = lowest value (sign matters).

Zero Overlay Point

• Used for Minimum Overlay options.
• The highest point at which the overlay occurs across the full width of the Template Range.
• Located at the point where the difference is the highest value.
• Zero Overlay Delta = highest value (sign matters).

Template Range

For the Proposed Pavement, the user must define the left and right end points of the template from the list of the templates points. This is known as the Template Range.

Figure 14

For defining the comparison width of the existing surface, there are a number of options the user can select:

• Match Template Range – the width defined for the template range will be used for the existing surface.
• Match Existing Ground Features - (InRoads only), Alignments, or Styles
• Fixed Offsets – specify fixed left and right range offsets from the center line of the design.

Match Template Range or Fixed Offsets are quick and easy options, but will more than likely have some “slop” in them.

In most surveys and their resulting surfaces, the existing Edges of Pavements are identified. These features, if available, should be incorporated into the existing model, as alignments. Once modeled they can be used to define the limits of the valid existing pavement comparison range as Styles, or Alignments.

Vertical Adjustment Geometry

Once the appropriate Critical Point and its signed Vertical Difference is calculated, the Vertical Adjustment is calculated using the following equations (An adjustment value is calculated at each Template Drop station). :

Minimum Milling	Min. Milling Delta + Backbone Thickness
Minimum Milling with Maximum Milling	Min. Milling Delta (not exceeding the Maximum Milling Value) + Backbone Thickness
Minimum Overlay	Zero Overlay Delta + Backbone Thickness + Minimum Overlay Value
Minimum Overlay with Maximum Milling ‐ Positive Adjustment	Zero Overlay Delta + Backbone Thickness + Minimum Overlay Value ‐ Maximum Milling Value
Minimum Overlay with Maximum Milling ‐ Negative Adjustment	Zero Overlay Delta + Backbone Thickness + Minimum Overlay Value ‐ Maximum Milling Value where the Milling adjustment is limited so that the overall adjustment is zero or greater)

It is important to note that for other than defining a Template Top comparison line, the adjustment methodology pays no regard to the template or its components.

A Vertical Alignment does not need to exist for the Adjustments to be calculated. With the Corridor Vertical set to None, the initial PGL elevation is assumed to be zero. The adjustment will be equal to the new PGL elevation.

Except for the Minimum Overlay with Maximum Milling option, the vertical adjustment methodology and results are identical whether the PGL is above or below the existing pavement or whether a vertical alignment is used at all. For the Minimum Overlay with Maximum Milling option, the Milling Adjustment is limited so that it does not cause the Overall Adjustment to be negative.

Minimum Milling ‐ without Maximum Milling

 

Figure 15

Minimum Milling ‐ Without Maximum Milling

• Provides milling across the full width of the Template Range.
• Requires the least amount of milling for full‐width milling.
• Located at the point where the difference is the lowest value (bottom‐most).
• The Minimum Milling “line” represents the bottom of the new template backbone.
• Minimum Milling Delta = lowest value (sign matters).

When the Use Minimum Milling option is selected the Minimum Milling Point is found as the Critical Point. The Minimum Milling Delta is used in the adjustment calculations.

Backbone Thickness

The logic behind defining a Backbone Thickness is that the Plan Grade Line (PGL) is generally at the top of a template, and overlay and milling is generally a based on the bottom of a fixed component. A Backbone Thickness value reconciles this geometric difference. The thickness is assumed to be uniform across the full width of the backbone.

The area between the top and bottom of the backbone is not used for volume calculations, milling operations, or even adjustment calculations. The only property used in calculations is the positive value of the Backbone Thickness. It is always added to the vertical adjustment sum.

The Backbone Thickness:

• is always a positive number
• is added to the adjusted PGL elevation
• can be controlled along the corridor with a parametric label or with multiple corridors segmented by Station Limits.

When keying in this value, the Vertical Adjustment dialog only accepts a positive number. This value is always added to the Adjustment Value.

Note that the software does not do any verification against the template.   The software assumes that the keyed‐in value is correct.

Parametric Labels for Backbone Thickness

 In the Vertical Overlay Adjustment Settings dialog, there is a field next to Backbone label for selecting a Parametric label.

Template Components may have their thicknesses defined either in a top‐to bottom or bottom‐to‐top direction. If defined in a top‐down direction, it is opposite the upward definition of the Backbone. When using Parametric Labels for the Backbone Thickness in this scenario, select the Parametric Label from the list then type a minus sign (‐) in front of the Label.

Minimum Milling + Backbone Thickness

Once the Minimum Milling Delta is found, the Backbone Thickness is added to provide the Vertical Adjustment value. In equation form: Adjustment = Minimum Milling Delta + Backbone Thickness

Minimum Overlay ‐ Without Maximum Milling

The Minimum Overlay scenarios are similar to the Minimum Milling scenario with the addition of a Minimum Overlay value and, optionally, the Maximum Milling value.

Figure 16

Rather than using the Minimum Milling Point, the critical point for the Overlay scenarios is at the Zero Overlay Point.

Zero Overlay Point

• Provides overlay across the full width of the Template Range.
• Requires the least amount of full‐width overlay.
• Located at the point where the difference is the highest value (topmost).
• Zero Overlay Delta = highest value (sign matters).

Overlay Settings

Overlay/Milling Thicknesses

The Minimum Overlay value is added to the Zero Overlay vertical difference to provide the Vertical Adjustment value. If a Maximum Milling value is set, this value will be subtracted from the Adjustment value.

