The National Academies Press

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Pages 36-53

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From page 36... ... • Downstream ATL length . Downstream lanes that are too short tend to discourage drivers who do not feel there is sufficient distance to comfortably merge into the CTL downstream . Read the entire page →
From page 37... ... In these situations, the practitioner must apply judgment in assess ing the anticipated safety and operational effects of the constrained ATL in order to determine the net benefit gained by the ATL. In some cases , the practitioner may find that a constrained ATL does not provide sufficient distance downstream of the intersection t o accommodate merge Exhibit 5-1 Unconstrained Site Exhibit 5-2 Direction of Flow Constrained Upstream ATL Direction of FLow Unconstrained Upstream ATL Constrained Site Read the entire page →
From page 38... ... These guidelines focus on an intersection confi guration that includes an upstream lane add and a downstream right - hand merge as illustrated in Exhibit 5 - 3 . Exhibit 5-3 Downstream ATL Length Upstream ATL Length (passive taper) Read the entire page →
From page 39... ... These guidelines focus on one - CTL and two - CTL facilities with intersections that have either a shared through/right outside lane or an exclusive right - turn lane. Exhibit 5 - 5 show s t he following range of options that can be considered for improving a one - CTL facility with out an exclusive right - turn lane : • Add a right - turn lan e • Add an ATL with a shared through/right lane • Add an ATL with an exclusive right - turn lane One-CTL Shared Through/Right Add Exclusive Right Add ATL with Shared Through/Right Convert Right to ATL with Shared Through/Right Add ATL with Exclusive Right Add ATL with Exclusive Right ExclusiveRight Two-CTL Existing Intersection Configuration Potential Improvements Exhibit 5-4 Design Approach Flowchart Read the entire page →
From page 40... ... Applying Existing Guidance The AASHTO Green Book does not provide guidance for ATLs at signalized intersections but includes information about auxiliary lane applications. However, the auxiliary lane discussions within the Green Book refer to highspeed facilities and free-flow conditions. Read the entire page →
From page 41... ... • Prior to the required signage, the "Right Lane Ends" W9 - 1 sign may be considered to emphasize that the trav el lane is ending. Exhibit 5 - 6 also illustrates the pavement markings (MUTCD Figure 3B - 14) Read the entire page →
From page 42... ... As illustrated in Exhibit 5 - 7 , there are four unique segments of the ATL that require driver action s that differ from those req uired by the geometric ATL design sections . These driver interpretation segments consist of Approaching ATL, Approaching Signal, Departing Intersection, and Merge at End of ATL. Read the entire page →
From page 43... ... Exhibit 5-8 Signing and Pavement Markings for Approaching ATL Segment Upstream ATL Length Read the entire page →
From page 44... ... A higher taper rate is appropriate for higher - speed locations. Local agencies typical ly have design guidelines for the introduction of an additional Exhibit 5-9 Analysis Steps for Determining Upstream ATL Length Passive Taper Step 1 Step 2 Step 3 Step 4 Step 5 Step 6 Step 7 Gather Input Data Select the ATL volume as the lower ATL flow rate from steps 2 and 3 Calculate performance measures for ATL and CTL Estimate the 95th percentile queues Determine minimum upstream ATL length • • • Total approach through and right-turn flow rates. Read the entire page →
From page 45... ... In addition, a s upplemental "Standard Through - Lane Arrow" should be considered at the start of the ATL to communicate the purpose of the added lane. Approaching Signal Segment When approaching the intersection, drivers should be reminded that the lane configuration on the approach to the intersection continues beyond the intersection. Read the entire page →
From page 46... ... P ractitioners should consider the appropriate design vehicle and potential impact to other users when selecting a curb - return radius . L arger curb - return radii or three - centered curves for right - turns result in less deceleration in the Exhibit 5-10 Signing and Pavement Markings for Approaching Signal Segment Exhibit 5-11 Appropriate Spacing between ATL Start and Right-Turn Lane Right-Turn Lane Curb Radii Read the entire page →
From page 47... ... Either the Mandatory Movement Lane Control signs (R3 - 5 or R3 - 5a) or the Optional Movement Lane C ontrol sign (R3 - 6) Read the entire page →
From page 48... ... ATLs with long downstream lengths may be perceived as a CTL and drivers may reach the end of the segment and realize unexpectedly that they are required to merge. From a review of the ATL study sites and other literature, it appears that a range of ¼ to ½ mile is an appropriate maximum value for downstream ATL length depending on prevailing speed, sight lines, and driveway/side-street activity. Read the entire page →
From page 49... ... The greater of the two distances should be used to determine the minimum downstream ATL length. Additional distance may be appropriate based on the prevailing traffic and geometric conditions of the ATL approach. Read the entire page →
From page 50... ... Page 51 Exhibit 5-13 Illustration of ATL Downstream Length (DSL1) Calculation Read the entire page →
From page 51... ... F or two - CTL sites, DSL 1 will most always govern the minimum downstream ATL length because of the higher volume of traffic and queue in the ATL. Exhibit 5 - 14 shows potential ATL downstream lengths based on a set of operational parameters for an anticipated congested level at one - CTL facilities, while Exhibit 5 - 15 illustrates potentia l ATL downstream lengths at two - CTL facilities. Read the entire page →
From page 52... ... Signing in this segment is needed to effectively communicate to drivers that the ATL is ending a specific distance beyond the intersection. To accomplish this, c onsider ation shoul d be given to providing a side - mounted "Right Lane Ends" W9 - 1 sign approximately 50 to 100 feet minimum from the crosswalk (extension of opposite stop bar) Read the entire page →
From page 53... ... In addition, supplemental "Lane Reduction Arrows" should be considered for speeds of 45 mph and higher. Exhibit 5-16 Signing and Pavement Markings for Merge at End of ATL Segment Geometric Design Guidelines Signing Guidelines Pavement Markings Guidelines Read the entire page →

From page 36...

... • Downstream ATL length . Downstream lanes that are too short tend to discourage drivers who do not feel there is sufficient distance to comfortably merge into the CTL downstream .