MUTCD lane shifting transition vs. lane taper width requirements 2

[smp123069]

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

 

[TerryScan]

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."

 

[TrafficDesigner]

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.

 

[smp123069]

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

 

[ACtrafficengr]

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

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