It is important to note that while a final, plottable and “quantity‐precise” solution requires template components that are consistent with these values, the Vertical Adjustment calculations ignores the template components under the template Top. The entirety of Vertical Adjustment calculations are based on the settings described above.

Minimum Overlay

When the Use Minimum Overlay option is selected, the Minimum Overlay Value is added to the Zero Overlay Delta value.

Figure 17

While the Zero Overlay Delta value may be positive or negative (up or down), the Minimum Overlay Value is always positive and is always added to the Delta Value.

Minimum Milling with Maximum Milling

The Zero Overlay Point is the lowest point at which the overlay occurs across the full width of the Template Range and is also the highest point at which milling occurs. Setting a Maximum Milling value limits how much milling occurs downward from this point.

Figure 18

When set with the Minimum Milling option, the milling adjustment value is limited by the higher of the Maximum Milliing value or the Minimum Milling Point.

Minimum Overlay with Maximum Milling

Existing pavement surfaces tend to be irregular, with bumps and potholes. Very often, milling out the high spots saves considerable amounts of overlay material while still maintaining the minimum required overlay thickness.

Figure 19

The Roadway Designer Vertical Adjustment tool allows a Maximum Milling Value to be set for Minimum Overlay Adjustments. When set, the tool provides a Minimum Overlay solution with high points milled out up to the specified Maximum Milling Value.

Minimum Overlay with Maximum Milling takes the Minimum Overlay adjustment solution and subtracts a milling value from it. The subtraction of the Milling Value is the last operation in the Adjustment computation, occurring after the Zero Overlay Delta is computed and the Minimum Overlay Value and Backbone Thickness are added.

In addition to the Milling amount being limited by the user‐defined Maximum Value, the Milling adjustment value is limited by the PGL.  The Overall Adjustment value cannot be made negative by the Milling.-adjustment-. Unless the PGL limits the Milling Adjustment, the Maximum Milling Value will be used in the Adjustment calculations.

Saving the Vertical Adjustments

The elevation of the template is controlled by one of two methods:

• Corridor Control – Vertical Alignment or Feature
• Vertical Adjustments

If the Roadway Designer mode is set to Overlay and the Vertical Adjustment Settings dialog is properly set, then the elevation is controlled by the Vertical Adjustment settings. Otherwise, the elevation is controlled by the Corridor.

As long as the Vertical Overlay Adjustment Settings is controlling the elevation of the template, the Corridor Vertical definition has no effect on the location of the template. The Corridor control does, however, affect the Vertical Adjustment Value.

When the Roadway Designer Display Mode is set to Normal or Superelevation, however, the Vertical Alignment does control the elevation of the template. To use the Adjustments for most workflows, a vertical alignment should be saved from the Adjustment results.

Smooth Adjusted Vertical Alignment

The first step in creating a vertical alignment from the Adjustment values is to use the Smooth Adjusted Vertical Alignment tool.

Figure 20

This tool is used to create a best fit (regressed) vertical alignment from the active adjustment values.

In addition to a field to key in a Name for the new Alignment, there is a field for keying in a design Tolerance. This Tolerance value sets the maximum allowable difference above or below the exact PGL line created by the Adjustment values.  The smoothed vertical alignment will fit within this envelope.

Figure 21

The smoothed vertical alignment will fit within this envelope.

If the new vertical alignment is to exactly represent the Adjustment values, run this command with the Tolerance set to 0.0.

Clicking Apply, the regressed alignment is displayed in the profile window along with an envelope line that represents the maximum distance the regressed line can be away from the Adjustment results.

The Create Linear Elements Only check box, when checked, creates only linear elements (tangents). When unchecked, the software attempts to fit parabolic curves in where possible.

Be aware that non‐tangential vertical curves are possible using this option. In any case, once the adjustment is saved as an alignment, any of the InRoads /GEOPAK editing tools can be used.

Apply Adjusted Vertical Alignment

After Smoothing the Vertical Adjustment, the vertical alignment at this point is known only to Roadway Designer; the Vertical Alignment has not been added to the active Geometry Project data.

Figure 22

The Apply Adjusted Vertical Alignment tool takes the Adjusted Vertical Alignment active in the Roadway Designer, assigns it a user‐selected Style, and creates the Vertical Alignment as a child of the Active Horizontal Alignment.

Figure 23

Bottom of Envelope and Top of Envelope vertical alignments can be created and assigned, based on the previously keyed in Tolerance value.

When the Apply Adjusted Vertical Alignment to Corridor option is selected:

• The selected style will be applied to the regressed vertical alignment
• The alignment will be added as a child to the corridor's horizontal alignment
• The corridor will be modified to use this new vertical alignment In addition to the Milling amount being limited by the user‐defined Maximum Value, the M

Curves created by the Apply Adjusted Vertical Alignment tool may not be Tangent.

Given that the intent of smoothing adjustments is to minimize the washboard effect, the  non‐collinearity is normally acceptable.

In any case, standard vertical alignment editing commands can be used to clean up the alignment as necessary. The Tolerance alignments can be used as a guide during such edit.

Conclusion

Advantages:

• The Overlay Tools facilitate the design and optimization of widening and resurfacing projects.
• These commands aid in the design of overlay projects where there is a need to adjust the vertical alignment to minimize volumes of overlay and milling.
• Ideal cross slopes are easily calculated

Uses:

• When there is a need to calculate the optimum cross slope and vertical alignment for minimizing overlay and milling volumes for a resurfacing project.

Workflow:

To access this workflow, follow this link: Overlay Tools Workflow

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