Collision Avoidance >Lane Departure Warning Systems

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• Introduction
• Operations and Benefits
• Costs
• Companies
• Websites/references

INTRODUCTION

Lane Departure Warning Systems

In-vehicle lane departure warning systems could reduce road-departure crashes by 10% each year. Road Departure Collision Avoidance Systems could prevent about 458,000 of the 1.2 million single-vehicle run-off-road crashes each year.

Lane Drift Warning Systems (LDWS) are designed to reduce road departure crashes through in-vehicle driver notification or warning. Available technology uses an in-vehicle camera-based system to monitor vehicle position within its travel lane, and warn the driver if the vehicle drifts out of a lane unintentionally as a result of driver drowsiness, distraction, or inattention. The system may activate in-vehicle countermeasures such as directional audible or haptic (vibration) signal systems to inform the driver which way to steer. reference

These systems track the lane or road edge and suggest safe speeds for the road ahead. Future capabilities may integrate an adaptive cruise control function to adjust vehicle speed for the shape of the road, based on input from a map database and navigation system. Eventually, in-vehicle sensors will assess road surface conditions (wet, icy, etc.).

To reduce crashes caused by unintentional lane departures, lane departure warning systems (LDWS) monitor the position of a vehicle within a roadway lane and warn a driver if the vehicle deviates or is about to deviate outside the lane.

Currently available LDWS are forward-looking, vision-based systems that use algorithms to interpret video images to estimate vehicle state (lateral position, lateral velocity, heading, etc.) and roadway alignment (lane width, road curvature, etc.). These LDWS use a forward-facing camera that is mounted to the windshield in the cab of the vehicle. The systems also include an electronic control unit and a warning indicator. Some LDWS may issue directional warnings to alert the driver to which side of the lane the vehicle is drifting. A directional warning may be audible, such as rumble strip sounds in left or right in-cab speakers, or tactile. LDWS may graphically indicate on a user interface display how well the vehicle is centered in the lane on a time-averaged basis.

LDWS warn the driver of a lane departure when the vehicle is traveling above a certain speed threshold and the vehicle's turn signal is not in use. In addition, LDWS notify the driver when lane markings are inadequate for detection, or if the system malfunctions. LDWS do not take any automatic action to avoid a lane departure or to control the vehicle; therefore, drivers remain responsible for the safe operation of their vehicles.

Although traditional LDWS do not take any automatic action to avoid a lane departure or to control the vehicle, some emerging systems actually incorporate the use of a steering shaft actuator. If the driver does not react appropriately to a lane departure warning, the system automatically applies torque to the steering wheel and steers the vehicle back within the lane boundaries.

Application

LDWS can help prevent single vehicle roadway departure, lane change/merge, and rollover crashes involving large vehicles.

To help avoid single vehicle roadway departures, LDWS issue a warning as the vehicle crosses the shoulder lane marking. Without the system, the vehicle might be driven off the shoulder and crash into off-road obstacles (e.g., light poles, signs, guardrails, trees, and stopped vehicles) or roll over.

In unintentional lane change/merge situations, LDWS issue a warning as the vehicle crosses center lane markings on multi-lane roadways, including solid lines, double lines, dotted lines, dashed lines, and raised pavement markers (Bott's Dots). Without the system, the vehicle might be driven into an adjacent lane, resulting in a head-on or sideswipe collision.

LDWS may also help prevent rollover crashes. For example, if the vehicle drifts out of the lane onto the shoulder, the vehicle could roll over if a sudden recovery maneuver is made. In addition, a vehicle may roll over due to any recovery maneuver involving a high lateral velocity (rate of departure), requiring a relative large amplitude and/or rapid steering action.

Other potential benefits from the use of LDWS include:

    * Assisting the driver in consistently keeping a vehicle in the lane, thereby reducing lane-departure crashes.
    * Encouraging the driver to use turn signals when changing lanes (otherwise, a lane departure warning sounds).
    * Reinforcing driver awareness of vehicle position in the lane to maintain a more central lane position and improve the driver's attentiveness to the driving task.

Implementation examples/Companies:
Nissan's luxury division, Infiniti, is offering a system, developed by Iteris and supplied by Valeo, on its 2005 FX45 sport utility vehicle, Infiniti's second application of the Valeo LaneVue system will be on its 2006 M performance sedan, which goes on sale next spring.

In Europe, Valeo is also supplying the system to the 2005 C4 and C5 sedans from Citroen, recently introduced at the Paris auto show.

Implementation Example

A $20.5 million project under study by Visteon Corp., the University of Michigan Transportation Research Institute (UMTRI), Assistware Technology and the U.S. Department of Transport (USDOT). While existing lane departure systems rely on optical and sensors to determine a vehicle's position relative to road markings, the Visteon/UMTRI project integrates radar and GPS technology to provide a more comprehensive driver assistance system. Dubbed "road departure crash warning" (RDCW) technology, the system under development warns drivers drifting out of their lane and helps drivers adjust speed for negotiating curves.

