When descending a steep 8% gradient on the Austrian Tauern Autobahn (A10), what is the correct operational strategy for managing the continuous retarder and service brakes?

1. Use the service brakes continuously with light foot pressure to hold a steady speed
2. Select an appropriate transmission gear and modulate the retarder in stages to match the descent speed, keeping friction service brakes cold for emergency stopping
3. Shift the automated transmission into neutral to allow free coasting and save fuel
4. Turn off the engine retarder switch and pump the service brakes rapidly every 3 seconds