Two-Lane Highways
Two-lane highways, which have one lane per direction, are unique operationally, since they may allow passing through the use of the opposing traffic stream. According to the US Federal Highway Administration [1], two-lane highway facilities represent abou
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Two-Lane Highways
Two-lane highways, which have one lane per direction, are unique operationally, since they may allow passing through the use of the opposing traffic stream. According to the US Federal Highway Administration [1], two-lane highway facilities represent about 97 % of the total highway system and for more than 65 % of the total nonurban vehicular travel in the USA. Hence, two-lane highways provide most of the primary interurban highway network as well as being the basis of the secondary highway and collector networks. Figure 11.1 provides a sketch of a two-lane highway. When passing zones are provided, they are marked using dashed lines between the two opposing traffic streams, and vehicles following a slower vehicle must evaluate the gaps in the opposing direction before deciding whether to pass. Thus, around passing zones, the capacity and operations of one direction depend on the demand in the other direction. For segments with no-passing zones, vehicles must follow the lead vehicle in a platoon. Facilities with no-passing opportunities increase the probability of car-following (formation of platoons) and reduce the ability of drivers to travel at their desired speeds. Therefore, one important performance measure that has been used to evaluate two-lane highways is the percent time spent following (PTSF). Two-lane highways are often designed with passing lanes, which are additional lanes provided at selected locations throughout the length of the facility to provide passing opportunities. A climbing lane is a passing lane added along an upgrade section to allow traffic to pass heavier and slower vehicles. In Europe (e.g., Finland and Sweden), there are two-lane highways designed with wider cross sections at selected locations intended to provide passing opportunities without providing an additional lane; at those facilities, vehicles use part of the opposing lane to pass. Other features used along two-lane highways are turnouts and two-way left-turn lanes. Turnouts are shoulder areas designed to allow vehicles to pull off in order to allow faster vehicles to pass. Two-way left-turn lanes are additional lanes provided between the two directions to allow left-turning vehicles to access driveways and intersections along the facility without obstructing through traffic.
L. Elefteriadou, An Introduction to Traffic Flow Theory, Springer Optimization and Its Applications 84, DOI 10.1007/978-1-4614-8435-6_11, © Springer Science+Business Media New York 2014
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Two-Lane Highways
Fig. 11.1 Sketch of a two-lane highway
Fig. 11.2 Passing maneuver along a two-lane highway
This chapter first discusses the operation of two-lane highways and then provides an overview of capacity estimation for these facilities. The third section discusses the HCM 2010 analysis procedures for two-lane highways, while the last section provides an overview of microsimulation tools available to evaluate their operation.
Principles of Two-Lane Highways Operations To understand traffic operations along two-lane highways
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