CVE 06 Highway And Railroad Engineering Module 11 PDF

Republic of the Philippines SOUTHERN LUZON STATE UNIVERSITY College of Engineering Civil Engineering Department Lucban, Quezon CVE 06 HIGHWAY AND RAILROAD ENGINEERING...

Republic of the Philippines SOUTHERN LUZON STATE UNIVERSITY College of Engineering Civil Engineering Department Lucban, Quezon CVE 06 HIGHWAY AND RAILROAD ENGINEERING Module No. 11 GRADE SEPARATIONS AND INTERCHANGES The ability to accommodate high volumes of traffic safely and efficiently through intersections depends largely on the arrangements provided for handling intersecting traffic. The greatest efficiency, safety, and capacity are attained when the intersecting traveled ways are grade separated. An interchange is 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. Factors in selecting appropriate type of grade separation and interchange - highway classification - character and composition of traffic - design speed - degree of access control - economics - terrain - right-of-way To avoid conflicts between vehicles, pedestrians, and/or bicycles within interchanges, it is preferable to separate their movements. When separation cannot be provided, each interchange site should be studied and alternate designs considered to determine the most appropriate arrangement of structures and ramps to accommodate bicycle and pedestrian traffic through the interchange area. WARRANTS FOR INTERCHANGES AND GRADE SEPARATIONS The following six conditions, or warrants, should be considered when determining if an interchange is justified at a particular site: 1. Design designation. The determination to develop a highway with full control of access between selected terminals becomes the warrant for providing highway grade separations or interchanges for all intersecting roadways crossing the highway. 2. Reduction of bottlenecks or spot congestion. Insufficient capacity at the intersection of heavily traveled routes results in intolerable congestion on one or all approaches. Inability to provide essential capacity with an at-grade facility provides a warrant for an interchange where development and available right-of-way permit. 3. Safety improvement. Some at-grade intersections have a disproportionate rate of serious crashes. If inexpensive methods of eliminating crashes are likely to be ineffective or impractical, a highway grade separation or interchange may be warranted. CVE 06 HRE 11 118 JCSaliendra 4. Site topography. At some sites, grade-separation designs are the only type of intersection that can be constructed economically. The topography at the site may be such that, to satisfy appropriate design criteria, any other type of intersection is physically impossible to develop or is equal to or greater than the cost of a grade- separated design. 5. Road-user benefits. The road-user costs due to delays at congested at-grade intersections are large. Road-user costs, such as fuel and oil usage, wear on tires, repairs, delay to motorists, and crashes that result from speed changes, stops, and waiting, are well in excess of those for intersections permitting uninterrupted or continuous operation. In general, interchanges involve somewhat more total travel distance than direct crossings at grade, but the added cost of the extra travel distance is less than the cost savings resulting from the reduction in stopping and delay. The relation of road-user benefits to the cost of improvement indicates an economic warrant for that improvement. 6. Traffic volume warrant. Volumes in excess of the capacity of an at-grade intersection would certainly be a warrant. Interchanges are desirable at cross streets with heavy traffic volumes because the elimination of conflicts due to high crossing volume greatly improves the movement of traffic. Not all warrants for grade separations are included in the warrants for interchanges. Additional warrants for grade separations include grade separations that would: → Serve local roads or streets that cannot practically be terminated outside the right- of-way limits of freeways. → Provide access to areas not served by frontage roads or other means of access. → Eliminate a railroad-highway grade crossing. → Serve unusual concentrations of pedestrian traffic (for instance, a city park developed on both sides of a major arterial). → Serve bikeways and routine pedestrian crossings. → Provide access to mass transit stations within the confines of a major arterial. → Assure free-flow operation of certain ramp configurations and serve as part of an interchange. Interchange Configurations CVE 06 HRE 11 119 JCSaliendra  Interchange Configurations Typical Grade Separation Structures With Closed Abutments CVE 06 HRE 11 120 JCSaliendra  Typical Grade Separation Structure With Open-End Span Two Variations Of Roadways Crossing At Three Or Four Levels Overpass Roadways Typical Overpass Structures CVE 06 HRE 11 121 JCSaliendra  Typical Overpass Structures INTERCHANGES Three-Leg Designs An interchange with three intersecting legs consists of one or more highway grade separations and one-way roadways for all traffic movements. When two of the three intersection legs form a through road and the angle of intersection is not acute, the term T interchange applies. When all three intersection legs have a through character or the intersection angle with the