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UNIT-I & II-ACCIDENT AVOIDANCE TRAINING. TABLE OF CONTENTS 4 INTRODUCTION 4 ARMY Regulation 4 Traffic Safety 4 Vehicle Safety 4 Defensive Driving 4 Night.

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Presentation on theme: "UNIT-I & II-ACCIDENT AVOIDANCE TRAINING. TABLE OF CONTENTS 4 INTRODUCTION 4 ARMY Regulation 4 Traffic Safety 4 Vehicle Safety 4 Defensive Driving 4 Night."— Presentation transcript:


2 TABLE OF CONTENTS 4 INTRODUCTION 4 ARMY Regulation 4 Traffic Safety 4 Vehicle Safety 4 Defensive Driving 4 Night Driving Tactics 4 Winter Driving Tactics 4 Safe Driving 4 Driving Safety 4 Heads Up at the Wheel: Home Safe 4 Hands on Driving Information 4 SAFETY ALERTS & Awareness Material 4 FT LEE FORM 1082

3 INTRODUCTION è Driving can lead to a false sense of security. You take most risks for granted. Driving becomes second nature. è Motor vehicle accidents are the single largest cause of accidental death. è Leading cause of on-the-job fatalities.

4 Introduction 4 Driving may be one of the most dangerous activities you engage in on the job. 4 By following the Ft. Lee Accident Avoidance Training handbook, you may be surprised to find that some of your driving habits are not as harmless as you thought. After all, even a good driver can improve.

5 ARMY REGULATION 4 AR : Prevention of Motor Vehicle Accidents requirement every 4 years 4 AR : The Army Driver and Operator Standardization Program (Selection, Training, Testing and Licensing)


7 TRAFFIC SAFETY Why is it important to keep your eyes and attention on the driving task?

8 4 Taking your eyes and attention off the driving task will mentally leave you blind to the driving environment. 4 At highway speeds, a one second distraction can permit you to travel blind for over 100 feet. Avoid inside and outside distractions to the driving task. Distractions are a leading contributor to vehicle accidents.

9 What is the purpose of delaying your start at a traffic light that has just turned green? 4 The first three seconds after a light turns green are the most dangerous. Drivers facing the newly turned red light may still be trying to make the light. Remember, having a green light does not give you the right to start moving immediately.

10 Traffic Safety Discussion 4 What is the purpose of scanning seconds ahead of your vehicle’s intended path? 4 What is meant by the concept road management ?

11 QUIZ 5 minutes

12 QUIZ 1. How far ahead should you scan your intended driving path? A. 0-2 secondsD seconds B. 2-4 secondsE seconds C seconds 2. What is the recommended safety cushion for vehicles you are following? A. 3 secondsD. 6 seconds B. 4 secondsE. 7 seconds C. 5 seconds C seconds A. 3 seconds

13 3. When stopping behind another vehicle, what should you be able to see? A. Tail lights of vehicle ahead D. Rear tires of vehicle ahead B. Bumper of vehicle ahead touching the ground C. Rear tires of vehicle ahead E. 15 feet of ground behind the vehicle ahead 4. The recommended delayed starting time at a light is? A. Delay not recommended D. 5 seconds B. 1 second E. 7 seconds C. 3 seconds 5. Proper seatbelt use reduces the likelihood of fatal or serious injuries by: A. Does not reduce likelihood C. 24% E. 44% B. 14% D. 34% D. Rear tires of vehicle ahead touching ground C. 3 seconds E. 44%


15 4 Each vehicle and type of vehicle has its own handling characteristics. Drivers should be trained on the vehicle they operate. Follow the same driving rules on and off-site. Do all vehicles handle and operate the same?

16 4 To illuminate the path of the vehicle. 4 To help others locate the vehicle and determine its activity (braking, turning, backing, etc.). What purpose do the lights on a vehicle serve?

17 4 To avoid collisions with other objects in the vehicle’s path. 4 To hold the vehicle in place while parked. 4 To slow the vehicle so it can stop or make appropriate turns. What is the role of the braking system of a vehicle?

