Available with Standard or Advanced license.
The Proportion command 
on the COGO toolbar splits a selected line feature into a number of segments, based on specified distance values. If there is a difference between the feature length and the entered values, this difference is proportioned between all the new segments. Proportion is useful when you are working with exact measurements, such as COGO or survey data.
For example, you have line features that need to be split into specific lengths. The example below shows a line feature that needs to be split into four parts: 13.79 feet, 48 feet, 60 feet, and 60 feet. The Proportion command is used to split this feature into the four new features. 
The lengths you entered add to 181.79 feet. If the length of the input feature is either longer or shorter than this value, the difference is proportioned among the new features. So if the length of the original feature were 182 feet, it is to be proportioned into features that are as follows: 13.807 feet, 48.055 feet, 60.069 feet, and 60.069 feet long.
- Click the Edit tool
on the Editor toolbar and click the feature.
- Click Proportion on the COGO toolbar.
- The direction of the selected line is indicated by arrows on the map. Choose which end to start proportioning by clicking either from the start point or the endpoint of the line.
- Click the label <Click To Enter Length>, type the distance value, then press ENTER to add the length. The Proportioned column shows the GIS length of the feature that will be created. Proportioned Value = (Length / Entered Length) * Feature Length.
- Continue to add lengths until you are done. Press ESC once to get out of enter mode.
- To modify an existing length, either double-click to edit it or press the SPACEBAR while it is highlighted.
- To move a length up or down the list, highlight it and hold down CTRL and press the up or down arrow keys, or click the Move Up or Move Down buttons.
- To remove a length from the list, highlight it and press the DELETE key, or click the Delete button.
- To duplicate and reenter a highlighted length, press ALT+D or click the Duplicate button to open the Proportion - Duplicate dialog box.
- Click OK when you are done entering lengths.
The line is split proportionally to the length of the measured segments. Any difference between the line length and the sum of the length of the segments is allocated proportionately to the new line's length. If your line feature has COGO fields and valid COGO attributes, the length you entered will be updated for each output feature.