Guidelines on the Use of Auxiliary Through Lanes at Signalized Intersections (2011) / Chapter Skim
Currently Skimming:
Pages 14-27
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 14... ...
It is founded on a method to predict the volume of traffic that will use an ATL. In addition to evaluating ATL and intersection performance, t he results from the operational analysis are needed to determine the recommended minimum design length s for the upstream and downstream ATL described in Chapter 5.
|
From page 15... ...
The two exhibits display location information, ATL length components, whether the ATL is exclusive or shared, and the level of ATL utilization by through traffic. ATL utilization in this context is defined as the percentage of approach through traffic, calculated by divid ing ATL through volume by the total through volume on the approach.
|
From page 16... ...
ATL Utilization % Through NB MD 2 at Arnold Annapolis, MD Exclusive 800 300 15 19 22 SB MD 2 at Arnold Annapolis, MD Exclusive 1670 1060 13 20 31 EB MD 214 at Kettering Bowie, MD Exclusive 830 510 2 5 8 NB IL 171 at IL 64 Melrose Park, IL Shared 890 1000 13 18 24 SB IL 171 at IL 64 Melrose Park, IL Shared 1150 830 14 18 23 NB IL 171 at Roosevelt Melrose Park, IL Shared 290 230 4 6 9 SB IL 171 at Roosevelt Melrose Park, IL Exclusive 450 360 21 26 30 SB US 1 at New Falls of Neuse Wake Forest, NC Exclusive 470 1040 11 13 15 EB = Eastbound, WB = Westbound, NB = Northbound, SB = Southbound Effect of Traffic Congestion on ATL Utilization The primary motivation for a driver to use an ATL is to save travel time by either avoiding long queues by moving around slower vehicles or avoid ing waiting at the light for mo re than one signal cycle (cycle failure)
|
From page 17... ...
to yield the corresponding 15 - minute pe ak flow rate. The relationship shown in the exhibit between congestion and ATL use is relatively strong, and more evident than a relationship between through traffic and the percentage of ATL utilization, expressed as a fraction of all through traffic.
|
From page 18... ...
Page 19 EB = Eastbound, WB = Westbound, NB = Northbound, SB = Southbound E1 = Exclusive, one CTL; S1 = Shared, one CTL; E2 = Exclusive, two CTLs; S2 = Shared, two CTLs Many of the figures and tables in this report have been converted from color to grayscale for printing. The electronic version of the report (posted on the web at www.trb.org)
|
From page 19... ...
E quation 3 - 1 computes the v /c ratio for the CTL s only because that factor was found to be the primary motivator for using the ATL. Also, all calculations should be based on 15 - minute flow rates, including the average green and cycle time, in the event that the traffic signal is actuated.
|
From page 20... ...
Page 21 EB = Eastbound, WB = Westbound, NB = Northbound, SB = Southbound E1 = Exclusive, one CTL; S1 = Shared, one CTL; E2 = Exclusive, two CTLs; S2 = Shared, two CTLs Exhibit 3-6 ATL Flow vs. Level of ThroughMovement Congestion (XT)
|
From page 21... ...
Exhibit 3-7 Minimum, Average, and Maximum ATL Utilization vs. Downstream Length Downstream Length (ft)
|
From page 22... ...
From a design perspective, the downstream ATL length should be long enough to enable drivers starting from a stopped queue in the ATL to accelerate to a safe merging speed. It should also allow drivers traveling through the intersection during the green phase to find a suitable gap for merging into the adjacent CTL traffic stream.
|
From page 23... ...
The upper bound estimate also gu arantees consideration of right - turn traffic effects, even for those cases where field observations did not show an impact due to low right - turni ng movements. While the method predicts ATL volume, the utilization percent age can be calculated from the results if desired.
|
From page 24... ...
The remaining flow rate in the continuous lane, V CTL , is obtained by subtracting V ATL from VT. This method can be used to estimate ATL use on approaches with one CTL in situations when the ATL will be an exclusive lane and when it will be a shared lane with right turns.
|
From page 25... ...
Therefor e, if an exclusive ATL is contemplated, the upper bound for the ATL through flow rate for the single CTL case can be estimated using Equation 3 - 6: V ATL,MAX In the case of two CTLs, the upper bound is computed using Equation 3-7: V ATL,MAX = w here: V ATL,MAX = U pper bound for ATL through flow rate, in vehicles per hour; and f LU = HCM 2010 lane utilization factor (see HCM 2010; Exhibit 18 - 30 for default values)
|
From page 26... ...
Page 27 S R = T he right - turn saturation flow rate in vehicles per hour . NUMERICAL ILLUSTRATION OF ATL VOLUME PREDICTION A two - CTL approach carries a through traffic flow rate of 1 , 000 vehicles per hour along with 191 right turns per hour in an exclusive right - turn pocket during the peak 15 - minute period.
|
From page 27... ...
The estimated exclusive ATL flow rate is the lower of the two estimates at 202 vph, and the per - lane through f low rate in the CTLs is (1,000 – 202)
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.