Cooperative Adaptive Cruise Control (CACC) technology stands at the forefront of automotive innovation, promising to revolutionize driving by enhancing safety, traffic flow, and fuel efficiency. Unlike traditional Adaptive Cruise Control (ACC), CACC leverages vehicle-to-vehicle (V2V) communication to enable vehicles to dynamically adjust their speed and maintain closer following distances in platoons. This coordinated movement has the potential to significantly increase highway capacity and reduce traffic congestion. However, the successful implementation of CACC hinges not only on technological advancements but also critically on understanding and addressing human factors. This article delves into the key human factors research areas essential for the safe and effective deployment of CACC systems.
Willingness to Utilize CACC
The ultimate success of CACC technology is intrinsically linked to its acceptance and utilization by drivers. Despite the potential benefits, drivers may exhibit reluctance to adopt CACC, especially in scenarios where it could be most advantageous, such as dense traffic conditions. A primary concern revolves around drivers’ comfort levels with the automated system, particularly in situations demanding close vehicle proximity and reliance on technology for safe navigation.
Research Questions
Several critical questions need to be addressed to understand drivers’ willingness to utilize CACC:
- How does traffic density affect the choice to utilize CACC? (Traffic density) Understanding if drivers are less inclined to use CACC in heavy traffic, the very condition it’s designed to alleviate, is crucial.
- Does the number of travel lanes affect the choice to utilize CACC? (Available travel lanes) The complexity of multi-lane highways might influence drivers’ trust and willingness to engage CACC.
- Do available preset time-gap options affect utilization? (Time-gap options) The flexibility and range of time-gap settings offered by CACC systems could impact driver comfort and adoption rates.
- Does system reliability affect usage or complacency? (System failure rate, failure timing) Concerns about system malfunctions and the timing of failures can significantly shape driver trust and reliance on CACC over time.
Potential Methodologies
To explore these research questions, driving simulation offers a robust and safe environment.
- Driving simulation:
- Advantages: Driving simulators provide controlled environments to manipulate traffic scenarios and ensure participant safety.
- Disadvantages: The simulated nature might reduce the sense of real-world risk and realism in driver behavior.
- Resources: Mini-simulators or high-fidelity simulators can be employed based on research needs and fidelity requirements.
Workload, Situational Awareness, and Distraction
CACC systems are intended to reduce driver workload by automating speed and distance maintenance. This reduction in workload could free up cognitive resources, potentially allowing drivers to better focus on broader driving tasks like hazard perception. However, it also presents the risk of drivers diverting their attention to secondary, non-driving related tasks, which could negatively impact their situational awareness (SA) and ability to react promptly in critical situations.
Research Questions
The impact of CACC on workload, situational awareness, and distraction necessitates investigation through the following research questions:
- How does use of CACC affect workload and SA levels? (Automation) Quantifying the changes in driver workload and SA when using CACC is vital to understanding its cognitive effects.
- Are drivers more likely to engage in secondary tasks while utilizing CACC? (Automation) Assessing the propensity for drivers to engage in distracting activities when CACC is active is crucial for safety considerations.
- Do driving behavior and performance change during CACC driving? During secondary tasks? (Automation, secondary tasks) Examining how CACC and secondary tasks alter driving behavior and overall performance is essential for understanding potential risks.
- How quickly do drivers respond to events under manual and CACC driving? During secondary tasks? (Automation, event onset, secondary tasks) Measuring driver reaction times to unexpected events under different driving modes and distraction levels is paramount for safety analysis.
Potential Methodologies
Both driving simulation and field studies offer valuable approaches to investigate these aspects.
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Driving simulation:
- Advantages: Simulators offer controlled environments for introducing secondary tasks and measuring SA using specialized tools within scenarios, while maintaining safety.
- Disadvantages: Simulated secondary tasks may not fully replicate real-world distractions, and the realism of the driving experience remains a consideration.
- Resources: Mini-simulators or high-fidelity simulators, equipped with SA measurement tools.
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Field study:
- Advantages: Field studies provide real-world driving scenarios, enhancing ecological validity and realism.
- Disadvantages: Ensuring safety and controlling variables in real-world traffic environments pose significant challenges.
