Driving at a constant speed, Reggie travels 300 kilometers in 1 hour.

To find Reggie’s speed in kilometers per hour, you can use the formula:

\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \]

In this case, the distance is 300 kilometers and the time is 1 hour. Plugging in the values:

\[ \text{Speed} = \frac{300 \text{ km}}{1 \text{ hour}} = 300 \text{ km/h} \]

Reggie drives at a speed of 300 kilometers per hour.