Error or Engineering Judgement?

[Predgw]

Goswami All in One depth exam, problem 518. The question ask for the Minimum width measured from the edge of the 8' shoulder which should be free of obstructions.

This is a 2 lane rural freeway with 12' lanes. The ADT is 16,000 and the design speed is 65 MPH. The foreslope off the shoulder to the edge of a tree is shown as a 1V:4H.

Page 3-3, Table 3-1, of the 2004 RDG shows a range of 38'-46' for the speed and ADT given. Since the answer is asking for the distance from the shoulder, I picked 30' as an answer because it is asking for the min. distance. The answer in the book ( the units are incorrect) states the clear zone should be 46', so the answer is 38'

I tend to think this is an error, more so because the units are incorrect as well. The RDG states the clear zone distance is not a precise distance, but rather an approximate center range.

Any thoughts

 

[ptatohed]

Pred,

I have with me Goswami's PDF Transpo Depth practice exam from 06-15-2010 and the RDG4 (2011). By the way - you should be using the 2011 RDG, not the 2004! I don't have the 2004 RDG with me nor my original worked-out solutions. But I recall having the same comment as you. When I look at my 2011 RDG Table 3-1 pg 3-3, I too see the provided info results in a CZ of 38' to 46'. So, I agree that the minimum distance from edge of shoulder to obstruction should be 38' - 8' = 30'. I do not see 30' as answer (18, 26, 38, 46). Of the given choices, in my opinion, the answer would be C 38'. The solution in my PDF exam calcs out 38' but then labels the answer as D (46'). Also, there is another typo in the solution where 46 mph should be 46 ft. Unless someone else has any input (civilized?), I'd say the true answer would be 30' and the "best" answer would have to be C 38'.

 

[Peele1]

Is that a real freeway, or a rural highway? I ask because in WV, many roads have about 3" of shoulder before a rock wall, or drop off.

Example:

https://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=22102&aq=&sll=37.0625,-95.677068&sspn=63.343847,135.263672&ie=UTF8&hq=&hnear=McLean,+Virginia+22102&z=13&layer=t

 

[Predgw]

Ptatohed

My mistake, 4th edition, 2011 RDG. My Goswami print date is 2012 but it is clearly the same question as yours. Same answer choices. I think it is an error. The answer in the solutions states the Cz is 46' That is incorrect. The question ask for Minimum clear zone and the RDG gives guide. It is not economical to add 8 extra feet in some areas.

If this were an actually test question, I would have still got it correct because I would have selected C. 38'

Peele

It is stated as a rural freeway. In New England we have several areas where ledge in the median is not even close to the Cz requirements. The RDG does discuss the economics of obstruction removal, however I have never understood the decision to leave some of teh ledge I have seen. Very sad to see a cross near the rocks from time to time.

Thanks

 

[ptatohed]

Is that a real freeway, or a rural highway? I ask because in WV, many roads have about 3" of shoulder before a rock wall, or drop off.

Example:

https://maps.google.com/maps?f=q&source=s_q&hl=en&geocode=&q=22102&aq=&sll=37.0625,-95.677068&sspn=63.343847,135.263672&ie=UTF8&hq=&hnear=McLean,+Virginia+22102&z=13&layer=t

The problem statement states 2 lane rural freeway. The problem statement and diagram show no wall or drop-off, only a 4:1 slope from shoulder EP sloping toward a tree.

 

[ptatohed]

Ptatohed

My mistake, 4th edition, 2011 RDG. My Goswami print date is 2012 but it is clearly the same question as yours. Same answer choices. I think it is an error. The answer in the solutions states the Cz is 46' That is incorrect. The question ask for Minimum clear zone and the RDG gives guide. It is not economical to add 8 extra feet in some areas.

If this were an actually test question, I would have still got it correct because I would have selected C. 38'

It's probably a mistake but keep in mind when Goswami wrote this question, he was using the 3rd edition RDG. I doubt the RDG CZ table changed much between editions, if at all, but I'll check the 3rd edition when I get home. However, I do think I remember this discrepancy when I was studying, using the RDG3.

 

[civilized_naah]

Ptatohed

My mistake, 4th edition, 2011 RDG. My Goswami print date is 2012 but it is clearly the same question as yours. Same answer choices. I think it is an error. The answer in the solutions states the Cz is 46' That is incorrect. The question ask for Minimum clear zone and the RDG gives guide. It is not economical to add 8 extra feet in some areas.

If this were an actually test question, I would have still got it correct because I would have selected C. 38'

It's probably a mistake but keep in mind when Goswami wrote this question, he was using the 3rd edition RDG. I doubt the RDG CZ table changed much between editions, if at all, but I'll check the 3rd edition when I get home. However, I do think I remember this discrepancy when I was studying, using the RDG3.

I do not have the documents in front of me (traveling), but isn't the range of 38-46 ft for a corresponding range of foreslopes 1:5 to 1:4. In that case, shouldn't the high value 46 ft correspond to the steeper slope (1:4) and the low value correspond to the flatter slope (1:5)?

Or, in the words of Roger Clemens, I could be 'misremembering'

 

[ptatohed]

Ptatohed

My mistake, 4th edition, 2011 RDG. My Goswami print date is 2012 but it is clearly the same question as yours. Same answer choices. I think it is an error. The answer in the solutions states the Cz is 46' That is incorrect. The question ask for Minimum clear zone and the RDG gives guide. It is not economical to add 8 extra feet in some areas.

If this were an actually test question, I would have still got it correct because I would have selected C. 38'

It's probably a mistake but keep in mind when Goswami wrote this question, he was using the 3rd edition RDG. I doubt the RDG CZ table changed much between editions, if at all, but I'll check the 3rd edition when I get home. However, I do think I remember this discrepancy when I was studying, using the RDG3.

I do not have the documents in front of me (traveling), but isn't the range of 38-46 ft for a corresponding range of foreslopes 1:5 to 1:4. In that case, shouldn't the high value 46 ft correspond to the steeper slope (1:4) and the low value correspond to the flatter slope (1:5)?

Or, in the words of Roger Clemens, I could be 'misremembering'

I see your logic but that's not how I understand Table 3.1 to be read. When they say a foreslope of "1V:5H TO 1V:4H" correlates to a CZ of "38' TO 46' ", they don't mean a 1:5 slope should have a 38' CZ and a 1:4 slope should have a 46' CZ. They just mean if your slope falls anywhere from 1:5 to 1:4 your CZ should be anywhere between 38' to 46'. Actually, the more I think about it, the more your logic makes sense and it would actually be completely consistent with the old 2006 RDG3's Figure 3.1 graph. I think Fig 3.1 was eliminated from the 2011 RDG4 however (I'm at home now and I have RDG3 here and RDG4 at work). But, I am still pretty sure the intended way to read the table is "a foreslope range of this to that should have a clear zone of this to that". This can be confirmed by the examples at the back of the chapter. The RDG will provide you with the ADT, DS, slope and then state the CZ range from Table 3.1.

So, in problem 518, the minimum CZ would be 38' (of an available range of 38' to 46'). 38' - 8' shoulder = 30' (not one of the given answers).