What is the typical duration for a major street through phase at traffic signals?

Answer: C — 15 to 25 seconds

The typical duration for a major street through phase at traffic signals is commonly set between 15 to 25 seconds. This duration allows enough time for vehicles traveling on the major street to clear the intersection safely without creating excessive delays, especially considering the volume of traffic that major streets typically experience. When timing traffic signals, engineers consider several factors including average vehicle speeds, pedestrian crossing times, and the need to minimize stops for vehicles. The selected time frame ensures that vehicles can pass through without unnecessarily prolonging wait times for traffic on side streets, which typically have shorter phases. In the context of the other options, durations below 15 seconds would likely be insufficient for the volume and speed typically seen on major streets, while durations extending beyond 25 seconds might lead to increased congestion and frustration for drivers, drawing attention to the importance of balancing traffic flow with safety.