Innovative Pre-Preemption Strategies for Traffic Light-Controlled Intersections Adjacent to Railroad Crossings

Navigating busy intersections near railroad crossings can be a significant challenge, especially during rush hour when trains roll through, causing traffic lights to change and cars to back up. But what if this chaos could be predicted and managed before it even begins? Enter pre-preemption strategies — an innovative approach designed to keep traffic flowing smoothly and safely, even when trains are on the move. This cutting-edge technology can transform how cities handle these tricky intersections, making commutes quicker and safer for everyone.

Traffic light-controlled intersections near crossings

Grade crossings necessitate that vehicles stop when a train passes. Nearly 40 percent of these crossings are situated in urban areas. These railroad crossings and adjacent intersections demand special attention, as vehicles must be halted to avoid collisions when a train approaches.

To address this, traffic lights are often installed at the intersections near these crossings. When a train is imminent, these traffic lights change to ensure all vehicles are safely stopped before the train arrives. However, the proximity of traffic lights to railroad crossings can complicate matters. If a train is approaching, the traffic light must halt vehicles not only at the crossing, but also at the nearby intersection, leading to potential backups and delays. Buses, in particular, can get delayed or even stuck at crossings or backed up onto nearby traffic light-controlled intersections, exacerbating the situation for public transit users. Effectively managing the flow of cars and trains in such scenarios requires careful planning to maintain smooth traffic movement and ensure safety for all road users.

Unique safety and mobility problems

Railroad crossings, particularly those near traffic lights, create unique challenges for traffic flow and safety. When a train nears a railroad crossing, traffic lights must change immediately to prevent vehicles from getting stuck on the tracks, which can result in severe crashes and incidents. Traditional traffic signal preemption strategies are used to manage this situation by overriding normal operations of traffic lights and providing green lights to vehicles approaching or passing tracks to clear the tracks.

However, these strategies often struggle with the complexities of contemporary traffic conditions, especially during rush hours. Heavy traffic can cause long backups from the railroad crossing to nearby intersections. This congestion not only increases the risk of vehicle-train collisions at the crossing or vehicle-vehicle crashes at the nearby intersection, but also worsens traffic delays, frustrating commuters and impacting local economies.

Understanding preemption

The Manual on Uniform Traffic Control Devices suggests using a preemption plan for traffic lights within 200 feet of railroad crossings to address these safety and mobility problems. This plan changes the traffic lights in a specific way to first clear vehicles off the tracks before a train arrives and then hold red lights for those vehicle movements towards the railroad crossing during the passage of the train. Preemption is a traffic management technique used to temporarily change normal traffic light operations to prioritize specific events and vehicle movements at the traffic light-controlled intersection adjacent to the crossing. While this helps improve safety, it does not completely solve the issue of heavy traffic jams at these intersections, especially during periods of heavy congestion.

Despite its effectiveness in clearing the tracks, regular preemption has limitations. During heavy traffic, it can create extensive backups at intersections, as the sudden traffic-light changes disrupt the normal flow of vehicles. Buses and other public transit vehicles can find themselves stuck at these intersections, further delaying schedules. This can lead to other issues, such as an increased risk of rear-end collisions and significant delays for motorists not directly affected by the railroad crossing.

The need for pre-preemption

The pre-preemption concept has been introduced to address the shortcomings of regular preemption. Pre-preemption aims to anticipate and manage traffic flow more proactively rather than reacting only when a train is near. The pre-preemption is a preemption. This involves preempting the traffic lights at intersections in advance of the regular preemption based on the detection of an approaching train much earlier along the track.

Pre-preemption aims to anticipate and manage traffic flow proactively, rather than reacting only when a train is near.

Pre-preemption relies on advanced train detection and communication systems between railroad and traffic light control systems. When a train is detected upstream, well before it reaches the railroad crossing or a train can securely communicate its location with the controller of the traffic light near the crossing one to two minutes in advance, the following actions can be initiated:

Early train detection and communication: Upstream train detection systems, such as track circuits or GPS-based technologies, identify an approaching train. This information is communicated to traffic light controllers at intersections adjacent to the railroad crossing.
Deployment of connected train technologies: Trains equipped with communication devices can send real-time data about their location and speed to roadside units, traffic management systems and traffic light controllers, allowing for more precise and timely signal timing adjustments.
Signal timing adjustment: Timings at traffic lights adjacent to the railroad crossing are adjusted before a regular preemption to manage and disperse traffic in advance. For example, traffic lights can be altered to allow more green time for traffic moving away from the railroad crossing, reducing the number of vehicles that might queue up on the tracks when the regular preemption takes place.
Dynamic traffic management: Smart systems use real-time data from traffic sensors to adjust traffic lights based on current conditions. This helps prevent long lines of cars and ensures smoother traffic flow. This action is optional but highly recommended.

How pre-preemption works to achieve dynamic traffic management.

