In most American cities, four-way intersections with stoplights are the most common form of traffic control.
As a pedestrian, these intersections are frustrating: if the stoplights are not synchronized, you’ll randomly encounter red lights while walking from block to block. But even when lights are synchronized, they are synchronized for car driving speeds. Thus, at normal walking speed, a pedestrian will inevitably spend a large fraction of travel time waiting at crosswalks for the light to turn green.
Although a pedestrian can increase or decrease their walking speed, it is difficult to select an optimal speed without knowing exactly when the light will change.
Fortunately, a phone app can easily measure walking speed and distance to the next traffic light, and then display a recommended walking speed that will get a pedestrian to the light when it is green (Figure 1).
Using this app, a person can enjoy both a more leisurely pace at lights they’d miss anyway, and can walk ever-so-slightly faster (Figure 2) in order to make it through intersections just before the light turns red.
This type of app would probably work for drivers and bicyclists as well (ideally through audio instructions).
PROS: Encourages walking in cities, thus improving national cardiovascular fitness.
CONS: Users of this app might wait at fewer lights, but would be at higher risk of being run over by a car / bicyclist / steamroller while distracted by the app’s various recommendations and statistics.