Traffic signals are an essential, cost-effective tool to manage the movement of traffic and provide solutions to a variety of mobility, safety, and system management goals. However, traffic signals are sometimes an unnecessary expense that can add to collisions, congestion, and delay.
Key characteristics
Strategy description
Signalization and signal alternatives are the primary tools to manage traffic at intersections. For high volume and congested streets, signal timing strategies can help increase travel speed, reduce stop-and-go traffic, and increase the capacity at an intersection.
However, when considering traffic control strategies, it is necessary to consider the location, objectives for traffic operations on the street or corridor, and all available alternatives, including roundabouts and stop signs. Choosing which strategies make the most sense will depend on the transportation network, local traffic characteristics, and the objectives for the street or corridor.
Signalization options:
Signalization strategies range in complexity, involving varying degrees of technology and institutional cooperation. More highly optimized and responsive signal systems require greater investments in signal technology, traffic detection devices, communications equipment, and staff resources to operate and maintain the signal system.
Common signalization strategies include:
- Isolated signals that operate on a fixed schedule
- Actuated signals that use local traffic detection to initiate signal changes
- Coordinated signals that are optimized periodically using historical traffic patterns and traffic modeling for certain times of the day
- Coordinated signals that are proactively reviewed and optimized using extensive detection and performance reporting to continually adjust and improve optimizations as traffic conditions change
- Adaptive signals that use algorithms and real-time detection data to automatically adjust traffic signal timings in response to current traffic patterns
Alternatives to signalization:
After assessing the conditions and objectives of an intersection or corridor, a signal might not be needed. Consider non-signal traffic control alternatives where traffic volumes and speeds are low, where you observe safety, mobility, or operational concerns, or when traffic patterns or demand changes.
Common signal alternatives are:
- Roundabouts to allow the slow, continuous movement of traffic around a center island, without the need for traffic signals or associated technologies
- Stop signs that provide the lowest cost means to manage low traffic volumes and improve the safety of pedestrians and bicyclists
A less common signal alternative is the concept of shared space, in which road demarcations and traffic control devices are removed completely from the road. The goal is to lower vehicle speeds, increase driver awareness, and encourage person-to-person interactions to improve safety.
When to use this strategy
Signalization and signalization enhancements make sense when:
- Traffic volumes are high or anticipated to grow
- Traffic patterns are variable or unpredictable
- Traffic characteristics have changed, e.g., as a result of new residential or commercial developments
- A construction project requiring lane closures or traffic detours has caused a change in roadway capacity or demand
Benefits of introducing signalization or enhancing existing signalization strategies include:
- Increased travel speed
- Reduced stop-and-go traffic
- Increased capacity at the intersection
Signal removal or reconfiguration makes sense when:
- Traffic volumes and speeds are low-to-moderate
- Frequent collisions have been observed at the existing signalized intersection
- Sufficient space is available or can be obtained to convert to a roundabout
- Studies of the intersection have indicated that a traffic signal may not be necessary
Signal alternatives can also help address safety, congestion, maintenance, and environmental concerns:
- Removing unnecessary signals can reduce driver frustration, improve signal compliance, and can also reduce the frequency of head-on collisions
- Removal may reduce the use of alternate routes that lead to congestion in local areas
- Signal alternatives have lower initial costs and operations & maintenance costs because there are no traffic signals and associated equipment to maintain
- They can lower emissions by reducing stop-start conditions and persistent idling
What you need in order to implement
To install or use signalization, you will need to consider needs from policy-making to technical skills.
Policy needs:
- Policy decisions about system capabilities, data collection, system operation, and signal equipment
- Regular funding for signal timing review, multi-agency agreements, and policies where roadways cross jurisdictional boundaries
Planning needs:
- Before designing new signal strategies, the agency needs to understand the objectives for the street
- Obtain existing conditions information, including the number of vehicles, pedestrians, and bicyclists using each intersection
- To design optimized traffic signal timings, the designer will need to use a specialized software program to plan how traffic signals work together along the designated route.
