Edition foreslopes backslopes design speed design adt 6. The desired width is dependent upon the traffic volumes and speeds and. Aashto green book where establishing a fullwidth clear zone in an urban area is not practical due to rightofway constraints, consideration should be given to establishing a reduced clear zone, or incorporating as many clear zone concepts as practical such as removing roadside objects or making them crashworthy. Exceptions such as utility poles may only be approved by the county engineer. The weaving lengths presented in figure 1068 of the aashto green book are to be provided on lowvolume cloverleaf interchanges. For projects where the clear zone widths from the aashto are. Sight distance studies national association of city. Additional information is available in aashto s roadside design guide. Guidance included in the green book is based on established practices and is supplemented by recent research. When a site specific investigation indicates a high probability of continuing crashes, or when such occurrences are indicated by crash history, the designer may provide clear zone distances greater than the clear zone shown in table a21. The new aashto green book american public works association. This clear zone area is defined as anything between the heights of 3 ft and 10 ft, which often include buildings, signs, mailboxes, parked vehicles, wallsfences, vegetation etc. When aashto published a policv 011 geometric design of. A policy on geometric design of highways and streets also known as the green book, this guide was developed by the aashto standing committee on highways.
The difference between a clear zone and horizontal clearance or operational offset has been a topic of much confusion. Conversely, on most lowvolume, urban, or lowspeed facilities, a 30foot clear zone distance was considered excessive and seldom could be justified for engineering, environmental or economic reasons. Aashto s a policy on geometric design of highways and streets green book is currently used by most state departments of transportation in the united states in determining the design length of. The minimum horizontal clear zone width ft for a rural local road is most nearly. When designing urban roadway 29 reconstruction or improvement projects, the engineer should weigh the costs of clearing aboveground. Typical or expected road user types motor vehicles, trucks, transit buses, special vehicle types, pedestrians, bicyclists, disabled a p p e n d i x e the future aashto green book. Table 1 below contains some of the key points from the 2011 aashto green book to assist the designer in the evaluation. However, if this is an isolated obstacle and the roadway has no significant crash history, it may be appropriate to do little more than delineate the dropoff in lieu of foreslope flattening or shielding. Added language from the roadside safety hardware announcement made on january 1, 2016. Horizontal clearance must not be confused with clear zone. Until 23 cfr pai1 625 is updated through rulemaking procedure, the 2018 green book should be considered guidance only and the 2011 green book is still the adopted standard. Aashto green book, highway and street design best materials. The width of the clear zone will be as last documented in the design approval document, the project files, or in the contract. The minimum 18 inch horizontal clearance to objects behind curbs as specified in the aashto green book is a minimum standard offset allowing for normal traffic operations.
Key elements of the aashto green book model are described below. The unobstructed, traversable area provided beyond the edge of the through traveled way for the recovery of errant vehicles. A policy on geometric design of highways and streets pgdhs or green book. Its official title is a policy on the geometric design of highways and streets. Determining a practical clear zone often involves a series of compromises between absolute safety, engineering judgment, environmental and economic constraints. The aashto standard values for the items requiring a design exception will be based on higher of either the posted speed or the minimum green book value for design speeds of that particular type facility collector, arterial, etc. State of alaska department of transportation and public facilities. Definitions, terminology, policy horizontal clearance to ob struction renamed to lateral offset to obstruction recovery area replaced by clear zone. It provides guidance to engineers and designers who strive to make unique design solutions that meet the needs of highway and street users on a projectbyproject basis. May 01, 2020 nysdot defines the clear zone as that portion of the roadside border width, starting at the edge of the through traveled way, that the department commits to maintaining in a cleared condition for safe use by errant vehicles. This book, or parts thereof, may not be reproduced in any form without.
