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An interchange is defined as a system of interconnecting roadways in conjunction with one or more grade separations that provides for the movement of traffic between two or more roadways or highways on different levels. Interchanges are utilized on freeways and expressways, where access control is important. They are used on other types of facilities only where crossing and turning traffic cannot be accommodated by a normal at-grade intersection.

Interchange Spacing. Interchanges should be located close enough together to properly discharge and receive traffic from other highways or streets, and far enough apart to permit the free flow and safety of traffic on the main facility. In general, more frequent interchange spacing is permitted in urbanized areas...

A two-way left turn lane may be considered a special type of “intersection” design, since its purpose is to provide a separate lane for traffic in both opposing lanes to slow down and turn out of the traffic stream in front of opposing traffic. Rather than concentrate the left turners at a single crossroad intersection, the two-way left turn lane spreads out the turning movements over a continuous stretch of roadway. Mid-block left turns are often a serious problem in urban and suburban areas. They can be a safety problem due to angle accidents with opposing traffic as well as rear-end accidents with traffic in the same direction. Mid­block left turns also restrict capacity. Two-way left turn lanes (TWLTLs) have proven to be a safe and cost-effective solution to this problem...

At-grade intersections should be designed to promote the safe movement of traffic on all legs with a minimal amount of delay to drivers using the intersection. The amount of delay a driver experiences is the measure of effectiveness for signalized intersections as used in capacity analysis. Factors to be considered in designing an intersection are:

• Traffic volumes on all legs, including separate counts for turning vehicles

• Sight distance

• Traffic control devices

• Horizontal alignment

• Vertical alignment

• Radius returns

• Drainage design

• Islands

• Left turn lanes

• Right turn lanes

• Additional through lanes

• Recovery areas

• Pedestrians

• Bicycles

• Lighting

• Development of adjacent property

Traffic Volumes...

An intersection is defined as an area where two or more roadways join or cross. Each roadway extending from the intersection is referred to as a leg. The intersection of two roadways has four legs. When one roadway ends at the intersection with another roadway, a three-leg intersection, or T intersection, is formed. Some intersections have more than four legs, but this design should be avoided, since the operation of traffic movements
is usually inefficient...