NETTCP Traffic Management & Control Systems 4 — Questions and Answers
Question 1: A traffic engineer notices that vehicle queues from one intersection are blocking the stop bar of an upstream intersection. This condition is called:
- Spillback (Correct answer)
- Platooning
- Offset error
- Cycle failure
Correct answer: Spillback
Spillback occurs when downstream congestion causes queues to extend back and block upstream intersections, disrupting signal coordination.
Question 2: What is the purpose of an 'all-red' clearance interval at a traffic signal?
- Allow pedestrians to cross in all directions simultaneously
- Provide time for vehicles and pedestrians to clear the intersection before conflicting movements begin (Correct answer)
- Reset the controller to the beginning of the cycle
- Give emergency vehicles time to pass through the intersection
Correct answer: Provide time for vehicles and pedestrians to clear the intersection before conflicting movements begin
The all-red interval holds all approaches on red simultaneously, providing a safety buffer for vehicles that entered on late yellow to clear before cross traffic receives green.
Question 3: In ITS, a 'Video Incident Detection' (VID) system is designed to:
- Issue speeding tickets automatically to violators
- Automatically identify incidents such as stopped vehicles or wrong-way drivers using camera feeds (Correct answer)
- Replace human operators in a traffic management center entirely
- Control traffic signals based on pedestrian counts from video
Correct answer: Automatically identify incidents such as stopped vehicles or wrong-way drivers using camera feeds
VID algorithms analyze CCTV feeds to detect anomalies like stalled vehicles, debris, or wrong-way driving and alert operators.
Question 4: Which federal manual establishes uniform standards for traffic control devices including signs, signals, and pavement markings in the United States?
- AASHTO Green Book
- Manual on Uniform Traffic Control Devices (MUTCD) (Correct answer)
- Highway Capacity Manual (HCM)
- NACTO Urban Street Design Guide
Correct answer: Manual on Uniform Traffic Control Devices (MUTCD)
The MUTCD, published by FHWA, is the national standard governing the design, placement, and operation of all traffic control devices on public roads.
Question 5: What is 'traffic signal coordination' intended to achieve on an arterial?
- Reduce the number of signals needed on the corridor
- Create a 'green wave' so vehicles can travel through multiple signals without stopping (Correct answer)
- Increase the cycle length at every intersection to reduce conflicts
- Eliminate left-turn movements to simplify signal phasing
Correct answer: Create a 'green wave' so vehicles can travel through multiple signals without stopping
Coordination offsets green phases along a corridor so a platoon of vehicles traveling at the design speed encounters mostly green lights.
Question 6: When a signal controller operates in 'free' mode, it means:
- The signal is operating without any power
- The controller is running its own timing without synchronization to adjacent signals (Correct answer)
- Pedestrians can cross freely in all directions
- The controller is being programmed remotely by the TMC
Correct answer: The controller is running its own timing without synchronization to adjacent signals
Free mode means the controller operates independently on its local clock without a coordination reference signal, breaking the green wave.
Question 7: Transit Signal Priority (TSP) differs from emergency vehicle preemption in that TSP:
- Completely overrides the signal cycle and holds all other movements on red
- Makes minor adjustments like extending green or advancing the next green to help buses stay on schedule (Correct answer)
- Is only used at railroad grade crossings
- Requires manual activation by the signal operator at the TMC
Correct answer: Makes minor adjustments like extending green or advancing the next green to help buses stay on schedule
TSP makes conditional, non-disruptive adjustments to help transit vehicles without fully preempting normal signal operation.
NETTCP Traffic Management & Control Systems 4
A traffic engineer notices that vehicle queues from one intersection are blocking the stop bar of an upstream intersection.
This condition is called: