Star Sign up now to gain access to all the features of this website. NEW — access is now open to ALL USERS! — Already registered? Please log in.

Staff Traffic Engineer

Brad Julian
Staff Traffic Engineer was posted on December 22nd, 2011 at 5:15 PM EST
regarding Chapter 14: Multilane Highways

I was wondering if anyone had any good information on two different topics related to arterials. The first involves calculating required weaving lengths between two intersections. Is the methodology from 1984 (Jack Leisch) still considered valid? The second involves merging lengths on arterials. I've used the formulas in the past that rely on speed to calculate a merging taper. This seems to only be for short term situations such as work zones though. Is there any guidance on providing appropriate merging lengths for permanent lane reductions that takes into account speed, volumes and gap acceptance?

Erik Ruehr
VRPA Technologies
RE: Staff Traffic Engineer was posted on January 3rd, 2012 at 6:19 PM EST

I am replying as a non-expert on both issues, but perhaps some information that I can share would be helpful. Neither the 2010 HCM nor any other document that I know about has an official procedure for arterial weaving. Methodologies that I have seen used for this issue include simulation and use of a freeway weaving procedure modified by engineering judgment to account for the different characteristics of an arterial street. I don't think anyone has officially declared the Leisch weaving procedures to be invalid, so I think it is up to the individual analyst to decide whether those procedures can provide useful information to deal with arterial weaving. On the issue of merging lanes, the formulas based on speed from AASHTO and some state highway agenices are what I use for both temporary and permanent situations. I don't remember ever seeing a study of gap acceptance related to this issue.

Sign in to add a reply. Don't have an account? No problem, sign up for free.