Is this correct to say that TRA is a time allowance for risk identified in the RR?
No not realy. TRA is risk that the Contractor has allowed against activities on the programme. The simplest way to show this is is to have a TRA column on your programme showing the proportion of that activity is for risk which is the Contractors under the contract e.g. weather up to 1in10 year event, ground conditions, mechanical breakdown etc. An item 10 days long with 2 days TRA could be done in 8 days if everything goes perfectly but will more than likely take closer to 10 days. If could take longer, so equally is not simply worst case scenario either.
The sole purpose of showing TRA is to give the Employer a bit more comfort that the Contractor’s programme is achievable. It is owned by Contractor so can not be used to absorb CE’s. It is not only the items that are in the Risk Register that need to be considered (and some items on Risk Register will not even be on the programme if they are Employer risks).