DR, Forced DR and Traffic Hos are all used for the same purpose. In some cases the normal HO criterion should be fulfilled else there are some other parameters that specify the minimum Rxlev of the neighbour and the min TS available on the nei cell to allow for such HOs to take place. Please specify your vendor, for Motorola and Alcatel I might be able to help, please specify your vendor. else look for Congestion Relief / Directed Retry in your parameter documentation.
By the way you can also in some vendors set the cells priority to Low thereby it takes calls only if it is the only server else other cells are camped in idle mode. It proves useful for Cells looking in remote with some but not complete overlapping and experiancing congestion. This way you don’t loose coverage and still offload the MS for call setup Traffic.