Equipment needs:
- Vehicle sensors that measure the traffic conditions, and detect pedestrians, bicyclists, buses, and emergency vehicles
- Intersection traffic signal controller that runs the traffic signal timings
- Master traffic signal controller (optional) that communicates with each intersection traffic signal controller. The master traffic signal controller sets the current time-of-day and tells the intersection traffic signal controllers what optimized plan to run. One master traffic signal controller is needed for each group of optimized intersections.
- Central signal system software that monitors the status of each intersection traffic signal and can upload or download new optimized traffic signal timings
- Communications equipment between each intersection so the traffic signals can talk to the master traffic signal controller or central signal system
Maintenance needs:
- Regular updating of traffic signal timings based on changing traffic conditions, construction-related modifications to an intersection layout, changes to policies or signal timing standards, or temporary construction activities
Engineering resources and technical skills needs:
- Optimizing traffic signal timings typically requires an engineer using a software program to design the new signal timings, including the cycle lengths, splits, and offsets
These are the considerations for signal removal and alternatives:
Policy needs:
- Policies related to safety analysis and treatment implementation, pedestrian and bicycle considerations, and speed management that provide the backing for agencies to implement signal alternative and signal removal solutions
Planning needs:
- Clearly defined process for the planning, evaluation, and implementation of signal alternatives, both in residential neighborhoods and commercial business districts
- For complex signal alternative projects that require property purchases and/or new pavement, the project will need to go through a typical planning process that includes public feedback and environmental study
- Space feasibility analysis to confirm right-of-way requirements and potential obstructions
- Traffic demand analysis, including demand patterns, vehicle types, approach volumes, speeds, delay, crash history, and pedestrian and bicycle usage
Coordination needs:
- Coordination among traffic engineers, safety professionals, pedestrian and bicycle advocates, and adjacent property owners (residential and business) to ensure that their concerns around access and safe operation are acknowledged and addressed
- Coordination with emergency response and transit agencies to ensure that signal alternatives strategies accommodate specialized vehicles
Equipment needs:
- Basic traffic engineering tools: signing, striping, and equipment to construct signal alternatives
Maintenance Needs:
- Regular maintenance of signing and striping, including sign inspections and replacement as needed
- Normal maintenance that includes addressing roadway issues like potholes, restriping the lane markings, and sign upkeep
Agency resources needs:
- Funding for roadway treatments and experts to analyze where signal alternatives will be the most successful
- Staff to plan, design, construct, and maintain the signal alternative, or funding to hire outside of the Agency for one or more of these services
Learn more about this strategy
U.S. Department of Transportation Signal Timing Manual (PDF).
http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_812.pdf
National Cooperative Highway Research Program’s Report 572, Roundabouts in the United States (PDF).
http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_572.pdf
Federal HighwaysAdministration (FHWA), Roundabouts and Mini Roundabouts website.
http://safety.fhwa.dot.gov/intersection/innovative/roundabouts/
Federal Highways Administration (FHWA), Road Diet Resources website.
https://safety.fhwa.dot.gov/road_diets/resources/
Federal Highways Administration (FHWA), Road Diet Informational Guide, FHWA-SA-14-028, Washington, DC, 2014.
https://safety.fhwa.dot.gov/road_diets/guidance/info_guide/index.cfm
About key characteristics
Location notes:
Signalization strategies are appropriate for all locations where traffic volumes are high or anticipated to grow. Signal alternatives or removal strategies are appropriate for all locations where traffic volumes and speeds are low-to-moderate or where collisions are frequent.
Cost notes:
Costs to add or enhance signalization varies based on the extent of existing infrastructure, including signals, signal controllers, communications networks, and traffic detectors. Costs for signal alternatives also varies, depending on whether roadway reconstruction is required.
Technology notes:
Technology needs for signalization strategies vary depending on the sophistication of the strategy, but typically require signal controllers, communications networks, and traffic detectors. Signal alternatives operates without the need for traffic signals, which removes the need for these associated technologies.
Collaboration notes:
Signalization strategies are typically implemented on corridors that are within one agency’s boundaries and require minimal collaboration. More advanced signalization strategies that involve coordinated timing with traffic signals owned by neighboring agencies require additional collaboration with these agencies. Signal alternative or removal strategies require collaboration with local officials, community groups, and the public when planning and implementing the strategies to address potential access and safety concerns.