calculate mean based on line length

[SarahHartholt]

Hi everyone,

I'm wondering if it is possible to join/merge line segments based on a common ID field and calculate the average of one of the other fields using the line segment length. 

For example, in the following graphic I want to join the line segments that fall within the polygon outlined in turquois. The yellow segment is 100m long and has a value of 50% and the orange segment is 200m long and has a value of 20%. What sort of workflow could I used to calculate the new value?

[DanPatterson]

Dissolve is what you are describing

Dissolve (Data Management)—ArcGIS Pro | Documentation

but if you only want to include the portions within the polygons, you will have to Clip first