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6.0 Summary of Recommendations

6.4.1 Approach Zone

Guideline Approach Zones Design Guideline 1
Title Queue Zone Lengths
Text The length of queuing zone should be based on estimated or actual peak hour queue lengths, determined by an analysis, plus an added safety factor, with a minimum of 200 feet. Design year traffic volumes should be used.
Commentary For plaza reconstruction and expansion, design should make use of a simulation model to calibrate existing plaza operations and to estimate plaza queuing and toll lane usage, or use professionally acceptable manual calculation methods (note: vehicle mix, daily/weekend/holiday profiles, and unusual demand generators). The analysis must account for increased usage of express lanes and ETC dedicated lanes, which is expected to reduce conventional plaza queuing in the future.


Guideline Approach Zones Design Guideline 2
Title Transition Zone Tapers
Text Transition zone tapers approaching the conventional plaza should use the minimum taper rates presented in the McDonald 19991 and McDonald and Stammer 20012 reports. The diverge tapers from the latter publication for speeds of 40 mph or less is specified as L=WS/105 and for speeds 45 mph or more and L=3/8 WS for speeds 45 mph or more, where L= minimum length (ft.), S= posted approach speed in mph, and W= offset distance in feet. Use of a smaller taper for wide plazas and a minimum taper of 10:1 for speeds less than 30 mph was recommended.
Commentary Reference the ITE Freeway and Interchange Geometric Design Handbook – Chapter 13 for further design information on taper rates.


Guideline Approach Zones Design Guideline 3
Title Proximity to On-ramp
Text If the distance to safely change lanes to access the express lanes after entering the mainline from an upstream interchange on-ramp is not sufficient, this movement should be physically prevented through the use of barrier or delineator separated auxiliary lane extensions.
Commentary Existence of an ETC dedicated lane or provisions to add one within the conventional plaza should minimize any inconvenience to the ETC customer.


Guideline Approach Zones Design Guideline 4
Title Express Lanes
Text The approach transition zone begins at the start of the gore where the conventional plaza and express lanes split.
Commentary For tunnel and bridge plaza approach zones, sensors and physical constraints should be deployed to prevent oversized trucks from entering a toll lane. Provisions for safely maneuvering the vehicle out of the plaza area are required.


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