How do I load Trinity spinoff of ARCOSA

Your info appears to be in error.  
https://www.businesswire.com/news/home/20181101005084/en/Trinity-Industries-Announces-Completion-Spi...
That indicates you would receive 1 ACA share for every 3 TRN shares held on 10/17/18

If you had on 10/17/18 30 shares of Trinity, you would be receiving 10 shares of Arcosa.  The share ratio is 0.333333.  In Quicken, that will likely produce an Add Shares transaction for 9.99999 shares.  You will need to edit that transaction to read as 10 shares.  

Yahoo finance tells me TRN closed on 11/1 at 22.72.  It does not provide data for ACA until 11/5 for some reason.  Those prices (fair market values) for TRN and ACA are mondatory for Quicken to properly allocate cost basis between the two companies.  I would defer on entering that transaction into Quicken until they issue the Form 8937 for this transaction.  That could take 5 days to 6 weeks.  (It may already be out.  I didn't look.)

Richard Edelen said:

Thanks, Quicken generates 3 entries, should I delete the other 2?

What Quicken generates would depend on your specific holdings.  Three transactions would be the minimum -- a Remove Shares of TRN removing 30 shares, and Add Shares for TRN adding back the 30 shares with a reduced cost basis, and an Add Shares for ACA adding in 10 shares with its applicable cost basis.  None of those should be deleted.   Indeed, off the top, I can't think of a reason to delete any of the transactions Quicken would have generated through the Corporate Spinoff action.  

If you are saying through a download of transactions from your brokerage you got new transactions, that is a totally different question.  Those transactions may be suspect, but there is not enough information to give you advice.