Pdf recommendations for acceleration lane length for. Design criteria the current design criteria for passing sight distance on two lane highways in the aashto green book 1 are based on the results of field studies 2, 3 conducted between 1938 and. Aashto policy on geometric design of highways and streets green book ansiiesna rp8 wisdot fdm 4115 fhwa highway functional classifications policy specifies using the aashto roadway lighting design guide october 2018, table 35a, which references the green book classifications. Sep 28, 2018 aashto said the latest edition of the green book presents an updated framework for geometric design that is more flexible, multimodal, and performancebased than in the past providing guidance to engineers and designers who strive to make unique design solutions that meet the needs of all highway and street users on a projectbyproject basis. Effectiveness of clear recovery zones, nchrp report. The aashto a policy on geometric design of highways and streets green book enumerates a clear zone value for two functional classes of. The manual of uniform minimum standards for design, construction and maintenance florida greenbook provides criteria for public streets, roads, highways, bridges, sidewalks, curbs and curb ramps, crosswalks, bicycle facilities, underpasses, and overpasses used by the public for vehicular and pedestrian travel.
For additional clear zone information refer to the 2004 aashto green book and the aashto roadside design guide. Clear zone and horizontal clearance geometric design design. Oct 30, 2009 27 the aashto green book, 1 recommends a minimum 18 inch urban fixed object setback, although 28 many agencies provide design guidance that specifies greater distances. Zone 2 feet minimum paved or planted aashto green book 6 feet desirable 2 to 4 feet for localcollector streets 5 to 6 feet for arterialmajor streets aashto peds 5 to 8 feet depending on context ite pedestrian through zone or clear width for unobstructed travel 4 feet minimum with passing spaces or 2foot paved buffer. Passing sight distance design for passenger cars and trucks. The additional clear zone space that is needed because a portion of the suggested clear zone falls on a nonrecoverable. Chapter 4 sign, signal, and luminaire supports, utility poles, trees, and similar roadside features. The aashto a policy on geometric design of highways and streets green book enumerates a clear zone value for two functional classes of highway. Aashto s geometric design guidelines for very lowvolume roads adt.
When the weaving volume in a particular weaving section exceeds 1,000 vph, the quality of service on the main facility deteriorates rapidly, thus generating a need to transfer the weaving section from the through. The clear zone includes shoulders, bike lanes, and. The minimum 18 inch horizontal clearance to objects behind curbs that is specified in the aashto green book is. Aashto subcommittee on design annual meeting portland, maine. These areas should be clear of obstructions that might block a drivers view of conflicting vehicles or pedestrians. A free powerpoint ppt presentation displayed as a flash slide show on id. Resolved, the subcommittee on design scod is tasked with developing this guidance, both in the short term next green book. Chapter 8safety design section 8a2 clear zones revision date. More information can be found in aashto s roadside design guide. Best practice lower cost safety strategies should be considered first. Clear zone is addressed in several different aashto publications roadside design guide green book guidelines for geometric design of very lowvolume local roads a guide to achieving flexibility in highway design. Foreslopes parallel to the flow of traffic may be identified as recoverable, nonrecoverable, or critical. Nysdot defines the clear zone as that portion of the roadside border width, starting at.
A clear zone, or clear recovery area, as defined in the aashto roadside design guide and the aashto green book is that portion of the roadside, within the highway rightofway as established by the highway. The majority of the time, the posted speed will be the control. The aashto green book contains the current design research and practices for highway and street geometric design. Resolved, the subcommittee on design scod is tasked with developing this. Sidewalks national association of city transportation. This area may consist of a shoulder, a recoverable slope, a nonrecoverable slope, andor a clear. Surface course will be extended to the outside edge of armor stone to maximize the clear zone. Work the problems below on e2 paper, or on the computer, scan and submit as a. The new aashto green book whats new in geometric design. Section 1 clear zonelateral offset guidelines introduction the term clear zone is used to describe the unobstructed, traversable area provided beyond the edge of the through traveled way for the recovery of an errant vehicle. American association of state highway and transportation officials. As per the 2011 aashto roadside design guide aashto rdg, the clear zone. The figure also may serve as a general guide in other than flat terrain and adjustments can be made in the length of the terminal vertical curves. The group noted that not only are traditional functional classifications for roadways such as local roads and streets, collectors.
