lec 27: ch3.(t&ld): traffic analysis – directional distribution of site traffic
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Lec 27: Ch3.(T&LD): Traffic Analysis – Directional distribution of site traffic. Notice the difference in the trip distribution process between urban transportation planning and site planning Understand several factors affect directional distribution of site-generated traffic - PowerPoint PPT PresentationTRANSCRIPT
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Lec 27: Ch3.(T&LD): Traffic Analysis – Directional distribution of site traffic
Notice the difference in the trip distribution process between urban transportation planning and site planning
Understand several factors affect directional distribution of site-generated traffic
Be familiar with methods used to distribute site traffic to surrounding roads
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Directional distribution of site traffic The assumptions and method used in estimating the
direction in which traffic will approach and depart the site will vary with several location-specific conditions, such as;
Size of the proposed development
Type of development (e.g. industrial, commercial, residential, etc.)
Prevailing conditions on the existing street systems
Available data base
Avoid evaluating TIA based on “mechanical method” A very good warning from the authors. Choose a method appropriate for the situation rather than using a canned procedure. (P.49)
Primary market
Analogy
OD (easy said, hard done)
Gravity method (we did this already.)
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Primary market The primary market (area-of-influence) method
utilizes a unique trade area or area of influence. It is the geographical area from which a high percentage (80%) of the site-generated traffic will be “drawn” to the site.The boundary of the trade area might be identified by one of the following techniques:
Method 1: Delineate the trade area as a regular geometric shape (a circle or square with the site at the center) with a radius of travel appropriate for the type of development
Method 2: Delineate the trade area by establishing the most distant points that can be reached within some selected travel time over the specific street system
Method 3: Use Reilly’s Law of Retail Gravitation to establish the boundary between competing centers
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Maximum travel times (how far people travel?)
Community shopping center: 15-20 min
Neighborhood shopping: 10 min
Industrial park: 30 min
Residential: peak-hour = 30 min; Other = 20 min
Travel time (not distance) and trip purposes are the determinants of trip length.
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Method 1: Defining the study area
Step 1: Select the appropriate max trip length for the study site
Step 2: Draw the selected geometric shape (a circle or a rectangle) with the center located over the site
(Steps 2 & 3)
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Method 1: Defining the study area (cont)
Step 3: Divide the trade area into sections (zones) and determine the amount of activity in each.
Step 4: Calculate the proportion of each section (zone) as a percentage of the total primary market area
(Step 4)
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Method 1: Defining the study area (cont)
Step 5: Identify the most logical route from the centroid of each section (zone) to the site.
Step 6: Calculate the directional distribution by assigning the percentage from step 4 to the minimum paths identified in step 5.
(Step 5)
34%, not 14%
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Method 2
This method uses the travel distance calculated along each route using the appropriate maximum travel time and the travel speed(s) on each street. Results in an irregular geometric shape. Steps 1 and 2. Travel time = say 10 min. Speeds on routes are different resulting in different distances.
Steps 3 through 6 are the same as Steps 3 through 6 of Method 1.
(Hah!? No shape shown!)
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Method 3: Reilly’s Law of Retail Gravitation (used when competing markets exist)
Reilly’s law:
A
B
ABA
PP
dd
1
A’s market boundary
PA PB
dAB
dA
A B
Pi: size of center I, commonly measured in 1000 sq. ft. of gross leasable area
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Method 3: Reilly’s method (used when competing markets exist) (cont)
(See page 53 for an example)
15 min
14 min
11 min
Once the boundary is defined, the rest is like step 3 though 6 of Method 1.
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Analogy (p.54) Identify existing situations which have the “same”
characteristics as expected of the subject. A traffic survey of a similar development in close proximity to the subject site follows this methodology.
In many cases, a manual count of turn movements is sufficient to obtain the necessary data for analysis of the direction of approach. With a large development where there are several approach streets, a license-plate survey might be used (find out how customers drive through the network to get to the site).
(See p.54 for possible applications)
Subject siteSimilar site
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Analogy (p.54) (cont): Example in p.54
Note that these two sites face the same Main St.
(Assumed site-traffic distribution)
(Turn movements used to determine traffic distribution)
Find out % distribution: from north or from south