Coordinated intersections include two or more intersections that promote progression between each other along a corridor. According to the National Association of City Transportation Officials’ (NACTO’s) Urban Street Design Guide, coordinated intersections are typically spaced one-half mile or less apart and provide more continuous traffic flow for major street users going from one coordinated intersection to the next. Coordinated intersections can be optimized to a specific target speed to meet the lower speed needs of bicyclists and pedestrians.

According to the HCM, groups of two or more intersections that are closely spaced and work operationally together using displaced or distributed movements are clustered intersections. It is recommended that these intersection clusters be analyzed as one system. Most alternative intersections are made of clustered intersections due to left-turn or U-turn movements that occur either before or after the main intersection.

In a High-Tee (Unsignalized CGT) or CGT intersection, one major street movement passes through the intersection without stopping. This movement typically occurs on the opposite side of the side street (on top of the “T”). The other major street direction of travel is typically uncontrolled or controlled by a traffic signal. Vehicles turning left from the side street to the major street use a left-turn pocket and merge with the major street through traffic. CGT intersections are not suitable for highspeed roadways (> 55mph). CGT intersections can be difficult for pedestrians to cross. See

Figure 10-3

for the basic features of a CGT.

This alternative intersection can either have traffic signals or be stop controlled. RCUTs have directional medians to force minor street through and left-turning traffic to make a right-turn and then a U-turn on the major street to complete their maneuvers. When analyzing operations or safety of an RCUT intersection, the analysis typically includes the core intersection as well as the satellite intersections. See

Figure 10-4

for the basic features of an RCUT intersection.

At MUT intersections, left-turning traffic on the major and minor street U-turn at wide medians to complete their maneuver. This eliminates the need for left turn phases at the intersection. When analyzing operations or safety of a MUT intersection, the analysis typically includes the core intersection as well as the travel time and delay at the satellite intersections. See

Figure 10-5

for the basic features of a MUT intersection.

Also known as a continuous flow interchange (CFI) or crossover displaced left-turn (XDLT), this signalized intersection type relocates one or more left-turn movements on an approach to the other side of the opposing traffic flow. Signals are placed at crossover intersections upstream of the main intersection and left-turn movements run simultaneously with the through movement, eliminating the need for a left-turn phase for that approach. When analyzing operations or safety of a DLT intersection, the analysis typically includes the core intersection as well as the satellite intersections. See

Figure 10-6

for the basic features and flow patterns of a DLT. This intersection type requires restriction of access within the influence area of the layout. Right-in and right-right access may be permitted but not close to the cross-over areas

TWSC intersections are comprised of one uncontrolled street and one stop-controlled street (see

Figure 10-7

). A typical configuration of TWSC intersections is a four-leg intersection with an uncontrolled major street and a stopcontrolled minor street. Another typical configuration is a three-leg intersection where the third leg (minor street) is stop-controlled, and the major street is uncontrolled. TWSC are typically applied at locations with a large majority of overall intersection traffic occurring on the major street. Safety analysis of TWSC intersections is discussed in

Section 10.3

of this chapter or in

Chapter 5

and

Chapter 6

.

At AWSC intersections, all approaches have stop control (see

Figure 10-8

). AWSC are typically applied at locations with a balanced volume of vehicles traveling on intersecting segments. Operational analysis of AWSC intersections is dependent on traffic patterns at the intersection because delay at each approach is dependent on the arrival patterns of the other approaches. Safety analysis of Two-way Stop-controlled intersections is discussed later in this chapter and in

Chapter 5

and

Chapter 6

.

Roundabouts are circular intersections that use either signals or yield control and channelizing islands to circulate traffic in a counterclockwise motion around and through an intersection. The channelizing islands provide a refuge for pedestrians. The geometric features of a roundabout deflect and slow approaching vehicles. Roundabouts are designed to varying sizes from a single-lane mini-roundabout with a 90-foot inscribed circle diameter to a multi-lane roundabout with a 200-foot inscribed circle diameter. An

example

of a roundabout is shown in

Figure 10-9

. For more information about roundabouts (including example figures) and roundabout analysis, see

Chapter 12

.

Grade separation is a method of aligning a junction of two or more roadways at different heights (grades) so that they will not disrupt the traffic flow on other routes when they cross each other. Grade separation is typically introduced for the major street through movement, while major street turning movements and all minor street movements still occur at the same grade. See

Figure 10-10

for the basic features of a grade-separated intersection.