Currently, the Visteon/UMTRI system is undergoing a field test that involves a fleet of 11 Nissan Altimas and a group of 78 volunteer drivers recruited at random in the lower Michigan area. According to James Sayer, a UMTRI human factors scientist involved in the program, the Altima was chosen because the vehicle has an electrical BUS system that made it possible to link the various pieces of on-board experimental equipment. The basic purpose of the test, which lasts through next February, is to assess the safety benefits, driver acceptance, system performance and capability and the market potential and pricing range.

The RDCW system provides two distinct modes of driver warning that are designed to minimize nuisance and gain credibility with the driver for the time when a mad departure warning is truly needed. The first type of warning is to prevent the drift-off-road problem that arises from inattention or drowsiness. A second type of warning is to alert a person who is driving too fast for an upcoming curve. Both functions provide warning, only, and do not intervene in vehicle control.

UMTRI's 'lateral drift warning" (LDW) function operates in similar fashion to other lane departure warning systems in that it relies on a forward-looking video camera in order to measure vehicle position and lateral velocity relative to lane and mad-edge markings. However, the system adds another layer of sophistication through the use of four radar units mounted in the front fascia. These forward and side facing radar units assess the room available on the shoulder for performing a recovery maneuver. When ample room is present, warnings are delayed to avoid nuisance alarms that often result from early warnings. However, when little room is available, the warnings are given early so that the driver has enough time to respond and avoid a crash.

When drift-off is detected, the LDW system provides audio, visual, and seat vibration warnings. Drivers receive either a cautionary or imminent alert, based on lane position, lateral movement, and the type of lane boundary. A cautionary alert occurs when the driver is crossing a dashed-line boundary with no vehicles in the drift path. The alert appears as a yellow icon on the dashboard display and as a vibration on the left or right side of the driver's seat, depending on the direction of lateral drift. An imminent alert occurs when the driver approaches or has crossed a solid-line boundary or when crossing a dashed-line boundary while a vehicle is present in the drift path. A red icon appears on the display and a buzz sounds on the side of the vehicle at which the threat is developing.

LDW becomes inactive in the following conditions: on unpaved roads, roads with poor lane markings or badly defined road edges, and at speeds below 25 mph. LDW automatically turns off when drivers engage the turn signal so that they can change lanes without receiving a warning. Among the issues being analyzed by Sayer and the UMTRI team is the question of driver distraction. "People ignore warnings, it's the cry wolf phenomenon," says Sayer. "We have to be careful not to give false warnings or else people will switch the system off. Another consideration is what is the best type of auditory warning system. Also, we have to consider whether people will rely on the system and take on extra tasks."

A separate element to the Visteon/UMTRI system is known as curve speed warning (CSW). This function alerts drivers if they are traveling too fast to successfully negotiate an upcoming curve. The CSW function uses GPS data and a precise, on-board map database to determine the current vehicle position, the most likely future path, and the geometry of the road along that path. A CSW alert would be issued when, based on the current vehicle position and speed, a substantial level of braking is needed to achieve a safely controllable speed in the curve ahead.

Drivers receive either a cautionary or imminent alert, based on the degree of overspeed and their remaining distance to the curve. A cautionary alert indicates that a modest degree of braking is needed to avoid overspeed on the curve. The alert appears as a yellow icon on the display and as a vibration at the front of the driver's seat. An imminent alert indicates that a relatively high level of braking is required to avoid a run-off-road collision. A large red icon appears on the visual display and a voice warning says "Curve! Curve!"

CSW becomes active at speeds above 18 mph as long as GPS satellite tracking and map database coverage are available. For the purposes of the UMTRI test program in southeastern Michigan, the existing map database is fairly comprehensive, although Sayer notes that for widespread use, enhanced maps with exact curve radii w511 be needed in future. The system uses the mm signal and other cues to determine whether an upcoming exit ramp, or any other roadway branch, is likely to be the selected path.

On the UMTRI test vehicles, more than 300 channels of data are collected every tenth of a second, including vehicle speed, lane position, location of lane and road edges and objects around the vehicle, plus many signals indicating the driver's actions and the state of the vehicle. Data are gathered from radar sensors pointing toward the front and sides of the vehicle, video cameras pointed through the windshield and at the driver's face, and by means of several other instruments that monitor the motion of the vehicle and whether a cell phone is in use. The data acquisition system automatically sends a data sample from the vehicle to the UMTRI facility, via a cell modem, each time the ignition is turned off. A comment button, installed in the dashboard, allows drivers to record comments and suggestions any time they drive. One intended benefit of the lane departure systems being developed by Visteon, Valeo and Delphi is that they will encourage drivers to use their indicators. Failure to use turn signals is an increasing problem, especially among the U.S. driver population. According to Valeo, in some countries as many as one in 10 drivers do not use the indicator system before changing lanes.

Companies, organizations, test cases

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