Min curb radius Question

Can somebody explain this problem, please

What is the difference between exh. 9-19 and 9-31 Green Book

Problem:

Have typ. 48' intersection (2 lane (12') each direction).

No shoulder or parking lines

Simple curb radius (no tapers)

WB-50 design vh.

Question:

Considering multiple maneuvering types, the minimum curb radius needed to prevent encroachment into the opposite lanes for the given vehicle is most nearly:

A) 50 ft

B) 30 ft

C) 20 ft

D) 40 ft

Answer: (which I can't accept or understand)

Using Exh. 9-31, pg 615 of the Green Book - need both maneuvering types to be < or = ft (with of two lanes)

This requires the curb radius R= 40 ft (answer D)

A20, look at Exh 9-31. You know (or at least can safely assume) the Angle of Intersection is 90^, right? And you know you have a WB-50 Design Vehicle (given). Now, you need to go across until you find the data that satisfies your criteria. We know that d2 needs to be 24' maximum (the truck may use the two 12' lanes in his direction but may not use any of the opposing lanes). But, the problem statement did not tell us if we have a case A or B. So we need to find a solution that satisfies either case. Per the exh, the only radius that satisfies that both A and B are less than or equal to 24' is R=40' (A: d2 = 22', B:d2 = 18'). Does that make sense?

Case A will govern since it requires a larger turning radius. For instance, if we knew that in the above problem we had a case B, our curb radius can be as small as R = 15' (B:d2 = 22')

Platohed,

thanks, it does make sense. that is probably the only answer to this problem. Do you know in what case should I use tbl.9-19. Can't figure out the difference between tables. Actually, do you think, if radius is not given in tbl.9-19, I should go to to tbl. 9-31. Or its a different case

Ambrug20 said:

Platohed,

thanks, it does make sense. that is probably the only answer to this problem. Do you know in what case should I use tbl.9-19. Can't figure out the difference between tables. Actually, do you think, if radius is not given in tbl.9-19, I should go to to tbl. 9-31. Or its a different case

Click to expand...

Well, the problem statement said 'simple curb radius (no tapers)'. Exh 9-19 incudes tapered turns. Exh 9-31 does not include tapers. The idea behind Exh 9-19 is that tapers are included near the inner travel way edge right turn radius so that a (larger) turning vehicle does not leave its lane. For a graphical representation of a WB-50 making a right turn at a tapered edge of travel way, see Exh 9-24, pg 600. I hope that helps. Did I answer your question?

Platohed,

thanks for the detail and logical explanation. i would never understood this table and nobody could explain it better that you did. I assume you are planning to take Transportation this Friday. If it is, good luck to you. You seems very well prepared and smart enough to pass it. :reading:

I have been trying few times, know a lot of stuff, but can't brake this wall for some reason. Will try this time again. :tardbang:

Ambrug20 said:

Platohed,

thanks for the detail and logical explanation. i would never understood this table and nobody could explain it better that you did. I assume you are planning to take Transportation this Friday. If it is, good luck to you. You seems very well prepared and smart enough to pass it. :reading:

I have been trying few times, know a lot of stuff, but can't brake this wall for some reason. Will try this time again. :tardbang:

Click to expand...

My pleasure A20. FYI - I passed 8-hr/Transpo in April 2011. Best of luck to you this Fri.