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Last updated on 2024年7月24日

How do you balance competing objectives and trade-offs in signal design and operation?

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Signal design and operation is a complex and dynamic process that involves balancing competing objectives and trade-offs among various stakeholders, such as drivers, pedestrians, cyclists, transit users, and emergency vehicles. How do you achieve optimal signal performance and efficiency while meeting the needs and expectations of different road users and minimizing negative impacts on safety, environment, and equity? In this article, we will explore some of the key challenges and strategies for signal design and operation in the context of traffic engineering.

本文章的要点总结

Systematic, data-driven approach:

Start with a clear definition of signal objectives and performance measures, then optimize timings for smooth traffic flow. Continual evaluation and adjustment ensure the signals meet changing needs effectively.
Consider spatial constraints:

Be mindful of existing physical features when designing signals. Compromises might be necessary, but safety and standards compliance are paramount for efficient and secure road operations.

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Paul G.

Executive | Leadership | Global |…
Alistair Gollop FIHE MIET

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1 Signal objectives and performance measures

One of the first steps in signal design and operation is to define the objectives and performance measures for the signal system. Objectives are the desired outcomes or goals that the signal system should achieve, such as reducing delay, improving safety, or enhancing mobility. Performance measures are the quantitative or qualitative indicators that evaluate how well the signal system meets the objectives, such as travel time, queue length, level of service, or crash frequency. Depending on the context and scope of the signal project, different objectives and performance measures may be prioritized or weighted differently.

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Paul G.

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Another aspect must be not to follow norms! Many companies simply copy the set up from another junction - when there are much more effective and efficient ways of operating intersections. It’s hard to break down what someone teaches you - just because “that’s the way we do it round here!” As Engineers we must strive to be the best (against the objectives) and deliver the best for society and be held accountable for what we deliver.

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2 Signal optimization and coordination

Another step in signal design and operation is to optimize and coordinate the signal timings and phasing to achieve the best possible performance for the signal system. Optimization is the process of finding the optimal values for the signal parameters, such as cycle length, green split, offset, and clearance intervals, that minimize or maximize a certain performance measure or objective function. Coordination is the process of synchronizing the signal timings along a corridor or network to create smooth and efficient traffic flow and reduce stops and delays. Optimization and coordination can be done using various methods and tools, such as analytical models, simulation software, or adaptive control systems.

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Paul G.

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It is important to not the wider impact of network changes on optimization. Whilst the focus is on junction queue/delay the overall network performance sometimes gets forgotten and can have far greater benefits. In addition, a minor change on an adjacent intersection, not on a corridor can have a significant impact too. Being aware of the sinks/sources at all times is crucial to achieving your objectives/goals.

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3 Signal trade-offs and constraints

However, signal optimization and coordination are not always straightforward or simple, as they often involve trade-offs and constraints among different objectives and performance measures. For example, reducing delay for one direction or mode of traffic may increase delay for another direction or mode of traffic. Increasing green time for one phase may reduce green time for another phase. Synchronizing signals for one speed may create platoons or gaps for another speed. Moreover, signal design and operation are subject to various physical, operational, and institutional constraints, such as intersection geometry, traffic demand, signal hardware, signal standards, and stakeholder preferences.

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Alistair Gollop FIHE MIET

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One area of constraint not mentioned is spatially. In many locations, the presence of existing features around a junction, such as buildings, public and private land, can have a serious impact on the ability of designers to optimise the geometric layout of a site to achieve the best levels of safety and efficiency. In addition, the existence of pipes and cables in the road and footway can conflict with the desired locations for traffic signal poles or other equipment. I have had a number of occasions over the years, where these types of issues have meant that it hasn't been possible to proceed with a project. A level of pragmatism is required, but as a safety system, we need to comply with relevant statutory and standards requirements.

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Lj Barnachea

Technical Project Consultant at iFERN Enterprise
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In addtion to the physical constraints mentioned aboved is the road users and vehicle types. Each vehicle type have different, acceleration, speed, turning space that is crucial to decision making of the control system on wether to terminate the phase/stage or extend. There are some areas where majority of the vehicles are cargo trucks that need more time to start from full stop to moving with slow accceleration. This will cause a mismatch from the preset (normally used) parameters in the signal controller. Therefore, a need for assessments and adjustment of some space/time measuring parameters must be considered aside from green and clearance times and phasing sequence.

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4 Signal evaluation and improvement

Therefore, signal design and operation require constant evaluation and improvement to balance the competing objectives and trade-offs and to adapt to changing traffic conditions and needs. Evaluation is the process of measuring and assessing the actual performance and impacts of the signal system using various data sources and methods, such as field observations, traffic counts, travel time surveys, or crash reports. Improvement is the process of identifying and implementing potential changes or enhancements to the signal system based on the evaluation results and feedback, such as adjusting signal timings, modifying signal phasing, or upgrading signal equipment.

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Paul G.

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This is especially true when changes are made to the adjacent parts of the network or in planning. If a new school or super market/mall (as major attractors) are built, this can have a significant impact on O-D patterns and attractions not just locally but across the whole network and impact it undue it, despite best efforts. When changes are being discussed in planning, safety of other aspects of network operations - like major events, these all need careful consideration for the impact at a network level as well as corridor.

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5 Signal communication and collaboration

Finally, signal design and operation also require effective communication and collaboration among various stakeholders and partners involved in the signal system, such as traffic engineers, planners, operators, maintenance staff, enforcement officers, transit agencies, emergency services, utility companies, and road users. Communication is the process of sharing and exchanging information and knowledge about the signal system, such as signal objectives, performance measures, optimization methods, evaluation results, or improvement plans. Collaboration is the process of working together and coordinating actions and decisions about the signal system, such as setting priorities, resolving conflicts, allocating resources, or monitoring outcomes.

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6 Signal best practices and resources

To help you balance competing objectives and trade-offs in signal design and operation, here are some best practices and resources you can use. Start by following a systematic, data-driven approach for signal design and operation. This includes defining objectives and performance measures, optimizing and coordinating signal timings and phasing, evaluating and improving signal performance and impacts, and communicating with stakeholders and partners. Utilize reliable methods and tools for signal optimization and coordination that suit the context of your project, such as HCM, Synchro, TRANSYT, SCATS, or SCOOT. When optimizing and coordinating signals, consider the trade-offs among different objectives, such as delay, throughput, safety, environment, equity, or reliability. You may also want to use multi-objective optimization techniques or sensitivity analysis to explore different scenarios. Additionally, evaluate your signal system regularly using various data sources and methods. Establish clear roles and responsibilities when communicating with stakeholders and partners. Lastly, refer to available resources for guidance on signal design and operation.

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7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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How do you balance competing objectives and trade-offs in signal design and operation?

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1 Signal objectives and performance measures

2 Signal optimization and coordination

3 Signal trade-offs and constraints

4 Signal evaluation and improvement

5 Signal communication and collaboration

6 Signal best practices and resources

7 Here’s what else to consider

Traffic Engineering

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