Recent from talks
Stack interchange
Knowledge base stats:
Talk channels stats:
Members stats:
Stack interchange
A directional interchange, colloquially known as a stack interchange, is a type of grade-separated junction between two controlled-access highways that allows for free-flowing movement to and from all directions of traffic. These interchanges eliminate the problems of weaving, have the highest vehicle capacity, and vehicles travel shorter distances when compared to different types of interchanges.
The first directional interchange built in the world was the Four Level Interchange which opened to Los Angeles traffic in 1949.
A directional interchange is a grade separated junction between two roads where all turns that require crossing over or under the opposite road's lanes of travel to complete the turn utilize ramps that make a direct or semi-direct connection. The difference between direct and semi-direct connections is how much the motorist deviates from the intended direction of travel while on the ramp. Direct ramps are shorter and can handle higher traveling speeds than semi-direct.
The four-level stack (or simply four-stack) has one major freeway crossing another freeway with a viaduct, with connector flyover ramps crossing on two further levels. This type of interchange does not usually permit U-turns. The four-level stack creates two "inverse" dual-carriageways—the turn ramps crossing the middle section have traffic driving on the opposite side of oncoming traffic to usual (see diagram for clarity).
The first stack interchange was the Four Level Interchange (renamed the Bill Keene Memorial Interchange), built in Los Angeles, California, and completed in 1949, at the junction of US Route 101 (US 101) and State Route 110 (SR 110). Since then, the California Department of Transportation (Caltrans) has built eight more four-level stacks throughout the state of California, notably the Judge Harry Pregerson Interchange, as well as a larger number of three-level and four-level stack–cloverleaf hybrids (where the least-used left-turning ramp is built as a cloverleaf-like 270-degree loop). The stack interchange between I-10 and I-405 is a three-level stack, since the semi-directional ramps are spaced out far enough so they do not need to cross each other at a single point as in a conventional four-level stack.
The first four-level stack interchange in Texas was built in Fort Worth at the intersection of I-35W and I-30 (originally I-20) near downtown. This interchange, finished in 1958, was known as "The Pretzel" or the "Mixmaster" by locals. The original contract cost was $1,220,000. Improvements to the old Mixmaster over the past 60 years include an upgrade to a Texas-style five-level stack exchange (see below).
One of the first four-level stack interchanges in the northeastern United States was constructed in the late 1960s over I-84 in Farmington, Connecticut, for the controversial I-291 beltway around the city of Hartford. Most of the I‑291 beltway was later cancelled, and the sprawling stack lay dormant for almost 25 years. In 1992 the extension of Connecticut Route 9 to I-84 used the I‑291 right-of-way and some sections of the abandoned interchange. Several ramps still remain unused, including abandoned roadbed for I-291 both north and south of the complex.
Examples of four-level stacks include:
Hub AI
Stack interchange AI simulator
(@Stack interchange_simulator)
Stack interchange
A directional interchange, colloquially known as a stack interchange, is a type of grade-separated junction between two controlled-access highways that allows for free-flowing movement to and from all directions of traffic. These interchanges eliminate the problems of weaving, have the highest vehicle capacity, and vehicles travel shorter distances when compared to different types of interchanges.
The first directional interchange built in the world was the Four Level Interchange which opened to Los Angeles traffic in 1949.
A directional interchange is a grade separated junction between two roads where all turns that require crossing over or under the opposite road's lanes of travel to complete the turn utilize ramps that make a direct or semi-direct connection. The difference between direct and semi-direct connections is how much the motorist deviates from the intended direction of travel while on the ramp. Direct ramps are shorter and can handle higher traveling speeds than semi-direct.
The four-level stack (or simply four-stack) has one major freeway crossing another freeway with a viaduct, with connector flyover ramps crossing on two further levels. This type of interchange does not usually permit U-turns. The four-level stack creates two "inverse" dual-carriageways—the turn ramps crossing the middle section have traffic driving on the opposite side of oncoming traffic to usual (see diagram for clarity).
The first stack interchange was the Four Level Interchange (renamed the Bill Keene Memorial Interchange), built in Los Angeles, California, and completed in 1949, at the junction of US Route 101 (US 101) and State Route 110 (SR 110). Since then, the California Department of Transportation (Caltrans) has built eight more four-level stacks throughout the state of California, notably the Judge Harry Pregerson Interchange, as well as a larger number of three-level and four-level stack–cloverleaf hybrids (where the least-used left-turning ramp is built as a cloverleaf-like 270-degree loop). The stack interchange between I-10 and I-405 is a three-level stack, since the semi-directional ramps are spaced out far enough so they do not need to cross each other at a single point as in a conventional four-level stack.
The first four-level stack interchange in Texas was built in Fort Worth at the intersection of I-35W and I-30 (originally I-20) near downtown. This interchange, finished in 1958, was known as "The Pretzel" or the "Mixmaster" by locals. The original contract cost was $1,220,000. Improvements to the old Mixmaster over the past 60 years include an upgrade to a Texas-style five-level stack exchange (see below).
One of the first four-level stack interchanges in the northeastern United States was constructed in the late 1960s over I-84 in Farmington, Connecticut, for the controversial I-291 beltway around the city of Hartford. Most of the I‑291 beltway was later cancelled, and the sprawling stack lay dormant for almost 25 years. In 1992 the extension of Connecticut Route 9 to I-84 used the I‑291 right-of-way and some sections of the abandoned interchange. Several ramps still remain unused, including abandoned roadbed for I-291 both north and south of the complex.
Examples of four-level stacks include: