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Passive Taper: The ATL taper upstream of the intersection that allows
vehicles to enter the ATL.
Active Taper: The ATL taper downstream of the intersection that requires
vehicles to merge.
XT: The demand-to-capacity ratio for the through movement assuming the
ATL is not in place.
APPLICATION
Similar to CTLs, ATLs are implemented to increase the stop-bar capacity on
approaches at signalized intersections that represent a "choke point" along an
arterial street. They can be applied in urban, suburban, or rural environments on
either the major-street or minor-street approach.
ATLs are often applied in lieu of a CTL when:
· Construction of a CTL is not feasible;
· The capacity added by the ATL adequately accommodates current or
projected traffic demand through the intersection bottleneck; and
· Sufficient length is available to accommodate upstream storage and
downstream merge activity.
CONFIGURATION TYPES
These guidelines address four types of ATL configurations as shown in
Exhibit 2-1:
· One CTL with a shared ATL
· One CTL, one ATL, and an exclusive right-turn lane
· Two CTLs with a shared ATL
· Two CTLs, one ATL, and an exclusive right-turn lane
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Exhibit 2-1
ATL Configuration Types
One CTL with Shared ATL
One CTL, One ATL, and Exclusive Right-Turn Lane
Two CTLs with Shared ATL
Two CTLs, One ATL, and Exclusive Right-Turn Lane
Each of the configurations shown in Exhibit 2-1 consists of a right-hand lane
addition upstream of the intersection and a right-hand merge downstream of the
intersection. Results from a web survey conducted as part of this research effort
found that 85 percent of ATL applications had both a right-hand lane addition
upstream and right-hand merge downstream. The remaining sites included
right-turn drop lanes downstream that generally ended at a commercial
driveway entrance or left-hand merges. The guidelines presented in this
document do not address ATLs with right-turn drop lanes and left-hand merges
given the relatively few known applications of that configuration.
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