Guidelines on the Use of Auxiliary Through Lanes at Signalized Intersections (2011) / Chapter Skim
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Appendix A - A Simulation-Based Approach to ATL Evaluation
Appendix A - A Simulation-Based Approach to ATL Evaluation
Pages 66-74
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From page 66... ...
Principles of Lane Change Algorithms Microsimulation tools explicitly model the movement of individual vehicles using a series of behavioral rules known as algorithms. Among these, lane changing algorithms are most critical for accurately describing ATL behavior.
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From page 67... ...
As a result, no voluntary lane changes will take place past the upstrea m ATL decision point, and consequently no CTL - to - ATL maneuvers will take place past that point. In this context , it is important to emphasize that a coded upstream decision distance that is greater than the total ATL length will prevent any voluntary lane changes into the ATL and will therefore result in zero through flow on the ATL.
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From page 68... ...
The simulated ATL utilization percentages shown in Exhibit A-2 were the result of free lane selection by drivers on the intersection approach, subject to the algorithms of car-following, lane changing, etc. The ATL utilizations were not "forced" in the sense that a fixed percentage of through traffic was routed through the ATL.
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From page 69... ...
Ultimately, the following two explanatory variables were used in the LCD prediction model: Volume: through traffic flow rate expressed in vehicles per hour (vph) Upstream: the length of the ATL segment upstream of the stop bar, in feet The resulting model predicting LCD%TOTAL as a function of these two variables is given below: R 2 = 0.622 The R 2 value suggests that 62.2 percent of the variability in the LCD variable that provided the best match to the field data is explained by the variables in the model for the regression data set.
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From page 70... ...
No netheless, the SSAM output can still be used to examine relationships between conflict frequency and key ATL design elements such as downstream length. From the calibrated simulation models, SSAM uses the trajectory (*
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From page 71... ...
Rear - end conflicts remained relatively consistent as downstream length increased, but the numbe r of sideswipe conflicts spiked at a downstream length of 800 feet. This may be due to some quirk in the simulation or SSAM logic and the low sample size of sideswipe conflicts.
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From page 72... ...
While rear - end conflicts remained relatively unaffected by changes in downstream length, the number of sideswipe conflicts tended to increase as downstream length increased. This could be explained by the exposure, as a g reater downstream length tended to generate more conflicts in SSAM simply because the conflict area was lengthened .
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From page 73... ...
Proposed Work Flow of ATL Simulation Study If an analyst is studying the feasibility of an ATL intersection improvement, the following list of steps represent a proposed analysis work flow. Please note that additional steps may be necessary, depending on the specific location, and the practitioner should exercise sound judgment in any simulation analysis.
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From page 74... ...
To estimate ATL safety performance, the SSAM evaluation should be limited to the specific ATL link in question and should distinguish between rear - end and lane - changing conflicts, as well as conflicts in the upstream and downstream portions of the ATL. Depending on the objective of the analysis, it may be usef ul to obtain performance measures on a per - lane basis, to be able to isolate the performance of the ATL.
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