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.

Outside Lane

n. r. voigt
Outside Lane was posted on October 21st, 2012 at 1:42 PM EDT
regarding Chapter 15: Two-Lane Highways

I thought we had dismissed the confusing subject of outside vs. inside lanes in previous editions, but the terms have crept back into the 2010 version. Particularly confusing: look at page 15-11. Which lane is the outside lane of a two-lane highway? I hope the PE exam does not use these terms, as the usage is not consistant accross the US. For crash reporting, some police training procedures number the lanes with the right-most lane (in the US) as the number 1 lane, but that becomes confusing when looking at old crash data if another lane has recently been added to the right side of the roadway, making the former number 1 lane now to be the number two lane. Another confusing term is middle lane, which on a four-lane roadway with two in each direction, could mean the lane nearest the median. For a six-lane roadway with three in each direction, which lane is the middle lane? And, going back to the original comment, which lane is the outside lane on a six-lane roadway? When going around a curve, the inside lane is usually the lane closest to the center of the circle, which has the smallest radius, hence the shortest site distance. In this case it would appear by some definitions the outside lane for traffic becomes the insidelane for geometry. An explanatory diagram in the introduction would help.

Gustavo Riente de Andrade
TECTRAN - T├ęcnicos em Transportes ltda
RE: Outside Lane was posted on October 21st, 2012 at 8:30 PM EDT

Is the "outside lane" terminology you mention the one that appear at the Bicycle LOS method? In this case, I believe it refers to the lane next to the shoulders. For a two-lane highway, generally there are only "outside lanes" in the carriageway, unless the analysed sections has TWLT or climbing lanes/passing lanes. In the first case, the outside lanes would be the regular ones; in the second, they could refer to the passing/climbing lanes.

Peyton McLeod
Sprinkle Consulting
RE: Outside Lane was posted on October 29th, 2012 at 12:07 PM EDT

Yes, the reference on page 15-11 is specific to the bicycle mode analysis. The width of the outside lane is a component of the base bicycle level of service model that shows up in several different chapters; it refers to the outermost general purpose travel lane (regardless of the presence/absence of paved shoulders). Within the context of a two-lane highway the "outside lane" loses some meaning, but is intended to refer to the one and only travel lane in each direction.

n. r. voigt
RE: Outside Lane was posted on December 16th, 2012 at 4:18 PM EST

Okay, according to MacLeod the "outside lane" for HCM purposes is the general purpose lane furthest from the median or centerline of a multilane roadway. I would presume then that the "inside lane" is the general purpose lane closest to the median. I cannot find this definition in HCM2010. The reason for clarification is I recall fom my trafic engineering university classes, and previous terminology research, that found the definition varies throughout the US (and perhaps Europe as well as I found from googling the term), just as lane numbering is not constant. To test the point, I did an informal survey of fellow traffic engineers that I know and did not come up with a consistant definition. To extend the survey, I asked a group of professional over-the-road and transit bus drivers and did not get anything clear either. Sometimes it was the right-most lane, and sometimes the left-most lane was called the outside lane. Mostly (from the bus driver's responses) there was complete puzzlement, as the term is not used in CDL terminology, nor other driving programs either I or they have worked with. I feel as engineers we need to be a bit more precise than that. To write a question on an exam or to use the phrase in a report to a client that is nebulus without proper definition is not being a responsible engineer. The simple solution: If TRB insists on using the term "outside lane," which does not have a consistant meaning, then please provide a definition within your publication and a diagram to show where the "outside lane" is located. Thanks to MacLeod for the clarification.

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