Highway contains a number of roads connected with each other. Ramps connect two and more than two roads with each other on a highway. When a road passes over the other roads and connects to each other with the ramps it creates an interchange. An interchange can have more than one ramps and junctions for traffic stream. Basically, interchange allows the traffic to flow on a single highway and road junction without going towards any other traffic stream.
Interchanges existence is necessary for roads that face sometimes overload and huge traffic. Interchanges are also the requirement of the road in case of the limited access divided highway. In the transportation system, building a grade separation at interchanges is quite normal from the very past. However, it was adopted for the trains in the 17th century prior than the road transportation system.
Basically, interchanges provide the solution to the problem of road’s capacity for the traffic. Various factors influence the configuration of the particular site as the traffic load, truck traffic, signs, intersecting legs, and topography of the site.
Major Types of Interchange
There are various types of interchanges configuration. At the grade separation transportation turning movements are controlled and accommodated through the configuration of various interchanges. Some interchanges in the world have created an alternative for other basic types of interchanges because of poor experiences of design. Safety, politics, development of site, environment, and cost are the factors that vary in all interchanges. Purpose of development and functions of the interchanges create difference and categorizes the interchanges in various categories. In this paper comparison between the interchanges is presented. However, categorization is based on the access of interchanges to the relevant road facilities.
Services interchanges work as an interchange for the traffic to connect a freeway at the side of highways in the rural and urban areas. In Pakistan, there are a number of interchanges established at the highways in various forms like partial cloverleaf, and roundabouts. However, cloverleaf interchange form is more common as compared to other forms in the Pakistan. In other countries, cloverleaf interchanges form is also in use for the expected free flow at interchanges of freeways aligned with primary highways.
Diamonds interchange contain four ramps for traffic. In such interchanges, traffic gets entrance and goes out to the freeway with a small right angle towards the highway. Traffic signs and signals control the traffic going and coming from ramps at the highway. Diamond interchanges are cost effective however becomes more risky for accidents in case of the increase in traffic.
Cloverleaf is a complex designed form of interchange with four ways and two levels. In cloverleaf loop ramps works for all left turns. In case a vehicle wants to go towards the left side, it will first cover the targeted track and then it will get entrance in the 270 degrees sharp and curved loop ramp. Weaving is the current shortcoming of this type of interchanges. Cloverleaf also require less financial and material resources at the time of construction as it is limited to only one bridge construction. Therefore cloverleaf is also considered as a cost effective junction.
Partial cloverleaf a modification of the cloverleaf is based on 4-6 ramps. According to the design, two ramps from these connects to the highway as loop ramps. Partial cloverleaf is relatively safer than the complex cloverleaf. Land required for the partial cloverleaf depends upon the total number of ramps that will be built in interchange. Partial cloverleaf is inexpensive in regards to construction expense. Increases in the number of ramps increase the overall capacity and efficiency of the interchange.
Partial clover having two quadrants and four number of ramps is also famous as folded diamond. Cloverleaf can be easily converted to the partial cloverleaf if there is no link with the highway. However, it reduces the capacity and eliminate the weaving but increase safety for the traffic.
In the European countries roundabout usually have about three levels the below, above and middle level of two different highways. The roundabout is also an alternative for the interchanges at the highway and freeways. In roundabouts interchanges constructed at the highways, ramps rotary on three different levels. Roundabouts usually require the only construction of three bridges. Therefore in regards to the material and land consumed during roundabout construction cost usually incur less than the other type of interchanges. While on the other hand, roundabouts have limited capacity that is less than the other interchanges. Therefore roundabouts generate traffic problems when the heavy flow of traffic comes to the roundabouts.
Interchanges constructed between two freeways is named as system interchange. System interchanges work as the directional interchange with one to three cloverleaf or loops. System interchanges provide direction to the traffic through the loops constructed in various directions. System interchanges face problems with the heavy traffic, therefore, its operational performance gets effects in the urban regions. Other than that, in various areas of the urban regions right of way requirements of system interchanges are also ignored.