DSD vs SSD

[team1887]

I want to make sure my logic is correct in distinguishing one from the other, if its not specified in the exam.

I have a problem that asks for the sight distance in an urban area and a jogger appears out of no where. parked cars are on both sides, one 12ft lane road.

Initially I was going to use SSD to find this value, but it wasnt in the answer set. My logic there, was that SSD was also used for "unexpected obstacles".

But doing some more research (and looking at the solution to realized my initial reasoning was wrong) led me to believe that using DSD was a better choice since the drivers field of vision is "cluttered" by other things such as a fairly narrow roadway (no where to escape/swerve, change direction, etc) and parked cars on both sides of the road. So its not necessarily a decision that needs to be made in this case, but an unexpected maneuver that needs to occur.

And we wouldn't used maneuver E since there is pretty much no where to go expect straight. We have to come to a complete stop so we don't hit the jogger. So the right answer was using maneuver B for DSD is the correct sight distance required to not hit the jogger.

Is my logic right? did I miss something? Im not entirely sold on it. Thank you for your input.

 

[BLG923PE]

Could be wrong but I think all of the SD problems I did in the practice exam specified which one they wanted.

However, I also think the way the problem is written will give you clues. It stated urban and went to the trouble of hinting that an avoidance maneuver wasn't possible.

When it comes to real design, it is a judgement call in my opinion and I don't feel there is really any "rule".

 

[afraid]

I believe this is a problem from SOPE. They're using the most conservative approach. And like blg23 implied, if the information is there make the most of it. If information about the maneuvering wasn't available then your instincts would be correct. I know you heard this before "analyze each drop of ink ".

 

[ptatohed]

I want to make sure my logic is correct in distinguishing one from the other, if its not specified in the exam.

I have a problem that asks for the sight distance in an urban area and a jogger appears out of no where. parked cars are on both sides, one 12ft lane road.

Initially I was going to use SSD to find this value, but it wasnt in the answer set. My logic there, was that SSD was also used for "unexpected obstacles".

But doing some more research (and looking at the solution to realized my initial reasoning was wrong) led me to believe that using DSD was a better choice since the drivers field of vision is "cluttered" by other things such as a fairly narrow roadway (no where to escape/swerve, change direction, etc) and parked cars on both sides of the road. So its not necessarily a decision that needs to be made in this case, but an unexpected maneuver that needs to occur.

And we wouldn't used maneuver E since there is pretty much no where to go expect straight. We have to come to a complete stop so we don't hit the jogger. So the right answer was using maneuver B for DSD is the correct sight distance required to not hit the jogger.

Is my logic right? did I miss something? Im not entirely sold on it. Thank you for your input.

I agree with blg. Since the problem stated urban and hinted that no path or direction change is possible, then you know to use DSD, case B (stop on urban road). The SSD and DSD (cases A and B) formulas are the same, it's only the 't' that differs.

 

[team1887]

Thank you for confirming.