4. DIRECTIONAL METHOD ITERATIVE PROCEDURE
PAGE 115, NCHRP REPORT 765
Utilized by web application
Input
1. Description of intersection turning movement patterns
• Actual traffic counts, or
• Estimate percent of vehicles leaving each lane of approach
2.Future year link volume forecasts
• Traffic model
Output
• Intersection turning movement volumes in future year
5. DIRECTIONAL METHOD ITERATIVE PROCEDURE
PAGE 115, NCHRP REPORT 765
Methodology (in a nutshell)
1. Convert future year link volumes into directional inflows, outflows
from intersection
2.Calculate initial estimate of turning movement volumes
3. Check if estimated approach outflows ≈ future year link outflows
‐ If not, re‐estimate turn volumes
4.Check if estimated approach inflows ≈ future year link inflows
‐ If not, re‐estimate turn volumes
5. Continue re‐estimating turn volumes until approach inflows,
outflows ≈ future year link inflows, outflows
6. TURN FLOWS OVERVIEW
Turn Flows
• Includes turn volume calculator, user
guide
• Calculator programmed with JavaScript,
accompanying website with HTML, CSS
Data Input
• Requires turning movement, future
volume information
• Entered through graphical user
interface (GUI; “gooey”)
• GUIs indicate type of number, units
• Multiple GUIs for different data
Turning Movement Input GUI
7. TURN FLOWS OVERVIEW
Errors
• User prevented from typing letters,
spaces, symbols (excluding periods)
as input
‐ Program cannot interpret # $ % @ ‘ spaces
or letters in mathematical operations
‐ Periods allowed so decimal numbers may
be used
• Accidents can still happen (missing input,
periods entered without numbers)
‐ If detected:
1. Error message displays onscreen
2. Future year turning volumes display as zero
Turn Flows Error Message
8. TURN FLOWS OVERVIEW
Results
• Click ‘Calculate’ button to run program
• Turning movement volumes display at
bottom of web page
Turn Flows Results Output
