A driver sees the low-air warning activate at highway speed but the gauge still shows about 60 psi. What is the safest response?

1. Keep driving because 60 psi is always enough for the rest of the trip
2. Stop promptly in a safe place; the remaining air may be enough for a stop if the driver acts immediately
3. Pump the brakes to build pressure faster
4. Use the hand valve as the main brake and continue