Introduction #

In road superelevation, shoulder slope treatment involves the modification of the shoulder’s gradient, aimed to enhance the vehicles’ maneuvering, and ensure proper drainage along the curves.

The shoulders are divided into two categories, High Side and Low Side, as in the image below.

How can it be applied in MiTS? #

With the introduction of MiTS 3.2, enhancements have been made to the shoulder slope behavior; It now supports a range of combinations for the Shoulder Low Side and Shoulder High Side of the curve, as in Civil 3D.

Steps to apply: #

1. In a project file, go to the Options tab and click on Project Settings

2. Expand the Road module settings

3. Expand Design and click on Superelevation

Shoulder slope in MiTS & Civil 3D #

Shoulder Low Side of The Curve #

Examples can be referred to based on this Project File.

Default Slope #

The shoulder of the low side will follow the default slope of 4.00% as in the example below.

In MiTS #

Refer to CH290.028

The gradient of the shoulder is displayed as 1:25.0, which is equivalent to 4.00%.

In Civil 3D #

Follow Carriageway #

The shoulder will be adjusted to match the slopes of the adjacent carriageway along the superelevation.

In MiTS #

The shoulder at the lower side of the curve has a gradient of 1:16.7, which follows the gradient of the carriageway.

In Civil 3D #

Breakover Removal #

As the carriageway is elevated or tilted around horizontal curves, there can be a sudden change in the slope between the shoulder and the carriageway. This creates a “breakover” that may result in drivers losing control once their vehicles veer off the road.

Therefore, it is necessary to eliminate this breakover by adjusting the shoulder on the lower side, making it more level and reducing the steepness of the gradient. This adjustment will create a smoother and safer transition between the carriageway and the shoulder.

In MiTS #

The slope changes on the shoulder at the low side can be observed between two consecutive chainages, CH264.00 and CH265.00. Note that the changes can be easily observed when the cross-section intervals are set at 1.00.

In Civil 3D #

Shoulder High Side of The Curve #

Examples can be referred to based on this Project File.

Default Slope #

By right, the shoulders of the high side will follow the default gradient of 4.00%

However, for the case of the high side, the shoulder behavior may be affected by the Maximum Shoulder Rollover, which can be applied under the Project Settings.

What is Maximum Shoulder Rollover? #

Shoulder Rollover refers to the variation in cross slope between the carriageway and the adjacent shoulder.

Typically, the carriageway is designed with a cross slope of 2.5%, which helps direct the runoff from the center crown towards the edge of the road. In contrast, the shoulders are usually sloped more steeply at about 4% to ensure the runoff is effectively directed to the roadside drainage system, preventing water from pooling near the pavement.

The difference in slope creates a “dip” or “rollover” where the carriageway meets the shoulder. If this transition is too steep, it can be hazardous for cars that drift off the lane at high speeds, leading to instability or loss of control.

To ensure safety on the road, the slope difference between the carriageway and shoulder will be governed by a threshold known as Maximum Shoulder Rollover, which should not exceed 8% according to the road design standards in JKR ATJ 8-86.

Applying Maximum Shoulder Rollover of 8% #

In MiTS #

Options > Project Settings > Expand Road > Expand Design > Superelevation > Ensure the Maximum Shoulder Rollover is checked > Input the maximum value

Shoulder Slope Calculation

\mathrm{Slope}=\mathrm{Carriageway}\;\mathrm{Superelevation}\;-\;\mathrm{Maximum}\;\mathrm{Rollover}

\mathrm{Slope}=\left[\left(\frac1{16.7}\right)\times100\right]-8\;=\;-2.01

** The -ve sign represents slope down

The slope is adjusted to 2.01% (equivalent to 1:50) as it is less steep than the default slope of 4.00%

In Civil 3D #

Applying Maximum Shoulder Rollover of 13% #

In MiTS #

**This example is just to show the shoulder behavior when the computed shoulder is steeper than the default slope

Shoulder Slope Calculation

\mathrm{Slope}=\mathrm{Carriageway}\;\mathrm{Superelevation}\;-\;\mathrm{Maximum}\;\mathrm{Rollover}

\mathrm{Slope}=\left[\left(\frac1{16.7}\right)\times100\right]-13\;=\;-7.01

** The -ve sign represents slope down

The computed slope of 7.01% exceeds the default slope of 4.00% (equivalent to 1:25.0), hence, no adjustment is made. The shoulder slope remains at 4.00% to prevent being too steep.

In Civil 3D #

Maximum Shoulder Rollover is NOT applied #

With the parameter not applied, the shoulder slope will remain the default value of 4.00%.

In MiTS #

In Civil 3D #

Follow Carriageway #

The slope of the shoulder will be adjusted to match the slope of the adjacent carriageway along the superelevation.

In MiTS #

In Civil 3D #

Conclusion #

With all the relevant settings configured correctly in MiTS and Civil 3D, the Road Cross-Section of MiTS will yield results identical to those of the Section View in Civil 3D, as shown above.

This indicates that MiTS and Civil 3D operate on the same design principles.