Insert into table from a query to a linked database hangs
Based on your question and other discussion comments, I didn't see any clue for network and blocking issues.

Here, I'd like to give following approaches to try which can help in your situation:

Approach#1:

Suspecting performance issue because of indexes in STG_TRANSIT table. In the sutuation of big STG_TRANSIT table
and there are indexes available, what if you might drop them and rebuild them after populating tables during off hours.

Approach#2:

Create temporary table - 

create table temp_STG_TRANSIT 
as
select * from 
(
  SELECT TRIM(r.R_ID), 1, TRIM(r.R_CODE), TRIM(r.R_MISC4), trim(rc.DESCR)
  FROM sradmin.RACEWAY@sr25 r
  LEFT JOIN sradmin.RWAYCODE@sr25 rc ON r.R_CODE = rc.R_CODE
)
Where Rownum &lt;= 10000;


Perform bulk insert -

insert /* APPEND */ into STG_TRANSIT select a.* from temp_STG_TRANSIT as a;


Approach#3:

Trying with DRIVING_SITE hint which forces query execution to be done at a different site than the initiating instance, following query pattern can help in your context:

INSERT INTO STG_TRANSIT(TRANSIT_ID, SHIP, TRANSIT_TYPE, COMPARTMENT_ID, DESCRIPTION)
SELECT /*+ DRIVING_SITE(X) */ *
FROM
(
    SELECT TRIM(r.R_ID), 1, TRIM(r.R_CODE), TRIM(r.R_MISC4), trim(rc.DESCR)
    FROM sradmin.RACEWAY@sr25 r
    LEFT JOIN sradmin.RWAYCODE@sr25 rc ON r.R_CODE = rc.R_CODE
) X


Refer link for the details of DRIVING_SITE hint.