Lindberg Civil PE Sample Exam, 4th edition Problem 193

[Predgw]

4 leg Intersection in an urban area, speed is 45 MPH, width of each leg is 48'. Average length of vehicle is 20', deceleration is 11.2ft/sec. Piev is 2.0 seconds

clearance time is included in yellow interval.

What is most nealry the min yellow time

A.2.5 secs

B. 4.0

C. 5.5

D 6.0

I got the answer correct, however the solution uses an odd formula. I looked at the clearnce time, then calculated the time needed to stop from a speed of 45MPH using deceleration of 11.2. Lindberg adds the PIEV time to the clearance time then adds that to the deceleration time but doubles the deceleration rate. t= v/2a

I approached this as the min yellow time would be the longer of the times when comparing the time needed to slow down versus the time needed to clear the intersection.

Where is the t=v/2a coming from and is my approach valid?

Thanks

 

[ptatohed]

Can you tell us what your/the book's answer is please?

 

[Predgw]

I believe it was 5.98 seconds.

 

[ptatohed]

Oh, by the way, I recognize the v/2a formula you ask about from the NCEES FE Handbook (which likely comes from some other reputable source). Under the Civil Transpo section (pg 164 of Version 9), they have a formula for y = v / (2a +/- 64.4G) where y = length of yellow (s), v = vehicle speed (fps), a = decel rate (ft/s2), and G = street grade (decimal %).

This yields y = 66 / (2 x 11.2 + 0) = 4.95 s.

Since 5.0 s is not one of the answer choices, I think when the problem statement says "clearance time is included in yellow interval", I think they mean the yellow time includes the red time?

Per the Handbook, same page:

r = (W + l) / v where r = length of red clearance (s), W = width of intersection (ft), l = length of car (ft), and v = vehicle speed (fps).

This gives r = (48 + 20) / 66 = 1.03 s

4.95 s + 1.03 s = 6.0 s

Is the answer D?

 

[ptatohed]

I believe it was 5.98 seconds.

Sorry, I was typing while you were responding. So, if the answer is D, then note the formulas I mentioned above from the FE Handbook.

How did you do your math? Your method might be perfectly valid too.

 

[Predgw]

My logic was the min yellow time ( which includes clearnace ) would be the longer of time to either;

continue through the intersection and clear the intersection,

or the time needed to slow the vehicle from 45 MPH to 0 MPH at the stop bar.

In both cases, there is a point where the motorist makes a decision that they can either make it, or they need to stop. Using t= V-Vo/a yields 5.9 seconds. So it would take 5.9 seconds to slow the vehicle down. .

I do not have the Lindberg book in front of me right now to double check but I think they left a ^2 off one of their calculations.

The distance needed to slow from 45 to 0 is V^2-Vo^2/ 2A that equals 194.47'

The distance needed to clear the intersection is 68'

Add the 68' to the 194.7 yields 262.47'

262.47'/ 66ft/sec= 3.98 seconds

add the 2 seconds PIEV yields the 5.98 seconds. I originally just used V-V0/(a)

I think I just lucked into the correct answer. If they listed a PIEV of 3 seconds, I would have got the answer wrong.

The formulas you listed are from the FE book? Are they in the CERM as well?

Thanks

 

[ptatohed]

Ok, I looked into this. It appears that the NCEES FE Handbook got their formulas from the ITE Traffic Engineering Handbook.

[SIZE=medium]http://redlightrobber.com/red/links_pdf/Application-of-the-ITE-Change-and-Clearance-Interval-Formulas-in-North-Carolina.pdf[/SIZE]

[SIZE=medium]http://www.thenewspaper.com/rlc/docs/armey/94intervals.pdf[/SIZE]

However, the ITE TEH was recently removed from the list of PE Transpo depth references. So, in theory, you shouldn't be tested on formulas from the ITE handbook on the PE exam. But 'Traffic Analysis - Traffic Signals' is still on the exam outline. ?

No, I do not see these ITE formulas in the CERM.

The way I first wanted to solve this is by calculating, from a simple uniform acceleration formula, the time it would take to stop a vehicle traveling 45mph plus reaction time. As you said, the time to stop from 45mph is 5.9sec. But that does not include the 2 sec reaction time. So, if you did it that way, you'd be at 8 sec. Too high.

I like the way you solved the problem by first calculating the distances. It seems to me this is a valid approach (no pun intended).

 

[Predgw]

Ok

Thanks for looking at this.

 

[Predgw]

In my Goswami All and One Civil Breadth and Depth book, page 806 equation 410.7; yellow interval may be calculated as y= Tr+ (W+L)/1.47 V x 1.47V/(2a+64.4G)

This references the ITE book which is no longer listed as a reference ( as you mentioned Ptatohed). So, I'm wondering what this equation is replaced with? Or is it buried in the pages of one of the three binders of the HCM 2010.

Anybody know?