18 QUIZ 5 minutes

19 QUIZ 1. Which statement(s) about vehicles on a facility is true? A. Each vehicle has its C. Drivers should be trained own operating procedures on vehicles they operate B. Drivers must know & follow D. All of the above each vehicle’s operating E. None of the above procedures 2. A vehicle’s lighting system exists for which of the following purposes? A. To help the driver see his/her path of travel B. To warn others of the vehicle’s presence C. To inform others of the vehicle’s activity D. All of the above E. None of the above D. All of the above

20 3. Based on the concept of one vehicle length per every 10 mph of travel, how many vehicle lengths should you be behind a vehicle traveling 30 mph? A. One C. Three E. Five B. Two D. Four 4. What types of problems can the noise from some industrial vehicles create? A. Driver’s inability to hear C. Driver’s inability to steer the warning devices vehicle B. Driver’s inability to see D. All of the above approaching vehicles or E. None of the above pedestrians A. Driver’s inability to hear warning devices C. Three

21 SAFE DRIVING View Videos: 5 Rules of Defensive Driving Heads Up At the Wheel

22 Why should you check outside the vehicle before putting the vehicle in motion? 4 To ensure no objects will interfere with the movement of the vehicle. 4 To ensure tires are in good condition. 4 To ensure the windows are clean. 4 To identify any unexpected body damage to the vehicle.

23 4 A driver not getting proper rest; and not being alert. If your vehicle is well maintained, what else can affect motor vehicle safety? What types of emergency equipment should be with the vehicle? 4 Warning flares or triangles, jumper cables, fire extinguisher, first aid kit, & equipment to change a flat.

24 What is meant by properly securing the driver and goods? 4 Driver properly belted in 4 Passengers wearing seatbelts 4 Cargo properly secured so it can’t move around during travel.

25 How do senses other than vision help in driving? 4 Provide warning that something is not right. smells alert you to something burning unusual engine sounds may indicate a mechanical problem your body may alert you to bad brakes or improper tire inflation by feeling the vehicle pull to the left or right when braking

26 Good visual driving habits: 4 Keep eyes moving (check out your path of travel) 4 Look 15 seconds ahead of your vehicle. (it provides a picture of what’s happening) 4 Scan mirrors every 4-6 sec. (find out what’s happening behind and along side your vehicle) 4 Glance at dashboard every 20 sec. (observe speed control and warning gauges) 4 Follow vehicles ahead no closer than 3 sec. (allows for reaction time if needed)

27 QUIZ 5 minutes

28 QUIZ 1. Outside the vehicle, you should check for: A. Objects that could interfere C. Bad tire pressure or loss in the movement of the vehicle of fluids B. Vehicle damage not D. All of the above previously reported E. None of the above 2. Taking care of the vehicle and yourself means? A. The driver getting plenty of rest B. The vehicle receiving proper maintenance C. Having emergency supplies in the vehicle D. All of the above E. None of the above D. All of the above

29 3. Good visual search patterns while driving: A. Provide the driver with needed information to safely drive from point A to point B. B. Include looking inside of the vehicle and under the hood as much as looking outside of the vehicle. C. Include maintaining a minimum 10 sec following distance. D. All of the above E. None of the above 4. Seatbelts should be worn: A. Only when traveling short distances B. Only when traveling long distances C. Any time the vehicle is in motion D. Only when confronted with dangerous driving conditions E. When your supervisor is present C. Any time the vehicle is in motion A. Provides driver with needed info to safely drive from point A to point B.QUIZ

30 QUIZ 5. When driving in bad weather, the driver should: A. Allow more time to secure the cargo B. Allow more time to stop the vehicle C. Take fewer rest stops to get home faster D. A and C E. A and B E. A and B


32 Four strategies that make for a safe driver: 4 Driver has behaviors and attitudes appropriate to the driving task. 4 Driver follows appropriate driving behaviors. 4 Drivers see to it that their vehicle is properly maintained and loaded/unloaded. 4 Drivers comply with organizational policies as they relate to safe operation of a vehicle on and off the facility.

