Quiz #17

[ptatohed]

This is probably more AM level, but here goes:

A traffic stream has mean time headways of 2.4 seconds. If the jam density is 51.0 vehicles

per mile, the optimum speed is 60.0 miles per hour, and the flow is 1,500 vehicles per hour, the

capacity of the highway, in vehicles per hour, is most nearly:

A) 1500

B) 1530

C) 1575

D) 1675

 

[John QPE]

Definitely PM topic.

B - 1530 veh/hr

Work per request.

 

[ptatohed]

Definitely PM topic.

B - 1530 veh/hr

Work per request.

Thanks Johnny-Q.

I think this topic falls more into the AM's VI. C. Traffic volume (e.g., vehicle mix, flow, and speed) but there might be some overlap with some of the PM topics.

https://cdn.ncees.org/wp-content/uploads/2012/11/Civ-Tran-April-2015_Combined.pdf

Anyone else with an answer?

 

[nda]

I second John with B. Thanks for posting this though

 

[John QPE]

Do we have an answer?

 

[ptatohed]

You guys are correct, answer B. John, you want to show everyone how it's solved?

 

[John QPE]

Step 1 - Solve for Free Flow Speed Uf

Uf = (U0)(2)

= (60)(2) = 120 mph

Step 2 - Solve for qcap

qcap = (Uf * Kj) / (4)

= (120 * 51) / 4

= 1530 veh/hr

 

[ptatohed]

Step 1 - Solve for Free Flow Speed Uf

Uf = (U0)(2)

= (60)(2) = 120 mph

Step 2 - Solve for qcap

qcap = (Uf * Kj) / (4)

= (120 * 51) / 4

= 1530 veh/hr

:clap:

 

[baileyhewes]

Alternative to that equation which isn't very intuitive, you can just remember optimum density is half of jam density. And optimum speed*optimum density = capacity. So just divide your jam density by 2 and multiply by 60. Same answer, its just easy to remember something if it makes sense in my head.

 

[GoldfishJack]

Step 1 - Solve for Free Flow Speed Uf

Uf = (U0)(2)

= (60)(2) = 120 mph

Step 2 - Solve for qcap

qcap = (Uf * Kj) / (4)

= (120 * 51) / 4

= 1530 veh/hr

:clap:

Where can I find these equations?

 

[ptatohed]

Step 1 - Solve for Free Flow Speed Uf

Uf = (U0)(2)

= (60)(2) = 120 mph

Step 2 - Solve for qcap

qcap = (Uf * Kj) / (4)

= (120 * 51) / 4

= 1530 veh/hr

:clap:

Where can I find these equations?

This is the first time I have plugged my own study guide on this forum but I will because it answers your question. I spent a lot of time to ensure all of the formulas you will need for the PE Exam, Transportation AM topics, are clearly presented in this study guide (Circular Curves, Vertical Curves, Traffic Volume):

http://www.learncivilengineering.com/transportation-study-guide-am/

If you have any questions about it, just ask.

 

[John QPE]

I never knew you had that!

I would've used that had I known.

Jack, these are fundamental traffic flow concepts, IMO these are going to be on the very fringe of what you would see on the AM. These are definitely PM topics you need to know, understand, and be able to manipulate. You'll find these concepts in any traffic engineering text: flow rate, headway, density, free flow speed, optimum speed, jam density, etc.

They are all inter-related.

 

[GoldfishJack]

I never knew you had that!

I would've used that had I known.

Jack, these are fundamental traffic flow concepts, IMO these are going to be on the very fringe of what you would see on the AM. These are definitely PM topics you need to know, understand, and be able to manipulate. You'll find these concepts in any traffic engineering text: flow rate, headway, density, free flow speed, optimum speed, jam density, etc.

They are all inter-related.

Understood John. I'm a bit rusty on TE topics so bear with me. Working my way through HCM as we speak.

 

[John QPE]

I never knew you had that!

I would've used that had I known.

Jack, these are fundamental traffic flow concepts, IMO these are going to be on the very fringe of what you would see on the AM. These are definitely PM topics you need to know, understand, and be able to manipulate. You'll find these concepts in any traffic engineering text: flow rate, headway, density, free flow speed, optimum speed, jam density, etc.

They are all inter-related.

Understood John. I'm a bit rusty on TE topics so bear with me. Working my way through HCM as we speak.

Not the whole thing I hope???

 

[GoldfishJack]

I never knew you had that!

I would've used that had I known.

Jack, these are fundamental traffic flow concepts, IMO these are going to be on the very fringe of what you would see on the AM. These are definitely PM topics you need to know, understand, and be able to manipulate. You'll find these concepts in any traffic engineering text: flow rate, headway, density, free flow speed, optimum speed, jam density, etc.

They are all inter-related.

Understood John. I'm a bit rusty on TE topics so bear with me. Working my way through HCM as we speak.

Not the whole thing I hope???

I'm working through Vol. 2 and making sure I understand how to calculate capacity, LOS, and FFS for different facilities (tabbing along). I ordered Mansour's book last weekend and hope to see it by the end of the week.

 

[John QPE]

OK .... spend a lot of time on Chapters: 4, 11, 14, 18, 23

 

[GoldfishJack]

Sounds good. Thanks John.

 

[John QPE]

No problem ..... now get to it. You only have a month!!

 

[ASchmidt]

I understand the solution to the problem, but there is also an equation for capacity in Vol. 1: v = 3600 / headway, which gives you an answer of 1,500 vph which is incorrect. Can someone explain this (forgive me I'm just getting into the HCM).

 

[John QPE]

I understand the solution to the problem, but there is also an equation for capacity in Vol. 1: v = 3600 / headway, which gives you an answer of 1,500 vph which is incorrect. Can someone explain this (forgive me I'm just getting into the HCM).

That equation is for flow rate, not capacity. Don't get confused.

Flow rate is variable ..... it depends on headway. If no one is on the road in the middle of the night and headway is 10 sec what do you have? A much lower flow rate.

Capacity is a function of the characteristics of the roadway.