How to Simulate U-Turn in MiTS

U-turn is a type of turn that allows the road users to go in the opposite direction without obstructing the traffic. U-turn is applied where it deems safe and should follow the minimum guidelines to ensure the safety of all road users and the efficient movement of traffic.

This article will outline the modelling technique steps for one of the direct U-turn layouts from ATJ.

Steps to Design U-turn #

Sample project file

**Please note that the sample project file is created not following the usual real life road width or the minimum distance table in ATJ.

The key for the modeling technique of  U-turn in MiTS is to separate the network into four different roads with different centerlines. The left and right carriageway will be separated and each having their own centerline. Then, the two turns for each side will be connected as junctions as illustrated in the image below.

Step 1: Define the Roads and Centerline for Left and Right Carriageway #

• Add the Horizontal alignment for left and right carriageway, Horizontal > Line > Add (Project View). Make sure to set the design standard under Spread Input.

• Set the Design Standard for the curve as well, Horizontal > Curve > Spread Input. Please note that you will need to change the Design Standard, Design Speed, Design Radius and Spiral Length to suit the road network.

• If the road network requires a design radius smaller than Min. Radius stated under the Spread Input, go to Properties tab at the RHS panel > Change the Min. Radius Standard from JKR to None.

Step 2: Create Transition Lane by Using Sub-row Feature #

• Set road entities accordingly following your centerline using the Road Width button. You may refer to our Road Width User Manual for detailed steps on how to add road offset.

• Now, we will need to add the transition lanes which are for merging and diverging from the U-turn. For this purpose, we will use the sub-rows feature that is available in our road module. Identify the road entities where we will add the transition lane and add the sub-rows accordingly.

• Now, you may set the sub-row width with the chainage accordingly. At the center part, make sure you left the space for the connection with the turns.

Step 3: Define the Roads for Left and Right Turns #

• Add the Horizontal alignment for the left and right turns, Horizontal > Line > Add (Project View). Please make sure that the turns centerline intersect with the centerline for left and right carriageway. Do not create the junction at this stage yet as we will connect them manually in Step 4. Set the design standard under Spread Input as well.

• Set the Design Standard for the curve as well, Horizontal > Curve > Spread Input. Please note that you will need to change the Design Standard, Design Speed, Design Radius and Spiral Length to suit the turns.

• If the turn requires a design radius smaller than Min. Radius stated under the Spread Input, go to Properties tab at the RHS panel > Change the Min. Radius Standard from JKR to None.

• Set road entities for your turn following your centerline using the Road Width button. You may set the U-turn width accordingly.

Step 4: Connect the Turns as Junction #

• Now, we will be able to connect the turns and the carriageway as junctions. Click Junction > Select the Centerline of the Carriageway > Select the Centerline of the Turns. Please note that centerline can be selected when the cursor turn to  👆🏻 symbol.

• Then, you may set the radius accordingly under the Spread Input.

Step 5: Define the Vertical Alignment #

• Then, you may start to design your vertical alignment for all roads including the carriageway and turns (Vertical > Line). The blue line is indicated as your ground level (from imported survey points).

• Possible verification error for vertical alignment is the junction having different road elevations. In this case, you may double click the verification error and you will be directed to the error. Then, you use the Auto Adjust button to solve the error automatically.

Additional Considerations in U-Turn Modelling #

As there is no direct feature for U-turn in MiTS, we provide this modelling technique guideline as an alternative for our users. Please note that there will be additional considerations that need to be taken into account.

Cross Slope Rate #

• Cross slope rate setting needs to be carefully observed as the default cross slope rate is in negative value as the road entity starts to slope down from the centerline. Referring to our U-turn sample file above, since we set the centerline to be in between the carriageway (for each left and right lane), we need to set the cross slope rate to be positive for one of the sides.

• Example can be referred below where for road1 (Superelevation > Spread Input > Change Cross Slope Rate), we set the Cross Slope Rate for RHS to be positive value to ensure the carriageways have the correct orientation.

• If the cross section view is observed (Output > Single View > Click on dropdown), you will find that the two carriageways will only slant on one side instead of having a crown at the center.

• However, the cross slope rate setting will still depend on your road design and how you assign the centerline.

Cross Section View #

• Another element that needs to be considered is regarding the cross section view. As we separate the roads to be different, the Cross Section View Output in the road module will also be separated for each of the roads.

• If you go to Output > Single View > Click dropdown, you will see the listed roads which indicate that they are separated.

• However, you may still view the complete cross section by referring to the earthwork module cut section view. What you can do is once the design is completed, proceed to Generate Platform and Slope. Then, create individual cut sections across the roads to view the cut section (Individual > Create Cut Section > Select the Cut Section > Right click on mouse > View Cut Section).

• Below is the example cut section view output from the earthwork.

• If you cannot view the pavement thickness in the cut section view, you may change the setting at the Options > Project Settings > Expand Earthworks > Expand Detailing > Expand Cut Section > Click Table > Include Earthwork by ticking the box > Click OK.