Derrick drives 19 miles per hour in traffic. What is his speed in traffic, in kilometers per hour? 1 kilometer = 0.62 miles

To convert miles to kilometers, we can multiply the number of miles by 0.62.

Therefore, Derrick's speed in traffic, in kilometers per hour, is 19 miles/hour * 0.62 kilometers/mile = 11.78 kilometers/hour. Answer: \boxed{11.78}.