Intersections

Types of Intersections

Uncontrolled intersections are junctions without signs or traffic signals. Right-of-way belongs to the vehicle on the main road in three-way intersections, to the vehicle on the right in four-way intersections. Controlled intersections are marked by signals, traffic signs, or roundabouts. Despite the clarity of rules of the road governing controlled intersections, more accidents occur at these sites. According to a report from the National Highway Traffic Safety Administration (NHTSA), in an estimated 787,236 intersection-related crashes in 2008, about 52.5 percent (413,140) that were assigned a critical reason were traveling on roadways that were controlled by at least one traffic signal and 31.3 percent (246,385) by at least one stop sign.

The higher volume of traffic at controlled intersections is doubtless a contributing factor, but so is the number of drivers who are reckless or distracted. One study found that two of five drivers admitted to having run a red light within the past 30 days, and the 2008 NHTSA report found that in 96.1 percent of crashes the critical reasons were attributed to drivers. This includes 55.7 percent (438,194) drivers with recognition error (inattention, internal and external distractions, inadequate surveillance, etc.) and 29.2 percent (230,047) with decision errors (too fast for conditions or aggressive driving, false assumption of other's actions, illegal maneuver, and misjudgment of gap or other's speed).

Controlled intersections can present hazards for pedestrians and bicyclists too. Six percent of urban bicycle–motor vehicle collisions are related to these users not being able to finish crossing an intersection before the opposing traffic is released. Pedestrians—particularly children, the elderly, and the disabled—may also find it difficult to cross in the allotted time. The 2009 National Manual on Uniform Traffic Devices proposed a reduction from 4 feet per second, a common crossing time, to 2.8 feet per second.

Based on road design, the most common type of intersection is the four-way intersection where two roads cross. T-intersections occur when one road dead-ends into a through road. Generally, the minor road at a T-intersection is controlled by a stop sign that directs the driver to wait until the major road is clear before proceeding. A Y-intersection also has three legs, often appearing as if two roadways merge to form one. Such roads may be marked with stop signs on all roads. Occasionally, an intersection has five or more intersecting roads. A six-way intersection involves the crossing of three streets, most often two perpendicular streets and a diagonal street. More than six roads intersecting is rare. A roundabout is an intersection that merges traffic from multiple roadways into a circle. In the United States, traffic moves counterclockwise.

...