When the green book and the roadside design guide were last updated, the aashto committees coordinated to dispel the misunderstanding that 2 feet actually, 18 inches behind a curb constituted a clear zone. Optimum urban clear zone distance national association of. Clear zone terminology coordinated with aashto green book. Aashto a policy on geometric design of highways and streets. Aashto publications related to clear zone inconsistencies between green book and the roadside design guide, etc. Table 31 suggested clear zone distances in feet from edge of through traveled lane. The clear zone includes shoulders, bike lanes, parking lanes and auxiliary lanes except those auxiliary lanes.
The two types of sight triangles are approach sight triangles and departure sight triangles aashto, green book, 2001. The total roadside border area, starting at the edge of the traveled way, available for safe use by errant vehicles. Cra urban design overlay district city staff and community. Appendix e the future aashto green book a performance. Clear zone is addressed in several different aashto. Aashto subcommittee on design annual meeting portland. Resolved, aashto should provide guidance to state dots and other users of the green book regarding flexibility in design. If such slopes are relatively smooth and traversable, the. Aashto roadside design guide, 4th edition july, 2015 errata.
For local roads and streets, a minimum clear zone of 7 to 10 feet is considered desirable on sections without curb. Highway design manual chapter 10 roadside design, guide rail. This area may consist of a shoulder, a recoverable slope, a nonrecoverable slope, andor a clear runout area. The width of the clear runout area is equal to portion of the clear zone distance that is located on the nonrecoverable slope. Green book table 105, minimum deceleration lengths for exit terminals green book figure 1073, typical twolane entrance ramps. Definitions, terminology, policy horizontal clearance to obstruction renamed to lateral offset to obstruction recovery area replaced by clear zone. The 2018 green book was developed through the typical aashto consensus process and is an incremental evolution of the 20 i green book. The american association of state highway and transportation officials recently released the 7th edition of its policy on geometric design of highways and streets manual commonly referred to as the green book which is considered by many to be the preeminent industry guide to current highway and street design research and practices. Conflicts with aashto publications related to clear zone ch2m hill, timothy r. Roadways with shoulders in rural environments, where speeds are higher and constraints are fewer, a clear zone. Delaware department of transportat ion clear zone, lateral. When defined as a lowvolume roadway, this design guideline may be used in place of guidelines defined in the reen g book, a policy on geometric design of highways and streets pgdhs 2.
Two types of clear sight triangles are considered in intersection design. Clear zone the clear zone is defined as the unobstructed, traversable i. Aashto issues second edition of lowvolume roads guidelines. Also refer to the aashto roadside design guide for additional source references. This book, or parts thereof, may not be reproduced in any. This study identified conflicts and inconsistencies on clear zone guidance contained in aashto publications and present the findings to the relevant aashto committees so they can revise the publications. Chapter 10 roadside design, guide rail, and appurtenances. Aashto tcgd meeting notes salt lake city, ut july 22. For 3r or reconstruction, existing curvature equal to or flatter than absolute minimum values may be retained unless crash history indicates flattening curvature. It has been published by the aashto, in one form or another, since the late 1930s. The clear zone includes shoulders, bike lanes, and auxiliary lanes, except those auxiliary lanes that function like through lanes. May 31, 2019 aashto added that its lowvolume roads geometric design guidelines can be used in lieu of applicable policies presented in its broader a policy on geometric design of highways and streets handbook, commonly known as the green book.
Clear zones are not affected by curbs being present. In 1977, aashto published the guide for selecting, locating, and designing traffic barriers which. Clear zone is addressed in several different aashto publications roadside design guide green book guidelines for geometric design of very. The values indicated in the table are based upon the current policy related to objects in clear zones as specified in.
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