- Resources: Test tracks or controlled real-world environments are necessary for safe and ethical field studies.
Platoon Entry/Exit
CACC’s effectiveness relies on the formation and maintenance of vehicle platoons. However, entering and exiting these platoons presents unique challenges. The tight gaps within CACC platoons, while beneficial for traffic flow, can complicate merging for vehicles from adjacent lanes. Similarly, vehicles exiting a platoon need to manage their speed relative to both the platoon and surrounding traffic, potentially affecting platoon stability.
Figure 1. Illustration. Merging into a CACC platoon.
Figure 2. Illustration. Exiting a CACC platoon.
Research Questions
Understanding and optimizing platoon entry and exit maneuvers requires addressing the following research questions:
- How does a vehicle exiting a platoon affect traffic stability? (Speed of adjacent lane) Investigating the impact of platoon exits on the overall stability of the traffic flow, particularly concerning the speed of adjacent lanes, is crucial.
- Can V2V communications facilitate merges and improve performance? (Automation assistance) Exploring the potential of V2V communication to streamline merging and enhance the efficiency and safety of platoon operations is essential.
Potential Methodologies
Driving simulation and microsimulation offer complementary approaches to studying platoon dynamics.
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Driving simulation:
- Advantages: Simulators allow for the controlled study of merging scenarios and the implementation of simulated CACC assistance behaviors more easily than real-vehicle programming.
- Disadvantages: The realism of lane changes in simulators, particularly the limited rear-view perception, can be a constraint. Measuring large-scale stability effects may also be challenging.
- Resources: Mini-simulators or high-fidelity simulators are suitable for these investigations.
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Microsimulation:
- Advantages: Microsimulation excels in controlling platoon behavior and analyzing large-scale traffic flow effects.
- Disadvantages: Developing an accurate model that reflects real-world traffic behavior complexities can be difficult.
- Resources: Specialized modeling software is required for conducting microsimulations.
Arterial Intersections
The benefits of CACC extend beyond highways to arterial roads, particularly in approaching intersections. CACC-equipped vehicles, with access to traffic signal information, can optimize their speed to reduce unnecessary stops and starts, saving time and fuel. However, this optimized behavior can create challenges when interacting with non-CACC equipped vehicles, especially following vehicles that may not anticipate the deceleration for a red light.
Figure 3. Illustration. CACC-equipped vehicle followed by non-equipped vehicle.
Research Questions
The interaction between CACC and non-CACC vehicles at intersections raises several research questions:
- How does the following vehicle (participant) react to the lead vehicle slowing? (Deceleration rate) Understanding the reaction of drivers in non-CACC vehicles to the deceleration of a leading CACC vehicle is critical for safety.
- Does behavior change based on whether a red light is visible or not? (Visibility of intersection) The visibility of traffic signals might influence driver anticipation and reaction to CACC-induced deceleration.
- Does behavior change based on travel lane? (Travel lane) Lane positioning and traffic flow patterns might affect driver behavior in response to CACC vehicles at intersections.
- Does behavior change based on distance to the light when deceleration begins? (Distance to intersection at deceleration) The distance at which CACC initiates deceleration for a red light could impact the behavior of following drivers.
- Does behavior change based on environment (e.g., commercial, residential, or remote area) or traffic density? (Environment, traffic density) Environmental context and traffic density could modulate driver responses to CACC behavior at intersections.
Potential Methodologies
Driving simulation and naturalistic observation offer distinct advantages for studying intersection scenarios.
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Driving simulation:
- Advantages: Simulators allow for controlled manipulation of intersection scenarios and surrounding traffic, ensuring safety.
- Disadvantages: The clarity of distant objects like traffic signals might be a limitation in some simulators, although high-fidelity simulators can mitigate this. Potential lane changes in response to simulated scenarios might not fully reflect real-world behavior.
- Resources: Mini-simulators or potentially high-fidelity simulators, depending on the visual fidelity requirements.
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Naturalistic:
- Advantages: Naturalistic studies provide more realistic data by observing real-world driver behavior without intervention.
