Vehicular traffic analysis - PA
Hello,
Please can someone please clarify why answer B is the correct one? this is from the free NCARB PA exam
thank you!
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The shop is only open until noontime, so that immediately eliminates looking at the second diagram for 5pm. The shop has a drive thru on Main Blvd, so that narrows it to only looking at the numbers passing by A, B or C on Main Blvd (not 1st, 2nd, 3rd or 4th). Furthermore, because of median, you should only look at numbers on Main Blvd that occur on same side as the building. A has 258+100 turning from 1st=358.I assume we don't consider the 221 as additional because the number occurs downstream beyond the location of A. C has 97. I again assume we don't consider any of the upstream straight travel numbers because those occur at intersections before the building and thus could've turned onto side streets before reaching C. B has 597 (and per the official answer 54 additional coming from 3rd=651). I found the location of numbers on the plan ambiguous in meaning/relationship to the road segments and the methodology unclear. It seems we aren't supposed to figure out what numbers didn't turn upstream of C and instead trickled through going straight in addition to the 97?
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Hi Sean,
Thank you for your answer. I agree the numbers and arrows are quite confusing.
Thank you for pointing out we should only focus on the 8am diagram. I was in a rush when answering this question and didn't realise it was open till 12pm not 12am so i was looking at both diagrams actually.
Focusing only on the 8am diagram - perhaps the only numbers we should focus on are the ones that are on the same side of the building, when the arrow is straight and/or when the traffic is turning right not left?
A: 258
B: 597
C: 436 + 97 = 533
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Can someone help me understand the traffic analysis logic for this practice exam diagram? I’m confused about why we don't count the entire volume on Main Boulevard in the AM, and whether the Second Street traffic should be included. Is the business considered a corner lot, or does it only face Main Boulevard? I’d also love to find more practice diagrams exactly like this one, as it's the only example I’ve found so far. Where is the best place to study this specific topic?
Thanks! -
Hi Art,
Know that these traffic diagrams are not something that are likely to be a good use of your study time for the exam - one or two questions on PA or PPD at most, zero more often than not. Your time is better spent on sun path diagrams and reading topographic maps and that kind of thing - the knowledge for those topics will help you more on a lot more different kinds of questions.
The reason you don't sum up all the different counts on Main when checking the traffic count at each location is that the different counts are already cumulative - every car that passes each intersection is counted at that intersection. If you sum them, you count the same car more than once.
You might also be trying to count the traffic flowing in both directions - the question tells you no left turns, so you only want traffic on the right side of the road relative to your building site.
The question states the building has a drive-thru on Main Boulevard, you'd have additional info if it were a corner lot, or the site would be more clearly marked as a corner lot - you're reading things into the question that aren't really there. You don't double-count the Second-St traffic, but you do add the traffic from the side streets that is turning onto the right side of Main with the traffic continuing straight on Main from the previous intersection to get the accurate count of the number of cars passing the site.
There's a reason it's the only practice diagram you've found - it's the kind of rare oddball question included mostly to eat your time on the exam, so that you don't get to all the questions. Remember - you're not trying to get all the questions right, you're trying to pass - and every question is worth the same toward a passing score. You probably can Google "traffic diagram" or some related terms and find some more info about this kind of traffic study from a State DOT or similar source if you're really curious about them, but I'd move on to other topics for now.
Best,
Ralph, the Amber Book Team
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