A delivery truck driver was making deliveries across different cities and initially drove at a speed of 120 kilometers per hour on the highway to meet a strict deadline. However, after entering the city limits with traffic and speed regulations, the driver had to slow down to 54 kilometers per hour for safety and compliance. The company wants to know approximately how many miles per hour the speed was reduced to assess fuel consumption and time management more accurately. (Use 1 kilometer ≈ 0.625 mile)