Abstract

A lane drop is defined as a location on a highway where the number of lanes provided for through traffic decreases. For purposes of this study, the broad category of lane drops has been further subdivided into three specific classes: lane exits, lane splits, and lane terminations. These subdivisions are illustrated schematically in Figure 1. A lane exit refers to a location where the number of through lanes decreases at an interchange on a multilane roadway. A designation of lane split denotes a major fork of a multilane highway where the level of traffic service provided at the terminus of either prong is approximately equal. Thus, the lane split does not have the same exit connotation which is associated with a lane exit. The third category is the lane termination which occurs when a lane is simply terminated. A lane termination leaves a driver with no choice, he must merge into the other available lane(s). A lane termination also has no connection with an exiting situation.

Associated with the first two categories, lane exits and lane splits, is the concept of driver decision. The driver who is confident of his destination and the proper path thereto generally presents no conflict with the flow of traffic. The problem arises largely from those drivers who are inattentive, intoxicated, uncertain of how to reach their destination, and(or) have improper driving habits. It is these individuals, as shown in Figure 2, who conflict with the traffic stream. Therefore, it is imperative that the driver be made aware of the necessity for an early decision regarding his course of travel. The driver who makes an errant decision and abides by it is not as dangerous as the one who makes a delayed decision and attempts, often too late, to correct it. Thus, the driver who perchance takes the wrong branch is likely to resort to desperation tactics and back up or undertake some other maneuver that is illegal or contrary to safety.

The purpose of the study reported herein was to evaluate the operational characteristics of lane-drop situations as they are influenced by various fore-warning, decision-demanding messages. More specifically, the immediate purpose was to discover types of signs, pavement markings, and lane delineations which minimize or reduce erratic movements at existing lane drops. It was also hoped that an optimum design criteria for lane-drop situations might be determined.

Several standard and untried traffic control devices were selected for experimentation. A pilot study at a geographically advantageous location containing three lane splits was conducted. The results of this pilot study are the subject of this report.

Report Date

10-1-1971

Report Number

No. 313

Digital Object Identifier

http://dx.doi.org/10.13023/KTC.RR.1971.313

Notes

The opinions, findings, and conclusions In this report are not necessarily those of the Department of Highways or the Federal Highway Administration.

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