Adjustment factor for right-turn vehicle

[Hsmith17]

Hi- equation 18-10 in HCM is frt=1/Er. This is for right-turning only. Can anyone confirm how to calculate frt for a right turn movement that is shared with a through movement? Is it frt=1-(1/Er)*(Vrt//V)? (This is for question 12 in Ch1 of 6 min solutions- HCM refers to Ch 31 and I can't find the equation there.)

Thanks!

 

[ptatohed]

Hi- equation 18-10 in HCM is frt=1/Er. This is for right-turning only. Can anyone confirm how to calculate frt for a right turn movement that is shared with a through movement? Is it frt=1-(1/Er)*(Vrt//V)? (This is for question 12 in Ch1 of 6 min solutions- HCM refers to Ch 31 and I can't find the equation there.)

Thanks!

Perhaps I am not understanding your question completely but my understanding is that if right turns are present in the lane group, then the adjustment factor, fRT, is used. fRT is simply 1 / ER, and ER = 1.18, so fRT = 0.85.

 

[Atharaenea]

Hi- equation 18-10 in HCM is frt=1/Er. This is for right-turning only. Can anyone confirm how to calculate frt for a right turn movement that is shared with a through movement? Is it frt=1-(1/Er)*(Vrt//V)? (This is for question 12 in Ch1 of 6 min solutions- HCM refers to Ch 31 and I can't find the equation there.)

Thanks!

I saw that too. I suspect the HCM is in error, and the actual equation is 1-(1/Er)(Vrt/Vtot). The equation doesn't work otherwise, because you'd get a very low number for an answer. I just wrote in what I think is the correct formula, and I think that you should be able to reason the correct way during the test.

 

[Atharaenea]

Sorry, I meant to write more... I think it's that way because of the second paragraph explaining that equation in the HCM, where the right turn movement shares a lane, which is the case in the 6 minute solution problem. It refers us to chapter 31, which apparently is in volume 4 (and we don't have). Therefore I just took the equation in the 6 minute solution book as what we do in that situation. There's no way they'd ask us that on the PE though, since we're not required to bring volume 4. On the PE it'll probably just be 1/Er, if it's needed at all.

 

[P-E]

How about left turning vehicles?

 

[JessieZ]

Thanks for bringing this up. I saw this equation too in the solution. My guess this for shared used right turn lane, it will be explained in detail in volume 4. equation 18-10 in HCM is frt=1/Er is for exclusive right turn only. I also found there are errors of calculating LOS in the 6 min solution. I wondering if you guys feel the same way. The book uses FFS as the S when calculating the density.

 

[ptatohed]

Thanks for bringing this up. I saw this equation too in the solution. My guess this for shared used right turn lane, it will be explained in detail in volume 4. equation 18-10 in HCM is frt=1/Er is for exclusive right turn only. I also found there are errors of calculating LOS in the 6 min solution. I wondering if you guys feel the same way. The book uses FFS as the S when calculating the density.

I think this is just a sloppy job from when they updated the 6MS book from 2000 HCM to 2010 HCM. I would disregard all HCM 2000 stuff and disregard any HCM 2010 Volume 4 stuff. Did you guys check the errata on PPI's site for this book? You should report any suspected errata too.

http://emars.ppi2pass.com/errata/

 

[John QPE]

For this exam, and for pretty much all traffic operations unless you start getting super duper high speed theoretical frt = (1/Er) which is (1/1.18) all the time every time ....

If you look on page 18-35, you will see that frt = adjustment factor for right turn "presence" in a lane group.

 

[Atharaenea]

For this exam, and for pretty much all traffic operations unless you start getting super duper high speed theoretical frt = (1/Er) which is (1/1.18) all the time every time ....

If you look on page 18-35, you will see that frt = adjustment factor for right turn "presence" in a lane group.

What do you mean by traffic operations? I know 6 minutes solutions is harder than the test, but I sort of figured that 6 minute solutions would still leave me well prepared. Is there something else I should be learning about that this book won't lead me to?

 

[John QPE]

For this exam, and for pretty much all traffic operations unless you start getting super duper high speed theoretical frt = (1/Er) which is (1/1.18) all the time every time ....

If you look on page 18-35, you will see that frt = adjustment factor for right turn "presence" in a lane group.

What do you mean by traffic operations? I know 6 minutes solutions is harder than the test, but I sort of figured that 6 minute solutions would still leave me well prepared. Is there something else I should be learning about that this book won't lead me to?

(1/1.18) is all you need dude.