33 Driving Safety Discussion What is meant by the need to develop a high emotional tolerance level to other drivers?

34 QUIZ 5 minutes

35 QUIZ 1. Which of the following behaviors is common to a driver with an inappropriate driving attitude? A. Speeding D. Accelerating towards a B. Tailgating caution light C. Needless risk taking E. All of the above 2. The minimum distance you should maintain when following another vehicle is: A. 4 seconds D. 7 seconds B. 5 seconds E. None of the above C. 6 seconds E. All of the above E. None of the above

36 3. Which of the following items should be included in a pre-drive checklist? A. Tires D. All of the above B. Wipers E. None of the above C. Brakes 4. Alcohol consumption followed by driving has which of the following impacts on the driver? A. Improved vision B. Improved hearing C. Reduced concentration D. Reduced distractions E. All of the above C. Reduced concentration D. All of the aboveQUIZ

37 QUIZ 5. Your organization’s policy on vehicle operation is intended to protect: A. You the operator B. Your supervisor C. The organization D. The product (equipment) E. All of the above



40 HANDS ON DRIVER’S TRAINING 4 TIME: 1 hour 4 1 Qualified Instructor - must be with the student(s) 4 Ensure travel map/driving instructions are discussed prior - choose variety of roadways 4 Critique student

41 TRAINING COMPLETION 4 Fill out the Ft Lee Accident Avoidance Training card (FT LEE FORM 1082) 4 Instructor’s signature & date



44 INTRODUCTION 4 Automobile Industry is undergoing a BIG TRANSFORMATION never seen before. 4 Today CAR’s are not only used for personal Transport but they are ENCOMPASSED with Entertainment that vies with the fedility of your HOME THEATRE Seating arrangement more comfortable than your RECLINER SAFETY FEATURES making your car safer than a TANK

45 Globally car companies Spend nearly $36 billon annually for influencing new TECHNOLOGIES into their cars.Globally car companies Spend nearly $36 billon annually for influencing new TECHNOLOGIES into their cars. Some of the big advancement in Automotive Industry in last 10years have come in a area of SAFETY.

46 In addition to Telematics based Services like Digital Satellite Radio In car GPS systems Recent Advancement in Braking Technology have led to Shorter stopping distance Increased Control in PANIC situation More control on CURVED turns

47 Air Bags What’s the main function of the System? Material of Airbags? History

48 Actual Working Airbag Before CollisionAirbag After Collision

49 Inflation unit How does it INFLATES?

50 Effectiveness This system has proven its effectiveness In frontal crashes reduction in d rivers death reduced by nearly 14% Passenger side airbags reducing death by nearly 11% NHTSA estimated reduction in risk by nearly 85% with the combination of seat belt and airbags compared than only seatbelt i.e60% Car Model Head Injury Risk Airbag Airbag No Airbag No Airbag Holden Commodore Holden Commodore 2848 Toyota Camry 2044 Mitsubishi Magna 627 Ford Falcon 14 N. A. This are some crash results which give the effectiveness of the system

51 Different types of Airbags DRIVERS SIDE AIRBAG

52 PASSENGER AIR BAG Curtain Airbags

53 Anti-lock Braking System Introduction? Advancement in the system? Working?

54 Advancement in the system?

55 How Does the system Works?

56 Working 4 Conventional Braking  Whole process is controlled by driver applied break paddle pressure ; 4 ABS Braking  Electric Sensors monitor the wheel speed  ABS microprocessor Compares the wheel speed  Control valve is energized.

57 Effectiveness ABS on a test track

58 Advantages:  Achives the Shortest Stopping distance  Better chance on Steering around obstacle  Reduced risk of skidding Disadvantages :  Precautions should be taken while driving  Proved less effective on gravel road or road compacted by snow

59 Traction Control 4 Next Generation ABS 4 Uses ABS as a Building block. 4 Can be is a combination of ABS & Engine control

60 Mainly the system has to control some or all conditions  Retard or Suppress the spark to one or more cylinders  Retard fuel supply to one or main cylinder  Break one or more wheel  Close the throttle, if the vehicle is fitted by wire throttle

61 Electronic Stability Control

62 Main components of the system A) active wheel speed sensors; B) steering angle sensor; C) Yaw rate sensor D) attached electronic control unit (ECU) E) motor; F) pressure sensor, G) hydraulic unit.

