Lecture #7 Chapter 16: Principles of Intersection Signalization (cont.)

Objectives Understand concept of delay and how it relates to the traffic stream

Intersection Delay What are the different measures of delay? Roess, P. R., W. R. McShane, E. S. Prassas. Traffic Engineering. Prentice Hall

Intersection Delay What are the different components of delay? – Uniform Delay (UD)

Intersection Delay What are the different components of delay? – Random Delay (OD)

Intersection Delay How is signalized intersection delay modeled? – d = 0.90 [UD + RD]

Signal Cycle What cycle minimizes signalized intersection delay? C o =minimum delay cycle (sec) L=total lost time (sec) (v/s) c =saturation flow ratio for critical movement

Signal Cycle How sensitive is delay to cycle time? – ¾ C – 1 ½ C – Why is this significant to a traffic engineer?

Intersection Overflow Delay What would long term overflow look like?

Intersection Overflow Delay Are there any practical problems associated with the delay model?

Intersection Delay: Bridging the Gap There are a variety of delay models – Australian – TRANSYT – HCM (isolated intersection) Based on theoretical UD and OD Calibrated using X 2

Intersection Delay: Urban Signalized Intersections Does arrival at an intersection affect delay? – {link to Excel file} {link to Excel file}

Intersection Delay: An Approximation “No claim is made that the formulas are correct, but rather that they yield answers which do not violate elementary logic in the region of v/c near unity where neither the steady-state nor the oversaturation models can be expected to yield reasonable results.”

Intersection Delay Simulation How have these delay models been validated?

Intersection Stopped Delay Conversion What about the constant, 1.3, used to convert approach delay to stopped delay?

Intersection Delay Sample Calculations Given: – v = 1100 vph – s = 2000 vphg – C = 120 sec – g/C = 0.52 Find: – Average stopped delay for the first 15 minutes of the specified conditions

Conclusion New Homework Assignment: – Check web for HWK #3 Homework Assignment due: – Assignment #2 Lab Announcements – Data collection Monday, next week