 

[ptatohed]

[SIZE=10.5pt]Unfortunately, I do not think you'll find a calculation for Y or Y + R in the MUTCD or HCM. [/SIZE]

[SIZE=10.5pt]The MUTCD says Y should equal 3 to 6 seconds (see page 489)[/SIZE]

[SIZE=8pt]A yellow change interval should have a minimum duration of 3 seconds and a maximum duration of 6 seconds. The longer intervals should be reserved for use on approaches with higher speeds.[/SIZE]

[SIZE=10.5pt]The HCM basically says the same thing (see page 18-19) (see also pages 18-39/40 and 18-76)[/SIZE]

[SIZE=8pt]Yellow Change and Red Clearance[/SIZE]

[SIZE=8pt]The yellow change and the red clearance settings are input for each signal phase. The yellow change interval is intended to alert a driver to the impending presentation of a red indication. It ranges from 3 to 6 s, with longer values in this range used with phases serving high-speed movements. The red clearance interval can be used to allow a brief time to elapse after the yellow indication, during which the signal heads associated with the ending phase and all conflicting phases display a red indication. If used, the red clearance interval is typically 1 or 2 s.[/SIZE]

[SIZE=10.5pt]HCM Exh 18-28, 'Default Values', says to use Y + R = 4.0 seconds (but the footnote says “Specific values of yellow change and red clearance should be determined by local guidelines or practice.”)[/SIZE]

[SIZE=10.5pt]Lastly, the MUTCD says to refer to ITE!!!! (see page 485)[/SIZE]

[SIZE=8pt]Engineering practices for determining the duration of yellow change and red clearance intervals can be found in ITE’s “Traffic Control Devices Handbook” and in ITE’s “Manual of Traffic Signal Design”[/SIZE]

[SIZE=10.5pt]Also, check this out. [/SIZE]

[SIZE=10.5pt]Not sure if I helped (or made it more confusing!), sorry. [/SIZE]

P.S. Also, remember the quick rule of thumb: The vehicle speed (in MPH) divided by 10 = the Y + R (in sec). Ex. 55MPH = 5.5 sec yellow change + red clear. I'm not sure if that includes reaction time or not though. ?

 

[Predgw]

This reminds me of some contracts I have worked with... a garden path to the starting point. LOL Thanks for the info. I wonder why the ITE was pulled as a reference? I believe this is the first exam with that reference pulled, is that true? I guess if there is a problem of this nature my method for solving could work. I just like to be prepared and would rather be able to tab and refer to the proper formula. Thanks for the rule of thumb. I appreciate the response and the time to reference the page numbers.

I would say this board in general has helped me alot. The advice and information has been very very helpful. I plan to only take the exam only once and things are looking very good for that.

Thanks

 

[ptatohed]

This reminds me of some contracts I have worked with... a garden path to the starting point. LOL Thanks for the info. I wonder why the ITE was pulled as a reference? I believe this is the first exam with that reference pulled, is that true? I guess if there is a problem of this nature my method for solving could work. I just like to be prepared and would rather be able to tab and refer to the proper formula. Thanks for the rule of thumb. I appreciate the response and the time to reference the page numbers.

I would say this board in general has helped me alot. The advice and information has been very very helpful. I plan to only take the exam only once and things are looking very good for that.

Thanks

lol, good analogy. I heard (probably just a rumor?) that the ITE was pulled because they wanted to gear the exam more toward transportation and less toward traffic. But Traffic Analysis and Traffic Safety make up more than 1/3 of the PM exam, so go figure. No, I think the ITE TEH has been removed from the NCEES list of references for 1-2 years now. When I took the exam (April 2011), I think it was still on the list (but I never did obtain it). Glad I could help.

 

[Predgw]

Interesting, you took the exam without the ITE? Did you have the TRDM from Voight, or something similar? I have the TRDM as well as the Goswami PE Breadth and Depth which is a pretty good book. There is alot of useful information in there. For example, the Green book, table 3-2 gives SSD for 3%,6%,9% grades. Goswami has a table for SSD with 2%, and 4%. Not a huge deal as they are easy to caluclate, but if needed you could just look this up. I also like the index as the book is smaller. For a Pitot tube, I quickly found the equation which was laid out very clear.

Thanks

 

[ptatohed]

Interesting, you took the exam without the ITE? Did you have the TRDM from Voight, or something similar? I have the TRDM as well as the Goswami PE Breadth and Depth which is a pretty good book. There is alot of useful information in there. For example, the Green book, table 3-2 gives SSD for 3%,6%,9% grades. Goswami has a table for SSD with 2%, and 4%. Not a huge deal as they are easy to caluclate, but if needed you could just look this up. I also like the index as the book is smaller. For a Pitot tube, I quickly found the equation which was laid out very clear.

Thanks

Nope, I had the CERM, the All-In-One, and the main NCEES references (HCM, GDHS, RDG, and MUTCD) only.

 

[ptatohed]

Oh, and it is Lindeburg, by the way.

(and there is no such word as 'alot')

 

[Predgw]

Ohhh now this reminds me of my buddy that let me use his green book for the exam.

He lives to correct English. I write all my emails to him in fragmented sentences with poor spelling. Lol