How do I combine 3 records into 1 in an attribute table and sum the lengths of those 3 records in the new record

[CourtneyWade]

I am using ArcGIS Pro and I am working with road data where the road is divided into segments. Each segment is listed as individual records in the attribute table. For example, there are 3 records (segments) for RoadNumber 1003. Not only am I wanting to join the 3 segments into 1 record withing the original attribute table, I am also wanting the field ‘seglength’ of the combined record to give the sum of the 3 segments. Is this possible and if so, would you please explain the steps to achieve these resulrts? I greatly appreciate it. 

 This is the screenshot of the table:

This is what I was hoping to do (I'm nor sure what happens in the final two columns)

[DanPatterson_Retired]

You want a Summary... on you LCOMM field with a Sum on the Shape_Length field

[CourtneyWade]

Thank you Dan. I am able to follow your directions, but it makes another feature layer. Is there away to keep the newly combined record replace the original 3 in the original attribute table?

[DanPatterson_Retired]

Most operations produce a new file. You can join the results of the summary table to the original or dump the original.  It is all a matter of what is the most important.  If you want to reduce the size of the bits of the file, you can do a

Dissolve but then you may run into losing attributes

Disk space is cheap, organization is driven by need and what is important