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4.0 Geometric and Safety Design

4.5.3 Recommended Guidelines

Island Design Issues and Guideline Development

Some of the significant issues to consider when designing a toll island and recommendations for resolving these issues include the following:

Island Design and Tollbooth Protection Guidelines

Guideline Island and Tollbooth Protection Design Guideline 1
Title Island Width
Text The island width should be a minimum of six (6) feet, subject to a minimum of one (1) foot of clearance on each side of the toll booth or combined booth and ACM/ATIM equipment. For standalone ACM/ATIM equipment lanes, the width should be based on safe clearance for servicing (e.g., changing coin vaults, stacking tickets, maintenance servicing) the equipment, subject to the recommended minimum.
Commentary Design must consider an acceptable clearance offsets for ACM/ATIM equipment from the curb face for customer convenience during transactions.


Guideline Island and Tollbooth Protection Design Guideline 2
Title Island Length
Text Although the length of a toll island can vary from longest for manual collection to shortest for ETC dedicated lanes based on the design of island access facilities (e.g., stairwell, stairway) toll collection and traffic control equipment, and tollbooth and equipment protection, toll island length in a conventional plaza should be uniform. Specifically, the length of a manual island depends on the design of the tollbooth; design of any stairway for an overhead walkway or stairwell for an access tunnel; provisions for violation enforcement and traffic control equipment; tollbooth protection; design of canopy supports; provisions for staff access across the islands; and aesthetic considerations.
Commentary A possible exception to the manual lane being the control island length is when ACM/ATIM equipped lanes (i.e., automatic lanes) permit truck use and thereby deploy a pre-classification subsystem that requires a minimum 5-axle truck length prior to the ACM/ATIM equipment so the correct toll or class can be displayed or printed to the ticket, respectively.


Guideline Island and Tollbooth Protection Design Guideline 3
Title Impact Attenuator/Crash Cushions
Text Impact Attenuator/Crash cushions for cash lanes should be designed for a selected percent above the posted approach zone speed limit, but not less than 5 mph. For existing plazas, this percentage should be determined from field studies. Each impact attenuator/crash cushion type has specific requirements relative to cross slopes, grades, curbs, etc. Consequently, profile grades and cross slopes for new construction should be designed per the specification of the impact attenuator/crash cushion.
Commentary Pavement markings offering warning to approaching motorists should be considered for placement immediately in front of the impact attenuator/crash cushions, in the form of a gore taper with diagonal striping or tapered chevrons.


Guideline Island and Tollbooth Protection Design Guideline 4
Title Rampart and Crash Blocks
Text Tollbooth protection provided by rampart and crash blocks should be designed to withstand anticipated loads of design vehicles. The rampart should be designed to redirect errant vehicles. Crash blocks are constructed of reinforced concrete and can incorporate aesthetic features such as planters.
Commentary Double blocks should be considered if large vehicles are permitted. Longer blocks may be considered in lieu of a rampart. Design should be performed by an experienced structural engineer. If planters are used, any planted vegetation should not block the collector’s vision of approaching vehicles.


Guideline Island and Tollbooth Protection Design Guideline 5
Title Staff Access
Text Grade separated access to toll islands should be considered so no more than a single lane must be crossed to gain access to the intended island. Design should include use of warning devices (pedestrian gates, moveable barrier, chains, signs etc.) at the edges of the toll island to raise awareness of passing vehicles to staff crossing lanes. Two alternatives for grade-separated access are an access tunnel immediately below the tollbooth and an overhead walkway. In addition to stairway access to these facilities, for new construction ADA regulations may require the inclusion of elevator access subject to official job descriptions and minimum requirements to perform the work.
Commentary If using a pedestrian gate or moveable barrier, when “open” it should not extend into the adjacent toll lane.

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