Transportation Engineering: Traffic flow fundamentals — Flow, Speed and Density
How flow, speed and density define a traffic stream, why they trade off, and how engineers measure them on real roads.
Transportation Engineering · 23 questions
Try 3 questions
1. Which equation links traffic flow, density and speed?
- Speed = flow × density
- Density = flow × speed
- Flow = density × speed
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Answer: Flow = density × speed
Vehicles per hour equals vehicles per kilometer times kilometers per hour; this identity, q = k·v, is the foundation of traffic flow theory.
2. A lane holds 40 vehicles per kilometer moving at 50 km/h. What is its flow?
- 2,000 vehicles per hour
- 800 vehicles per hour
- 1,250 vehicles per hour
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Answer: 2,000 vehicles per hour
Flow is density times speed: 40 veh/km × 50 km/h = 2,000 veh/h.
3. What does traffic density measure?
- Average time between successive vehicles
- Vehicles passing a point each hour
- Vehicles per kilometer of lane at one instant
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Answer: Vehicles per kilometer of lane at one instant
Density is a snapshot in space: count the vehicles on a stretch of road at one moment and divide by its length. Flow, by contrast, is counted at a point over time.
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