Guidelines on the Use of Auxiliary Through Lanes at Signalized Intersections (2011) / Chapter Skim
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Pages 28-35
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From page 28... ...
In particular, the following ATL elements are critical to its safe operation: • Downstream length . A sufficient downstream ATL length and taper is needed to allow for safe merging operation into the adjacent CTL traffic stream by providing drivers with enough distance to accelerate and find acceptable gap s in the CTL traffic .
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From page 29... ...
Sites with an adequate view of the downstream ATL from the stop bar experienced more ATL use, presumably because drivers feel more comfortable using an ATL when they can see the entire downstream merge area . In addition, with a n adequate view of the end of the ATL , drivers in the ATL can plan for their merge back into the CTL more carefully .
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From page 30... ...
Page 31 Proportion of ATL Crashes Although a crash reconstruction analysis was not within the scope of this research, it is generally true that the rear - end and sideswipe crashes that are the types most likely to be related to ATLs are not typically as severe as other crash types such as angle, hea d - on, and run - off - road crashes. Exhibit 4 - 1 displays a breakdown of the field crash d ata obtained for all 16 sites by crash type.
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From page 31... ...
Page 32 Approach Number of Years Analyzed Rear End Crashes Sideswipe Crashes Total Crashes SB MD-2 at Arnold Rd * 9 57 13 112 NB MD-2 at Arnold Rd *
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From page 32... ...
Relationship Between Crashes and Congestion Exhibit 4 - 5 plots the number of rear - end crashes from 2006 to 2008 against the maximum X T obtained from field data collected in 2009 and 2010 . X T indicat es the level of congestion in the through - movement lanes assuming no ATL is present .
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From page 33... ...
Exhibit 4 - 6 displays the trend between rear - end crashes and average ATL flow observed in the field for each of the 16 sites . This exhibit does not indicate that more crashes occur at ATLs with higher flow rates -- consequently, it does not provide evidence that a well - utilized AT L is less safe than a poorly utilized ATL .
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From page 34... ...
In summary, the analysis of the data from the 16 study sites showed some re lationship s between rear - end crashes and congestion , between rear - end crashes and flow rates in the ATLs, and between sideswipe cra shes and ATL length . However, t he relationships are weak and causation is unclear in all cases , so practitioners should not over - interpret the findings .
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From page 35... ...
threshold of 1.5 seconds is preferred to yield a larger sample size . The practitioner should then look for the relative change in conflict frequency when a design element (e.g., downstream length)
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