63 Steering Angle Sensor Understeering (“plowing out”) Oversteering (“spinning out”)

64 Some important ECS definitions ESC augments vehicle directional stability by applying and adjusting the vehicle brakes individually to induce correcting yaw torques to the vehicle. ESC is a computer-controlled system, which uses a close-loop algorithm to limit under steer and over steer of the vehicle when appropriate

65 Case Study A S-Class Mercedes sedan testing Bosch's ESP system



68 1. The Problem 4 Vehicles and highways have greatly improved safety: total fatalities are down approximately 30% over the past 35 years 4 Even with those improvements, there are still approximately 40,000 fatalities / year in the US 4 People haven’t improved: in 90% of all accidents, the driver is a contributing cause

69 The Solution 4 The Intelligent Vehicle Initiative (IVI) is a USDOT program to use advanced electronics to improve vehicles, with the dominant concern being safety. 4 This tutorial is arranged around a series of advanced functions, such as vehicle detection, that contribute to safer and more intelligent vehicles. For each function, the tutorial discusses a set of possible technologies. 4 The next set of slides show the “user services” for the IVI advanced vehicle control and safety systems. The following charts show which technology functions support each user service. 4 Note the synergy: each technical function supports many user services.

70 IVI User Services categories: 4 Safety: (directly contributing to vehicle safety); rear end collision warning roadway departure warning lane change / merge collision warning intersection collision warning railroad crossing collision warning vision enhancement location-specific warnings collision notification 4 Safety Impacting: (potential to distract or aid the driver); navigation and routing real-time traffic information driver comfort and convenience features

71 More Services 4 Commercial Vehicle Services: vehicle stability vehicle diagnostics driver condition monitoring cargo identification automated transactions safety recorder 4 Transit: obstacle and pedestrian detection precision docking passenger monitoring passenger information

72 More Services 4 Specialty Vehicles: full automation 4 Supporting Services: low friction warning longitudinal control lateral control

73 Technical functions 4 There is a set of common vehicle functions that underlie those user services: sensing the position of other vehicles sensing obstacles sensing the position of the lane relative to your own vehicle sensing vehicle position and motion estimating braking performance communication reliability miscellaneous functions sensor-friendly vehicles and roadways 4 The rest of this section shows how each of these functions supports the various user services

74 Safety 1

75 Safety 2

76 Safety Impacting

77 Commercial Vehicle

78 Transit

79 Specialty

80 Supporting

81 Section 1 Questions: 4 How many accidents occurred in the most recent year for which statistics are available? Hint - l and l 4 How many fatalities? 4 What was the dollar cost of those accidents? 4 What kind of economic justification is there for the various AVCSS services? 4 Are there other on-vehicle functions that would be useful?

82 2Sensing Other Vehicles 4 Other vehicles need to be sensed in front for adaptive cruise control and forward collision warning; on the sides, for blind spot and lane change / merge warning; and behind, for backup warning and for lane change / merge warning of overtaking vehicles. 4 Sensing has to work in all weather, and at a variety of ranges

83 2.1Basic Geometry Sensing straight ahead is not sufficient; on a curving road, a forward-looking sensor needs to have a wide field of view, and sensed vehicle position needs to be combined with road geometry to know whether the lead vehicle is in your lane, another lane, or on the shoulder.

84 2.2Targets and Clutter 4 Other objects in the field of view can include roadside signs, parked cars, overpasses, guard rails, etc; this is referred to in the radar literature as “clutter”. 4 Adaptive Cruise Control (ACC) systems, which are only concerned with moving vehicles, can reject any stopped object as clutter. 4 Rear-end collision warning systems need to sense stopped vehicles, and so need high-acuity sensing of vehicles and lanes in order to separate targets (other vehicles) from clutter.

85 2.3Radar 4 Radar is an excellent choice for seeing big metal objects through fog, snow, or light rain 4 The currently approved frequency is 77 GHz. Radar works at the speed of light, so sensing is almost instantaneous. 4 Simple radar is be a single spot with no information on bearing angle. More sophisticated versions sweep the beam mechanically, or use two or more beams and various processing schemes to measure bearing and range 4 Typical resolution (closest objects that can be distinguised) is 1 meter in range, 3 degrees in bearing.

