Basic Superelevation Rules of Thumb

1.  Always have report lock turned on when working with superelevation. This produces a report that includes lots of useful data.

2.  Non-Linear transitions require 1-1/2 greater transition length than linear transitions do for the same rate of change. Kentucky uses linear transition as the Inside and Outside Transition Mode.

3. The ‘Tangent Point:’ parameter is used only when a spiral is present in the transition. If Normal Crown is selected all the transition; both runoff and runout, occurs on the spiral, spilling on to a portion of the curve if necessary. If Zero Slope is selected the ‘tangent to spiral’ station will separate the superelevation runoff from the tangent runout.

4. Delta G is the rate of superelevation transition expressed as a percentage. Strictly, Delta G is the distance that the range point of the template rises during a given transition divided by the length of the transition. A 1:200 rate of change for 50 mph design would equate to a Delta G of 0.5.

Table Method

1. The `Deg Crv' column for the degree of curvature is completely ignored, so changing it has no effect whatsoever. Radius values less than or equal to the exact degree of curvature radius should be used in the tables. Do not round degree of curvature radius lengths up. Superelevation tables must begin with the longest radii, then decrease in length down the page.

2. There is a 40 entry limit to superelevation tables. There must be a `NC' entry in the table or the first super rate will be applied to curves with radius longer than the first entry; even though they may not require superelevation. Curves with radii that fall between the `NC' entry and the first super rate will have the first super rate applied.

3. Super rates are interpolated from the `Super Rate' column in the specified table based on radii except as noted above. Any curve tighter than the shortest radii gets the maximum rate.

4. Runoff lengths are not interpolated from neither the 2-lane nor the 4-lane transition length columns of a specified table. The table runoff length used will be the value associated with the table radius that is either equal to or less than the actual alignment radius.

5. Superelevation from the table method invokes some special circumstances in the `tangent point' parameters referred to above in Basic Superelevation Rules of Thumb. Refer to the left side of the Superelevation Runoff Flow Chart for clarification.

6. The superelevation tables delivered with InRoads yield results very close to superelevation calculated based on AASHTO method 5.

Templates

1. Correct superelevation on typical sections with curb and gutter can be achieved utilizing Rollover Locks. Imagine a 4 lane template that has 24' of pavement at 1/4 " per foot; 2.08%, and a 2' gutter that slopes at 1" per foot; 8.33% (curb and gutter has 30" width over all). The super elevation range is typically defined from gutter to gutter, so your super elevating 26' of travel-way on each side of the centerline. If the maximum super rate is set at something less than the gutter slope the low side gutter slope will stay at 8.33%. In InRoads, the super rate is based on the total vertical difference in the super range divided by the total horizontal distance defined in the super range, not the individual components. Assume e-max is 6.00%, and a curve warrants full super. The 24' pavement section on the low side of the curve will never attain full super; 6.00%, it will only be 5.8% because the gutter section is held at the defined value of 8.33%. To achieve the desired results the super range should be set at the lip of the curb instead of in the gutter. The trick to getting the high side gutter to spill is to use rollover locks set at 0% difference on only the outside portion of the curve. Utilizing this method the low side gutter will retain its proper slope, but the high side gutter will spill.

Superelevation Workflow for Kentucky Transportation Cabinet

1. Layout proposed horizontal and vertical alignments. Horizontal spiral lengths based on AASHTO minimum length runoff values.

2. Having created a superelevation definition in the active geometry file, create and define the Template Library and the Roadway Library.

3. From the Superelevation palette select Superelevation Rate Calculator. Under Settings select Rate Parameters. In the Superelevation Rate Calculator Parameters dialog box set the Rate Calculation Method: to Table Method, set the Rate Table Name: to the desired super table, the Column from Rate Table to either 2-lane or 4-lane as appropriate. The Round Rates to: option may be toggled on at this point. The Desirable Max Super Rate: will warn the designer if a preferred e-max is exceeded. The desirable max super rate may be less than the absolute max super rate. Setting the desirable max super rate equal to the absolute max super rate will result in no warning messages.

Upon completion of setting the desired parameters select the Close button. Press the OK button in the Superelevation Rate Calculator dialog box. The Review / Edit Superelevation Rates dialog box will appear on the screen displaying the calculated superelevation rates. The calculated superelevation

rates can either be accepted by pressing the OK button, or edited by selecting the Edit button. Upon completion of editing select the OK button.

4. From the Superelevation palette select Build Application Stations. Verify the active Horizontal Alignment and revise as necessary the Vertical Alignment, Active SuperAlignment and Roadway Definition. Under Settings select Default Params. The Superelevation Default Parameters dialog box will activate. Set the Inside Transition Mode: and the Outside Transition Mode: as desired. Make certain the Tangent Point: is Zero Slope and Maximum Delta G is toggled off. Zero Slope will ensure that the runoff is on the spiral. If Maximum Delta G is toggled on it could override the Tangent Point-Zero Slope control based upon the computed transition length. If Maximum Delta G is used and the computed runoff exceeds the spiral length, the runoff will begin on the tangent-spiral station. The %Runoff on Tangent:, Minimum Tangent Length: and Minimum Runoff Length: settings have no affect on the superelevation application station calculations in this configuration.

If rollover locks are to be used, select the Locks option in the Superelevation Default Parameters dialog box. The Shoulder Rollover Locks dialog box will activate. Configure the shoulder rollover locks in accordance with the proposed design, then select OK to accept the settings and dismiss the Shoulder Rollover Locks dialog box. The Superelevation Default Parameters dialog box will once again become active, select OK to accept the settings and dismiss the Superelevation Default Parameters dialog box. Press Apply in the Build Application Stations to initiate the superelevation application station calculations.

If there are no problems with the superelevation ranges the Build / Edit Application Stations dialog box will activate. If a superelevation range overlap occurs an Information dialog box will activate to notify the designer. Select OK in the Information dialog box and the Build / Edit Application Stations dialog box will activate. Overlaps may be resolved by either editing the application stations in the Build / Edit Application Stations dialog box, or by recompiling the superelevation based on a different e-max value and/or spiral length.

If the report lock is toggled on a Superelevation Application Station Calculations report will activate. This report is the easiest way to see how the super is being applied. If revisions to the superelevation transition lengths are deemed appropriate then the spiral lengths on the horizontal curves should be revised. All of the settings will be maintained within InRoads; you may want to save the preferences to reload and use on other projects, so only the basic steps to compute the superelevation must be repeated.