Skip navigation to main content
United States Department of Transportation - Federal Highway Administration FHWA Homefeedback

6.0 Summary of Recommendations

6.4.2 Departure Zone

Guideline Departure Zones Design Guideline 1
Title Recovery Zone Lengths
Text The departure recovery zone should be equal to at least 200 feet and preferably 300 feet, a length expected to allow sufficient driver re-orientation, acceleration, and initial merge distance after exiting the plaza.
Commentary For tunnel and bridge toll plazas, a longer recovery zone may be warranted for oversized vehicles to safely maneuver out of the plaza area if sensors and physical constraints are not available or deployed to detect an oversized vehicle prior to entering a toll lane, thereby precluding any maneuver to exit the plaza on or before the plaza approach.


Guideline Departure Zones Design Guideline 2
Title Transition Zone Tapers
Text Transition zone tapers departing the toll plaza should use the minimum taper rates presented in the McDonald 19991 and McDonald and Stammer 20012 reports. The departure tapers presented in the latter publication for speeds of 40 mph or less is specified as L= (1.5)WS2/105 + 5W where L= minimum length of taper in feet, S+ posted departure speed in mph and W= offset distance in feet. For non-stop dedicated lanes, equations from the MUTCD and AASHTO “Green Book” should continue to be used for lane additions and subtractions.
Commentary Reference the ITE Freeway and Interchange Geometric Design Handbook – Chapter 13 for further design information on taper rates.


Guideline Departure Zones Design Guideline 3
Title Transition Zone Tapers
Text If the distance to safely change lanes to reach the exit lane of a nearby downstream interchange from an express lane is not sufficient, this movement should be physically prevented by a downstream extension of the raised median or barrier separating express lanes and merging conventional plaza lanes.
Commentary New construction should avoid potential information overload related to informing ETC users to exit the facility through the conventional plaza lanes in lieu of the express lanes by locating the plaza a sufficient distance from entry and exit ramps. For existing facilities, advance signing should be used to direct traffic that will be exiting at an interchange ramp just downstream of the plaza to use the conventional toll plaza lanes in lieu of the express lanes. Existence of an ETC dedicated lane or provisions to add one within the conventional plaza should minimize any inconvenience to ETC customers. The number of ETC dedicated lanes required should be calculated by estimating the percentage of ETC users exiting at a nearby downstream interchange ramp after traveling through a conventional plaza and or the percentage of ETC users entering the conventional plaza from a nearby upstream interchange on ramp. These percentages are then converted to volumes of dedicated lane ETC traffic and combined with an estimated residual of ETC traffic that elects to use the dedicated lane in lieu of the express lanes or all ETC mainline traffic if there are no express lanes.


Guideline Departure Zones Design Guideline 4
Title Express Lane Departure
Text The departure recovery and transition zones should be fully completed prior to the merge with continuing express lanes. (i.e. merged lanes should equal the number of lanes on the typical roadway section downstream of the plaza area), subject to provisions for merging with any express lanes.
Commentary An auxiliary lane may be used to temporarily increase the number of lanes merging with the continuing roadway lanes after exiting the conventional plaza.


Guideline Departure Zones Design Guideline 5
Title Recovery Zone Dedicated Lane Design
Text Placement of physical separation devices for dedicated lane traffic should be extended beyond the toll islands until traffic in the adjacent lanes that had stopped to pay the toll has accelerated to 50% of the operating speed. As a minimum, solid white striping should continue until the accelerating traffic has reached a point of approximately two-thirds (66%) of the operating speed based on the average acceleration rate of a mid-size vehicle.
Commentary Although specific locations are provided, the intent is to minimize the potential hazards of differential speeds when exiting a toll plaza.


Table of Contents | List of Tables | List of Figures | Previous Section | Next Section | HOME

FHWA Home | U.S. DOT | Operations Home | Privacy Policy
Federal Highway Administration - United States Department of Transportation