Tracking for the ATLAS level 1 trigger for the high luminosity LHC

At the HL-LHC, the increased luminosity will result in up to 200 pile-up interactions per bunch crossing. One of the greatest challenges for ATLAS will be to keep the Level-1 Trigger \pt\ thresholds low enough in order to keep high trigger efficiency for all the interesting physics. The proposed two-stage design of the ATLAS Level-1 Trigger, and how a Level-1 track trigger fits in this design is described. The requirements and implications for the tracker readout architecture, and estimates of readout bandwidth and latency based on a detailed discrete event simulation of the data flow on the tracker front-end electronics are also presented.