Benefits of pre-preemption

Implementing pre-preemption strategies offers several key benefits, with enhanced safety being a primary advantage. By proactively managing traffic flow, pre-preemption reduces the risk of vehicles being caught on the tracks, thereby preventing potential train-vehicle collisions. This proactive approach significantly enhances safety at railroad crossings. Additionally, improved mobility is another critical benefit. Smoother traffic flow and reduced congestion lead to shorter travel times and less frustration for motorists, which is particularly important in urban areas where traffic delays can have significant economic impacts.

One of the notable benefits of pre-preemption is the positive impact on buses and public transit systems. By ensuring that buses do not get stuck at rail crossings or are not backed up onto nearby traffic light-controlled intersections, pre-preemption strategies enhance the safety of public transit, preventing potentially dangerous situations where buses could be hit by a train at the crossing or other vehicles at the nearby intersections. Additionally, pre-preemption helps maintain more predictable travel times for buses, which is crucial for public transit schedules. Fewer delays mean buses can adhere to their timetables more reliably, improving overall transit efficiency and passenger satisfaction.

Smart systems that adjust traffic lights based on real-time traffic data also help to achieve optimized intersection operations, enabling more efficient use of intersection capacity and accommodating fluctuating traffic volumes and train schedules. Furthermore, pre-preemption strategies contribute to reduced environmental impact. Smoother traffic flow means less idling and stop-and-go driving, which can lead to lower vehicle emissions and improved air quality, benefiting both the environment and public health.

Real-world implementation

Finding real-world examples of pre-preemption systems at traffic light-controlled intersections near rail crossings is challenging for a few key reasons. First, this is a relatively new and innovative technology so not many people know about it or understand how it works. Second, there has been limited effort to explore and integrate the necessary technology for detecting trains and communicating between roadside systems and traffic light controllers. Lastly, railroad companies often keep their train location data private due to safety concerns, which makes it harder to develop and implement these advanced pre-preemption systems effectively.

The Transportation Technology Center (TTC) in Pueblo, Colo., plays a crucial role in the development and testing of innovative transportation technologies. The center actively collaborates with researchers around the country to leverage expertise and resources to advance these technologies.

One upcoming collaboration will involve providing a venue for advancing the development of automatic traffic signal pre-preemption (ATSPP) systems. Researchers will use the TTC to test communication systems between trains and roadside units, evaluate connected train technologies and assess the performance of ATSPP systems. These efforts will include integrating connected train systems with traffic light controllers to develop a robust ATSPP system. Ultimately, this work aims to improve safety and mobility around railroad crossings and adjacent traffic light-controlled intersections, reduce crash risks and traffic congestion and lower vehicle emissions and vehicle fuel consumption.

Future direction and challenges

While pre-preemption presents a promising solution, several challenges must be addressed to ensure its widespread adoption and effectiveness:

Integration and compatibility: Ensuring seamless communication between railroad and traffic signal control systems is critical. This requires standardization and compatibility of technologies across different regions and jurisdictions.
Cost and funding: Implementing pre-preemption systems can be costly, involving significant investment in infrastructure and technology. Securing funding and demonstrating the cost-benefit ratio to stakeholders are essential for successful deployment.
Public awareness and education: Educating the public about the benefits of pre-preemption and how it works is important to gain community support and ensure compliance with traffic signal operations.
Continuous monitoring and adaptation: Traffic patterns and train schedules can change over time. Continuous monitoring and the ability to adapt signal timings and strategies are crucial for maintaining the effectiveness of pre-preemption systems.

Conclusion

Railroad crossings present complex safety and mobility challenges that require innovative solutions. By developing and adopting innovative pre-preemption strategies at a traffic light-controlled intersection near a railroad crossing, it is possible to enhance safety and mobility at the crossing and its adjacent intersections. Pre-preemption offers a proactive approach to managing traffic flow, reducing congestion and preventing train-vehicle and vehicle-vehicle collisions.

The integration of advanced detection and communication systems, real-time data and adaptive control algorithms is essential for the successful implementation of these traffic light pre-preemption strategies. The TTC plays a pivotal role in testing and refining these technologies, ensuring they are ready for deployment in diverse traffic environments.

As cities and transportation agencies continue to seek ways to improve safety and efficiency, the adoption of preemptive and pre-preemptive strategies represents a significant step forward. By working together, we can create safer, more efficient transportation systems that benefit everyone.

Innovative Pre-Preemption Strategies for Traffic Light-Controlled Intersections Adjacent to Railroad Crossings

Traffic light-controlled intersections near crossings

Unique safety and mobility problems

Understanding preemption

The need for pre-preemption

Benefits of pre-preemption

Real-world implementation

Future direction and challenges

Conclusion

Pei-Sung Lin, Ph.D., P.E., PTOE, FITE | Director of ITS, Traffic Operations and Safety Program

Zhenyu Wang, Ph.D. | Senior Research Faculty Member

Center for Urban Transportation Research

ENSCO Rail

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