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Four Lane Highways

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On four lane highways traffic flows in opposite directions on each pair of lanes, and passing is accomplished within the lanes of forward movement of traffic and not in the lanes of opposing traffic. The amount of interaction between opposing traffic flows is substantially reduced, except in the case of left turning vehicles. A feeling of freedom from from opposing traffic generally results in smoother operation and an increase in the capacity per lane over that of two and three lane highways. Four lane highways provide at least four times the capacity of a two lane highway for the same assumed design speed.


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Although the four lane highway is the basic multilane type, traffic volume sometimes warrants the use of highways with six, eight, or more lanes, particularly in highly developed urban areas. Eight lane highways, with four lanes in each direction, are typically the upper limit for multilane highways due to a variety of problems related to multiple lane changes, which adversely affect capacity and safety. If more than four directional travel lanes are required, channelization, frontage roads, or other directional traffic flow measures are often added to the highway to improve the efficiency and traffic handling capacity of the facility.



Highway and Transport Engineering
and this section is about Four Lane Highways
(refference : Wright, P.H, with contributions by James S. Lai, Peter S.Parsonson, Michael Meyer., Highway Engineering, 6th edition ,John Wiley & Sons, Inc.New York, 1996.)

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