86 Radar Data Data from a scanning radar. Top image is video of the scene, bottom is radar data, with corresponding locations marked. The radar data is range (horizontal) and bearing angle (vertical; up is left, down is right). Brightness indicates strength of return. Car A is close and he center of the radar return (the video image does not extend as far to the right as the radar); B is further and left; C is further yet and is barely visible above the roof of A; D is much further and has a bearing between A and B.

87 2.4Ladar 4 Ladar, lidar, and laser rangefinder are all synonyms. They refer to measuring distance using the travel time of a laser beam. The laser can be scanned over the scene with mirrors to produce a “range image”. 4 Lasers can be focused to very small spots (fractions of a degree), so they have much better resolution than radar. Instead of sensing a blob with radar, a ladar can make many measurements as it scans, and can measure fine details of shape. 4 Since ladar is near visible light, it is blocked by the same kinds of effects that impede human vision: fog, snow, and heavy rain will block the signals.

88 Ladar Data 4 The figures on the next page show data from a high- resolution scanning laser rangefinder. Each picture is 480,000 pixels (points), each corresponding to a separate ladar measurement. 4 The top picture shows the reflectance data: this is the amount of laser energy returned from that point in the scene, and is roughly equivalent to a flash photo. 4 The lower picture shows range data. Brightness encodes range: points that are further away are displayed more brightly. 4 Note the fine details of shape and appearance visible in this data. It is possible to build a computer program that can identify which objects are cars, and which direction they are facing; this can give early warning of which vehicles may be on a collision course.

89 Ladar Data

90 2.5Sonar 4 Sonar works by measuring the time of flight of sound. 4 Sound travels (relatively) slowly though air and is hard to focus, so sonar is only useful for detecting objects at ranges of a few meters or less. 4 Sonars are inexpensive, and work in a most weather conditions. The initial mass market application was in Polaroid auto-focus cameras. 4 Sonars are commercially available for blind spot sensors and back-up warning sensors.

91 Side and Rear Sensors Radar Sonars This bus is equipped with rear and side sensors for blind spot coverage

92 2.6Communications 4 If all vehicles on a roadway are equipped with ITS features, inter-vehicle communications can be used to determine relative positions. 4 Each vehicle can broadcast its current location, derived from GPS or other positioning systems. 4 Vehicles can also broadcast other information, such as speeds, intent to change lanes, or onset of emergency braking. This is crucial in decreasing inter-vehicle spacing to increase throughput, while maintaining safety. 4 This kind of scheme is most appropriate for high-end IVI systems, such as automated highways. 4 The picture on the next page shows a “platoon” of tightly-spaced automated vehicles, developed by the PATH program at UC Berkeley. Platoons rely on communications 20 times a second to keep all vehicles moving smoothly together.

93 Platoon

94 2.7Driver models 4 Sensing the current location of a nearby vehicle is not all: it would be even better to predict future actions of the vehicle. Unless that vehicle is fully automated, it is necessary to model the behavior of that driver. 4 As shown in the next slide (and as everyone knows from personal experience), there is a great deal of variability in people’s driving behavior. 4 If a particular vehicle can be observed for some time, that driver’s behavior can be estimated, and used to predict future actions.

95 Driver Differences The five drivers plotted here each have different behaviors for one important component of driving: average lane position. They have different mean lane positions when the road is straight, and cut the corners by different amounts when the road curves Left curve StraightRight curve

96 Section 2 Questions: 4 What are the advantages and disadvantages of using radar vs. ladar? 4 The speed of light is about 3*10^8 m/sec, or, for a rule of thumb, a foot / nanosecond. How long does it take a radar pulse to go to and from an object 150 m away? 4 Find two manufacturers of automotive or truck radars on the www

97 3Sensing Obstacles 4 Obstacle detection is much more difficult than vehicle detection: obstacles can be small, non-metallic, and much harder to see 4 Obstacles can be stationary or moving (e.g. deer running across the road) 4 For a passenger car at highway speeds, obstacles need to be detected 100 m ahead. For trucks, the distance is even longer. 4 Obstacle detection is one of the most challenging tasks for an intelligent vehicle

98 3.1Obstacles on the Road  State DOTs report cleaning up construction debris, fuel spills, car parts, tire carcasses, and so forth.  State highway patrols receive reports of washing machines, other home appliances, ladders, pallets, deer, etc.  A survey commissioned by a company that builds litter- retrieval machines reports 185 million pieces of litter / week.  Rural states report up to 35% of all rural crashes involve animals, mostly deer but also including moose and elk as well as farm animals.  A non-scientific survey of colleagues indicates that people have hit tire carcasses, mufflers, deer, dogs, even a toilet.

