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MUTCD lane shifting transition vs. lane taper width requirements
2

MUTCD lane shifting transition vs. lane taper width requirements

MUTCD lane shifting transition vs. lane taper width requirements

(OP)
Does anyone have any experience with the requirements for a lane transition/offset taper?

I have located the formula in Chapter 6 of the MUTCD which notes that you can use the L/2 for a transition taper where L is the taper length for a merging taper.

I have been told that the L/2 is only applicable to temporary traffic control since this is found in Chapter 6 of the MUTCD for temporary traffic control.

Part 3 of the MUTCD gives the same formula for the taper requirements but does not allow the L/2 to be used for a transition/offset taper. Part 3 of the MUTCD does not make any mention of the difference between a mering taper and a transition/offset taper.

The only reference I have found to the transition/offset taper is that of a transition across an intersection but there is no formula for this transition or maximum allowable offset noted.

Where can I find the length requirements for a permanent lane shifting/offset taper?

SMP

RE: MUTCD lane shifting transition vs. lane taper width requirements

The state DOT here uses the formula in MUTCD found on page 3B-5 and 3B-19 (as well as other locations in chapter 3):

"For three-lane roadways having a posted or statutory speed limit of 70 km/h (45 mph) or greater, the lane
transition taper length should be computed by the formula L = 0.62 WS for speeds in km/h (L = WS for speeds
in mph). For roadways where the posted or statutory speed limit is less than 70 km/h (45 mph), the formula
L = WS^2/155 for speeds in km/h (L = WS^2/60 for speeds in mph) should be used to compute taper length. Under
both formulas, L equals the taper length in meters (feet), W equals the width of the center lane or offset distance
in meters (feet), and S equals the 85th-percentile speed or the posted or statutory speed limit,
whichever is higher."

RE: MUTCD lane shifting transition vs. lane taper width requirements

We do it the same way as TerryScan stated.  Our State DOT uses WS for what they consider highspeed roadways or over 50 MPH and higher for a shift taper.  They allow WS/2 for 45 MPH or lower for a shift taper.

For merge tapers it's just L=WS.

Our County DOT uses L=WS for all tapers.

RE: MUTCD lane shifting transition vs. lane taper width requirements

(OP)
Thank you both for your responses. I appreciate your input.

We have been using the formulas that TerryScan referred to.

Intuitively I was thinking that there should be two formulas (for a design speed). I thought that you would have one formula for a lane shift where all of the lanes are shifting together and another formula for a lane shifting/merging into a 2nd lane. Evidentally I was incorrect.
Thank you both again!

SMP

RE: MUTCD lane shifting transition vs. lane taper width requirements

Now that you mention it, Ch. 3 doesn't seem to mention shifting tapers at all - just lane drop tapers and lane narrowing tapers.

About 8 years ago, when I worked for NYSDOT, we were given guidance from Main Office to use L/2 for permanent shifts. I haven't worked there in 7 years, so they may have changed their guidance since.

Please ask your question on http://knowledge.fhwa.dot.gov/cops/opspublic.nsf/home?openform. I'd like to see the responses you get.

     "...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

"I'm searching for the questions, so my answers will make sense." - Stephen Brust

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