Lane assist technology

Lane Assist Technology in Subaru Eyesight-enabled Vehicles Source: youtube

Introduction

Lane assist technology helps prevent car accidents caused when the driver unintentionally drifts out of the lane. The system can alert the driver and even provide countersteering force to the wheel to keep the vehicle from deviating. This technology has been deployed in private vehicles, but is still an emerging technology for transit vehicles.

Benefits to Transit

Lane assist technology has the potential to deploy more bus rapid transit (BRT) systems. Because of the limited right-of-way available to build new lanes for BRT operations, lane assist technology can allow the vehicles to be operated in lanes barely wider than the vehicles themselves, such as in freeway shoulders. In addition to allowing for narrower lane construction, the technology can help buses pull up to stops with an accuracy within centimeters, allowing for faster loading and unloading of passengers, especially those with special needs.

Lane Assist Technologies

The technology can take many forms, each with different advantages and disadvantages in cost, ease of implementation, and reliability.

Optical Guidance

Optical guidance device

Vision-based systems use machine vision equipment (cameras, image processing equipment, pattern recognition algorithms, etc.) to track a painted line in the road, which allows the on-board system to determine the vehicle's position. The system then steers the vehicle, following the trajectory of the painted line. Optically guided bus systems do not require significant infrastructure outlays, but maintenance costs can be high and it is very sensitive to weather conditions that might affect visibility.

The TEOR bus system in Rouen, France is the most well-known example of an optically guided BRT system, even though they use it primarily for precision docking. Cameras track a dashed line on the road, while drivers only control the vehicle's speed. Rouen has not applied the technology to automatic steering between stations, instead using it for only short stretches. Drivers have reported satisfaction with the technology, since it reduces stress and allows them to interact with passengers more.

Mechanical Guidance

Curb guided bus

Curb guided buses, also referred to as kerb guided buses, have small guide-wheels attached to the front steering mechanism of the bus. The wheels engage with the vertical side of a guideway curb, which is specifically constructed to guide the vehicle along its route. Away from the curb, the operator controls the vehicle as normal. Curb guidance has been successfully used in many cities and has many advantages. It is extremely reliable to operate, and the mechanical components are easy and straightforward to maintain. However, the infrastructure costs are high, and in many cities there is not enough right-of-way to create a dedicated lane.

Rail guided buses have a large rubber wheel that is guided by a rail embedded within the pavement. It provides an experience closer to that of a light rail or trolley, and has high infrastructure costs.

GPS Guidance

Minnesota's MetroTransit uses a combination of GPS and other technologies to operate express buses in freeway shoulders. There are many advantages to operating buses on shoulders, such as low infrastructure costs, increased reliability, and faster operations. However, shoulder use is at the driver's discretion and depends on traffic speeds and weather conditions. Lane assist technology has greatly helped drivers safely operate 9.5 ft. wide buses on 10 ft. wide lanes.

The system uses GPS satellite positioning technology and an on-board map database of the bus route to continuously identify the location of the bus on the roadway with centimeter-level accuracy . A head-up display (HUD) mounted between the driver’s face and the windshield shows the location of lane boundaries, helping drivers remain safely on the shoulder even when roads are snow-covered or visibility is low. Information about other vehicles or objects on the roadway, detected by laser sensors mounted on the front and sides of the bus, is also displayed on the HUD to help drivers avoid potential collisions. The HUD displays warnings if the bus starts to drift, and provides countersteering force to keep the vehicle within the lane.

Magnetic Guidance

Magnetic material, such as tape or plugs, are placed in the center of the bus lane, and magnetometers in the vehicle sense the strength of the magnetic field. Onboard software calculates the location of the vehicle, and then steers it according to the magnetic field. The technology operates well under different weather conditions and can correctly calculate the vehicle's position within centimeters. However, all experiments with magnetically guided buses have been very costly. Additionally, installation of magnetic plugs requires the pavement to be broken, which can cause future pavement problems in cold climates.

For many years, California PATH has been testing magnetic guidance systems, and they recently have improved the technology's potential for bus steering and precision docking In test tracks, PATH has shown the technology's ability to not only steer but also control the speed of the vehicle, creating a true "auto-pilot" system for the bus. Researchers suggest magnetic guidance is a relatively inexpensive addition to a BRT project which would create a light rail-like system at a fraction of the cost of true light rail .

Additional Reading

Tan, H.S. et al. (2009). "Field Demonstration and Tests of Lane Assist/Guidance and Precision Docking Technology." California PATH Program at University of California, Berkeley.

This California PATH document reports the improvement and implementation of the magnetic lane guidance and precision docking system on a 60ft articulated bus and the extensive testing in a real-world operation setting. The field studies provided valuable lessons that for the future deployment of the technology on a large, public scale.

Donath, M. et al. (2003). "Bus Rapid Transit Lane Assist Technology Systems. Volume 1: Technology Assessment." Federal Transit Administration.

This report asses various lane assist technologies available for BRT.

Alexander, L. (2005). "Bus Rapid Transit Technologies: Assisting Drivers Operating Buses on Road Shoulders Volume 1." Intelligent Transportation System Institute.

This technical report looks at existing lane assist technologies for buses, and suggests improvements to GPS driver assist systems.