Have you ever experienced the case when arriving at a stop light, you see no other vehicle in the vicinity but you have to wait for the “normal” signal cycle? Have you ever been on a major surface street with a green light ahead, only to see the light cycle change to red upon your approach, with no one present on the cross streets? What a waste! And how about the occasions when you drive down a major urban arterial and catch stop light after stop light at each intersection? It seems like a waste of time, a waste of fuel, and an unnecessary burden on the environment. Isn’t there a better way?
According to a 2008 Texas Transportation Institute report, more than $87 billion and more than 4 billion h are wasted per year due to inefficient transportation networks. The solution is not to add more lanes; there simply is not enough land or money to do so. Instead, the focus should be on making the transportation system more efficient.
Several techniques are currently in place, including ramp metering, travel time websites, and actuated intersections. The U.S. Department of Transportation has initiated a substantial ITS (intelligent transportation systems) research program called IntelliDrive based on the belief that connectivity (vehicle to vehicles as well as vehicle to infrastructure) will improve the current situation further. The connectivity solution can provide localized and network-wide information, allowing transportation engineers to optimize traffic flow and efficiency.
The recent interest in IntelliDrive and vehicle connectivity has gone past previous notions of automatic collision notification, Internet browsing, and off-board navigation. Now, in addition to applying the 5.9 GHz ITS band for cooperative collision avoidance, other applications using connectivity between the vehicle and signalized intersections have emerged.
A group of researchers at Denso is investigating a number of ideas, including red light preemption and green light extension at individual signal-controlled intersections and along urban arterials. One of the researchers was slated to present a paper on their ideas at the SAE 2010 Convergence conference in Detroit Oct. 19-20. According to the paper, the best way to optimize traffic efficiency is to provide the control mechanisms with the most accurate and timely information possible. It’s not essential to have a central traffic control system in place—in some large networks, that would not be optimum, in fact.
These two solutions would use IntelliDrive connectivity to communicate full BSM (Basic Safety Message) information to the signal controller, updated not just once but at a 5- or 10-Hz rate. This approach would provide data not only about how many cars are approaching in which lane, but also whether they are accelerating, braking, and/or planning to turn (using vehicle dynamics and state). Data can also be gained about vehicle type. Vehicle type is important in cases such as when two fully loaded semi-tractor trailers are in a left-hand queue lane; they require longer intersection clearance times than a passenger car.
Red light preemption would use much of the system functionality that already would be in place for IntelliDrive-based V2X safety applications, including accurate vehicular positioning, two-way wireless message exchange, and coordination between roadside traffic control and the vehicle.
Today’s actuated intersections can already provide many elements of the fundamental functions of the preemption application concept. At traffic-actuated intersections, the signal timing changes from cycle to cycle depending on the detected approach of vehicular or pedestrian traffic. Cycle times and green extension times are most often predetermined by models for intersection throughput (e.g., the Minimum Delay Model and the Hybrid Model). What Denso researchers propose is to adapt the appropriate cycle times and extensions to achieve the “state optimum.” This concept provides the opportunity to modify traffic control parameters based not on average but instantaneous flow data obtained from oncoming vehicle (later, pedestrians, bicycles, motorcycles, etc.) broadcast messages. IntelliDrive data could be used either alone or in combination with other more traditional sensors in actuated intersection equipment and accommodate short-term fluctuations in traffic flow.
Envisioned is utilization of IntelliDrive 5.9-GHz based WAVE/DSRC communications systems to transfer data about the vehicles to the intersection controller through the Road Side Equipment (RSE). In the system described, only a single simple intersection model with a fully actuated controller is contemplated; there is only one approach from each of four directions at a perpendicular intersection with a single red, yellow, green signal matched to each approach. Of course, much more elaborate intersections and controller programming is possible, but the idea is to begin to understand how such simple systems interact and affect driver behavior before moving on to more complex situations.
Red light preemption and green light extension applications for both vehicle onboard equipment and roadside equipment have been successfully implemented and tested in a controlled environment at Denso’s Vista, CA, facility.
This article is based on SAE technical paper 2010-01-2317 by Roger Berg of Denso International America Inc.