How to solve the invalid arc angle message

Table of Contents

Sometimes in road design, user may face an error prompt on ‘invalid arc angle’ as per image below;

This error occur may due to several possibilities where the data cannot be compute mathematically.

Solution #

Therefore, they are few suggestions to overcome this issue;

a. Change the spiral length to 0 m

b. Reduce the design speed

c. Reduce the design radius

Please go to Horizontal Alignment >> Curve >> Spread Input

As per image attached above, you can see that, you can change the spiral length, design speed and design radius.

As you can see that spiral length for IP 1 is changed to 0 m for both in and out. Now you can proceed to road width

As image above, you can see that the Design Radius is changed to 90 and now you can proceed to road width
Any increase in the radius of the curve beyond this minimum radius will allow you to reduce the side-friction factor, the superelevation rate, or both.

The above image shows that you may change the design speed to allow for the arc angle to be valid and proceed to road width

Furthermore, the design speed, design radius and spiral length is interrelated with each other to calculate the arc angle.

You may refer table below for guideline;