Adaptive signals change traffic signal timings based on current traffic conditions. Using hardware, adaptive signals measure the traffic conditions of vehicles, bicyclists, and pedestrians and then utilize software to make timing changes based on the real-time data.
Key characteristics
Other names
- adaptive traffic signal control
- adaptive traffic control system
- adaptive signal timing
Strategy description
Adaptive signals use software to make timing changes to traffic signals in response to traffic conditions. Signal timing is calculated in real-time based on traffic demand and can adjust with each cycle. This software often requires a central system that analyzes traffic data and sends timing instructions to multiple traffic signals. Adaptive is the most advanced signal control technology available and requires reliable vehicle detection and communications equipment.
The importance of automated timing changes
Adaptive signals change without human interaction and automatically adjust the length of green time given to each movement at an intersection based on what the traffic conditions need. This enables the traffic signals to better serve all people (vehicles, pedestrians, bicyclists) moving through the intersection or along a roadway.
Coordinating traffic signals with a time-of-day schedule often provides benefit-cost ratios near 20:1. Using adaptive signals can reduce the number of times vehicles stop at traffic signals and the amount of time they wait at a red light by another 10% compared to traffic signals only coordinated on a schedule.
When to use this strategy
Adaptive signals work best at high-volume intersections that have variable or unpredictable traffic patterns and require multiple signal timing solutions.
Strategy benefits:
- Automatic response to changing traffic conditions
- Helps reduce congestion
- Reduces the amount of time vehicles have to wait at a red light, reducing fuel consumption and emissions
What you need in order to implement
At a high level, adaptive signals will require planning, equipment, maintenance, and technical skills.
Planning needs:
- Before implementing adaptive signals, agencies should use the systems engineering process to identify needs and requirements, and determine if adaptive signals are appropriate.
- Systems engineering is required for adaptive signals projects that are Federally funded.
Equipment needs:
- Vehicle sensors that calculate volumes in each lane
- Communications equipment between each intersection so the traffic signals can share data
- Some systems require communications connecting the traffic signals to a central server
- Common software at each traffic signal
Maintenance needs:
- Adaptive signals rely on the sensors to calculate the timings. Therefore, failed sensors must be repaired faster than non-adaptive signals.
- Adaptive signals rely on communications equipment to "talk" to other intersections. Therefore, failed communications must be repaired quickly.
Technical skills needs:
- Adaptive signals add complexity. Agencies must commit resources to program and operate adaptive signals.
Learn more about this strategy
Federal Highways Administration, (FHWA) resources:
FHWA Adaptive Signal Control Technology.
FHWA Adaptive Signal Control FAQs.
FHWA Adaptive Signal Control Brochure (PDF).
FHWA Model Systems Engineering Documents for Adaptive Signal Control Technology.
FHWA Systems Engineering Guidebook for Intelligent Transportation Systems (ITS).
About key characteristics
Cost notes:
Adaptive signals represent the highest cost of any signal coordination solution because it relies on a significant level of technology to measure the current traffic conditions and make timing decisions in real-time. It also requires dedicated staffing and funds to operate the system.
Technology notes:
Adaptive signals require reliable traffic detection and robust communications networks to share data between traffic signals and a central system. Without this detection and communications, they cannot operate properly.
Collaboration notes:
Adaptive traffic signals must use a common intersection software. In cases where the adaptive system makes decisions from a central server, then all intersections must also use a common central server software. Therefore, the level of collaboration is low when installed at intersections owned and operated by a single agency because they typically operate the same local intersection software. The level of collaboration is high when the adaptive signal system will be installed at intersections owned by multiple agencies because all agencies must agree to use the same intersection software. All agencies must also agree to use the same central server software when the adaptive system makes decisions from the central server.