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Fitzpatrick and Wolff 1
2nd Urban Street Symposium (Anaheim, California) — July 28-30, 2003
Left-Turn Lane Installation guidelines
By
Kay Fitzpatrick
Research Engineer
Texas Transportation Institute, 3135 TAMU
College Station, TX 77843-3135
phone: 979/845-7321, fax: 979/845-6481
email: K-Fitzpatrick@tamu.edu
Tim Wolff
Graduate Assistant Researcher
Texas Transportation Institute, 3135 TAMU
代写英国论文College Station, TX 77843-3135
phone: 979/845-9903, fax: 979/845-6481
email: T-Wolff@ttimail.tamu.edu
Submitted for 2nd Urban Street Symposium Sponsored by Transportation Research Board
July 2003
ABSTRACT
The addition of a left-turn lane can improve the operations and safety at an intersection.Guidelines as to when to include a left-turn lane in intersection design are plentiful. Because ofthe quantity of methods, questions are asked regarding which method to use. This paperreviewed eight selected techniques and a number of criteria present in state manuals. Methodsbased on delay typically do not recommend a left-turn lane at lower left or through volumeswhen compared to methods based on conflict avoidance or safety. Because of the high benefitsfor crash reductions provided by left-turn lanes, a method that results in a recommendation atlower volumes would be preferred. The Harmelink model is a widely accepted approach that isbased on conflict avoidance. The procedure was first proposed in 1967 and includesassumptions that may need to be revised. Findings from current research would suggest a criticalgap of 5.5 sec (rather than 5.0 sec), a time to make left turn of 4.3 sec (rather than 3.0 sec), and atime to clear the lane of 3.2 sec (rather than 1.9 sec). A table was developed that lists suggestedguidelines for installing left-turn lanes for operating speeds of 30, 50, and 70 mph (50, 80, and110 km/h).
Fitzpatrick and Wolff 22nd Urban Street Symposium (Anaheim, California) — July 28-30, 2003
BACKGROUND
The addition of a left-turn lane can improve the operations and safety at an intersection. A recentFHWA study found that the addition of a left-turn lane can result in reductions of crashes from 7to 48 percent.1 Other studies have demonstrated the benefits of delay reductions with theinstallation of a left-turn lane on two-lane highways.2 Guidelines as to when to include a leftturnlane in intersection design are plentiful. Some are based on minimizing conflicts in terms ofthe occurrence of a through vehicle arriving behind a turning vehicle; others are based ondecreasing the amount of delay to through vehicles, and some are based on consideration ofsafety. Because of the quantity of methods, questions are asked regarding which method to use.
For example, are certain techniques better for a rural versus an urban setting? Do the evaluationsdiffer for number of lanes and for type of intersection? This paper reviewed eight selectedtechniques and a number of criteria present in state manuals. Some of the assumptions used inthe techniques will be reviewed, and suggestions on changes to selected guidelines will be made.Common terms are used in several of the techniques. Figure 1 graphically shows the followingmovements that are used to determine the need for a left-turn lane in several of the guidelines:
• Advancing Volume (VA) – the total peak hourly volume of traffic on the major roadapproaching the intersection from the same direction as the left-turn movement underconsiderat本论文由英语论文网提供整理，提供论文代写，英语论文代写，代写论文，代写英语论文，代写留学生论文，代写英文论文，留学生论文代写相关核心关键词搜索。