- Disadvantages: Controlling traffic conditions and signal phasing in naturalistic settings is challenging.
- Resources: Vehicles equipped with recording devices or teams of researchers for manual observation of following vehicle behavior in real traffic.
Carryover Effects
Extended use of CACC, which encourages closer following distances than typically deemed safe in manual driving, raises concerns about potential behavioral adaptation. Drivers accustomed to CACC’s shorter gaps might unconsciously carry over this behavior to manual driving, potentially increasing accident risks.
Research Questions
Investigating these potential carryover effects requires addressing the following:
- How closely do drivers follow a lead vehicle under manual control? Does this vary with speed? (Lead vehicle speed) Establishing baseline manual following distances at different speeds is essential for comparison.
- After periods of CACC usage, does the manual driving gap change? Does length of time under CACC control affect the manual gap? (Automation usage duration) Examining the impact of CACC usage duration on subsequent manual driving behavior is crucial for assessing carryover effects.
- Does traffic density affect following gap before or after CACC exposure? (Traffic density, automation exposure) Understanding how traffic density interacts with CACC exposure to influence following gaps is important for a comprehensive picture.
Potential Methodologies
Driving simulation is particularly well-suited for studying carryover effects in a controlled and safe manner.
- Driving simulation:
- Advantages: Simulators allow for controlled manipulation of CACC usage periods and subsequent manual driving scenarios while maintaining safety.
- Disadvantages: The inherent limitations of realism in driving simulators and the reduced perception of risk need to be considered.
- Resources: Mini-simulators or high-fidelity simulators are appropriate for these studies.
Following Vehicle Gap Comfort
While research has extensively explored drivers’ comfort levels with following distances, the comfort of being followed closely, especially at CACC-maintained gaps, remains less understood. Drivers might perceive close following by other vehicles as tailgating, especially if they are uncertain whether the following vehicle is also using automated systems. This discomfort could impact the acceptance and social dynamics of CACC implementation.
Figure 4. Illustration. Closely following vehicles in CACC platoon.
Research Questions
To address the issue of following vehicle gap comfort, the following research questions are pertinent:
- How comfortable is the participant with a following vehicle at short gap? (Time gaps) Quantifying drivers’ comfort levels with varying short following distances is essential.
- Does comfort level change after driving a CACC vehicle? (Experience with CACC) Investigating whether experience with CACC alters drivers’ comfort with being closely followed is crucial.
- Does comfort level change if the participant is the lead vehicle or part of a platoon? (Platoon position) Exploring how platoon position affects comfort with following distances is important for understanding platoon dynamics.
- Does comfort level change as density of surrounding traffic changes? (Traffic density) Traffic density might modulate drivers’ comfort with close following distances.
- Does comfort level change if the participant knows the following vehicle is manually driven or has CACC engaged? (Following vehicle mode) The perceived automation status of the following vehicle could significantly influence driver comfort.
If a positive effect of knowing the following vehicle is CACC-engaged is found, further research into the best methods for communicating this information to lead drivers, such as indicator lights or in-vehicle displays, would be warranted.
Potential Methodologies
Field studies and driving simulation both offer valuable approaches to investigate following vehicle gap comfort.
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Field study:
- Advantages: Field studies offer realism by allowing participants to experience real-world traffic and observe following vehicles directly. They provide more naturalistic data on driver comfort.
- Disadvantages: Controlling traffic density and ensuring safety with multiple CACC-equipped vehicles are significant challenges.
- Resources: Requires three or more CACC-equipped vehicles and a controlled test track environment.
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Driving simulation:
- Advantages: Simulators allow for easier control of surrounding traffic and the programming of CACC-equipped vehicles. Mini-simulators might be sufficient, reducing resource demands.
- Disadvantages: Simulators may not fully replicate the realism of the rear-view environment, as physical head movements for additional information are limited.
- Resources: Driving simulator facilities are necessary.
This exploration into human factors research areas underscores the critical importance of considering driver behavior, perception, and acceptance in the development and deployment of CACC technology. Addressing these research questions is crucial to ensure that CACC systems are not only technologically advanced but also safe, user-friendly, and effectively integrated into the complexities of real-world traffic environments.
