While many developing cities required sidewalks to create a uniform appearance, they were optional from the start in Tucson. There wasn't much need for them because there was little rain, and therefore little need to create a system for runoff. Considering the economic situation at the time, there were few takers. To this day, some streets have a few feet of sidewalk, then a few feet of dirt, and so on. There's little chance of falling asleep at the wheel on Tucson streets.
Drivers have plenty to hold their attention.
On Grant Road and Broadway through the heart of the city, sometimes the center lane is a turn lane. Sometimes it is for westbound traffic only, with no turns allowed. And sometimes it is for eastbound traffic only. Now you know why we call them suicide lanes. The system, used at most lights throughout the area, allows drivers to turn left on a green light, and then gives them some extra time to turn on a green arrow at the end of the cycle.