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MUTCD lane shifting transition vs. lane taper width requirements
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Source：Internet Author：Unknow Pubdate：2008-05-09
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smp123069 (Civil/Environme)
11 Dec 07 12:28
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? 字串9
SMP
TerryScan (Civil/Environme)
12 Dec 07 9:39
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."
字串9
TrafficDesigner (Civil/Environme)
12 Dec 07 13:52
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 (Civil/Environme)
13 Dec 07 9:49
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! 字串4
SMP
ACtrafficengr (Civil/Environme)
17 Dec 07 15:39
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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