third intersection leg is small, the interchange may be considered a Y configuration. A clear distinction between the T and Y configurations is not important. Regardless of the intersection angle and through-road character, any basic interchange pattern may apply for a wide variety of conditions. Three-leg interchanges should only be considered when future expansion to the unused quadrant is either impossible or highly unlikely. This is due in part to the fact that three-leg interchanges are very difficult to expand or modify in the future. Three-Leg Interchages With Single Structures CVE 06 HRE 11 122 JCSaliendra  Three-Leg Interchages With Multiple Structures Three-Leg Interchange (T-Type Or Trumpet) CVE 06 HRE 11 123 JCSaliendra  Three-Leg Interchange Semidirectional Design Directional Three-Leg Interchange Of a River Crossing Trumpet Freeway-To-Freeway Interchange CVE 06 HRE 11 124 JCSaliendra Four-Leg Designs Interchanges with four intersection legs may be grouped under five general configurations: (1) ramps in one quadrant, (2) diamond interchanges, (3) single- point urban interchanges (SPUIs), (4) full or partial cloverleafs (including ramps in two or three quadrants), and (5) interchanges with direct and semidirect connections. 1. Ramps in One Quadrant Interchanges with ramps in only one quadrant have application for an intersection of roadways with low traffic volumes. Four-Leg Interchanges, Ramps In One Quadrant CVE 06 HRE 11 125 JCSaliendra 2. Diamond Interchanges The simplest and perhaps most common interchange configuration is the diamond. A full diamond interchange is formed when a one-way diagonal ramp is provided in each quadrant. The ramps are aligned with free-flow terminals on the major highway, and the left turns at grade are confined to the crossroad. The diamond interchange has several advantages over a comparable partial cloverleaf: all traffic can enter and leave the major road at relatively high speeds, leftturning maneuvers entail little extra travel, and a relatively narrow band of right-of-way is needed, sometimes no more than that needed for the highway alone. Diamond Interchanges, Conventional Arrangements CVE 06 HRE 11 126 JCSaliendra  Diamond Interchange Arrangements To Reduce Traffic Conflicts Freeway With A Three-Level Diamond Interchange CVE 06 HRE 11 127 JCSaliendra  Diamond Interchanges With Additional Structures Existing Four-Leg Interchange With Diamond Stage Construction CVE 06 HRE 11 128 JCSaliendra 3. Single-Point Urban Interchanges The single-point urban interchange (SPUI) is a relatively recent development in interchange design with the first SPUIs being constructed in the early 1970s. The SPUI is also known as an urban interchange or a single-point diamond interchange. The primary features of a SPUI are that all four turning moves are controlled by a single traffic signal and opposing left turns operate to the left of each other. Underpass Single Point Urban Interchange An SPUI Underpass in Restricted Right-of-Way CVE 06 HRE 11 129 JCSaliendra  Overpass Layout With a Frontage Road And a Separate u-Turn Movement CVE 06 HRE 11 130 JCSaliendra  Underpass SPUI Overpass SPUI 4. Cloverleafs Cloverleafs are four-leg interchanges that employ loop ramps to accommodate left- turning movements. Interchanges with loops in all four quadrants are referred to as “full cloverleafs” and all others are referred to as “partial cloverleafs.” Four-Leg Interchange, Full Cloverleaf With Collector-Distributor Rods CVE 06 HRE 11 131 JCSaliendra  Cloverleaf Interchange With Collector-Distributor Roads Schematic Of Partial Cloverleaf Ramp Arrangements, Exit And Entrance Turns Four-Leg Interchange (Partial Or Two-Quadrant Cloverleaf With Ramps Before Main Structure) CVE 06 HRE 11 132 JCSaliendra  Four-Leg Interchange (Partial Or Two-Quadrant Cloverleaf With Ramps Beyond Main Structure) 5. Directional and Semidirectional Interchanges Direct or semidirect connections are used for important turning movements to reduce travel distance, increase speed and capacity, eliminate weaving, and avoid the need for out-of-direction travel in driving on a loop. Higher levels of service can be realized on direct connections and, in some instances, on semidirect ramps because of relatively high speeds and the likelihood of better terminal design. Often a direct connection is designed with two lanes. In such cases, the ramp capacity may approach the capacity of an equivalent number of lanes on the through highway. Semidirect Interchange With Weaving CVE 06 HRE 11 133 JCSaliendra  Semi Direct Interchange With No Weaving Semidirectional And Directional Interchange - Multilevel Structures CVE 06 HRE 11 134 JCSaliendra  Directional Interchange, Two Semidirect Connections Four-Level Directional Interchange Four-Level Directional Interchange CVE 06 HRE 11 135 JCSaliendra  Semidirectional Interchange With Loops OTHER INTERCHANGE CONFIGURATION Offset Interchange Via Ramp Highway Four-Leg Interchange, Diamond With A Semidirect Connection CVE 06 HRE 11 136 JCSaliendra  Four-Leg Interchange, Cloverleaf With A Semidirect Connection Complex Interchange Arrangement Freeway With A Three-Level Cloverleaf Interchange Reference: American Association Of State Highway And Transportation Officials (AASHTO), A Policy Of Geometric Design Of Highways And Streets CVE 06 HRE 11 137 JCSaliendra