99 3.2Sensors 4 Ladar, in its high-resolution scanning formats, is useful for seeing small objects 4 A variant is to use the reflectance channel of a ladar, and to look for bright returns, which probably come from objects sticking up out of the roadway. 4 Sonar has insufficient range 4 Advanced radar and stereo vision systems may work

100 3.3Polarimetric radar 4 Radar can be polarized in the same was as light. 4 Just as polarized sunglasses help reduce light reflected from shallow angles (glare), polarized radar transmitters and receivers can separate the return from different polarization directions; this provides cues to distinguish horizontal surfaces and from vertical surfaces. 4 Polarimetric radars built at U of Michigan are much better than ordinary radar at separating small obstacles from ground clutter. 4 There is also some evidence that polarimetric radar will give different returns for wet or snowy roads, giving some information on road conditions.

101 3.4Stereo vision 4 Stereo works by finding the same point in two or more cameras. Intersecting the lines of view from the cameras gives the 3D location of the object.

102 Stereo Guided Segmentation 4 Low-resolution stereo for detection and recognition of nearby objects, used for side-looking sensors on a bus. 4 Left: Original image. Center: depth map from stereo; brighter is close. Right: “blobs” of pixels at the same distance. The overlays on the original image show detected objects, two pedestrians and a car. 4 Further processing can examine each blob to separate people from fixed obstructions, and generate appropriate driver warnings

103 Long-Range Stereo Top: One of three images from a stereo set. The objects on the road are 15 cm tall at a range of 100 m from the camera. Bottom: detected objects in black. Besides the obstacles on the road, the system has found the person, the sign, grass along the road, and a distant dip in the road

104 Section 3 Questions: 4 Look up the connection between posted speeds and vertical curvature in the AASHTO handbook. Is the line of sight for a human driver, going over the crest of a hill, better or worse than for a sensor mounted in the front bumper? 4 For extra credit, go out and run over obstacles with your car, and decide what is the largest object you would be willing to hit, and therefore the smallest object that needs to be detected.

105 4Sensing Lane Position 4 Knowing lane position is necessary for automated guidance and for lane departure warning systems. It is also important for rear-end collision warning, to know which lane your vehicle is in as well as which lane preceeding vehicles are in. 4 Requirements are somewhat different for each application.

106 4.1 Requirements reliability: high for warning systems, extremely high for automated guidance availability: must be available nearly 100% for automated guidance; lower availability acceptable for warning systems provided a warning is given weather: should operate in most weather, warn and disable if not operating accuracy: absolute accuracy of better than 30 cm needed; no high-frequency jitter allowed for control applications range: rear-end warning requires knowing lane position of leading vehicle, to approx. 100m

107 4.2Magnetics UC Berkeley has pioneered the use of permanent magnets, buried in the center of the road, for lateral guidance. The magnets can be inexpensive magnets, as shown here, for most applications; or more expensive but much smaller magnets for bridge decks where drilling large holes would damage the structure. The magnets are sensed by magnetometers underneath the front and rear bumpers of the vehicle to provide lateral position information. The magnets can be installed north pole up or down, providing a simple binary code that can indicate e.g. map location.

108 More Magnets An obvious advantage of magnets is that they are not affected by weather. Here, they are used to mark the edge of the shoulder, to provide a visual indicator to the snow plow operator. Besides buried magnets, there are also efforts to place magnets in lane marking tape. This would be less expensive to install, but requires more sophisticated sensing, since the magnets are not directly underneath the vehicle’s sensors.

109 4.3Buried cables The oldest way to perform automated guidance, going back to the 1950’s, is to follow a buried cable. The automated trucks at the Westrack pavement test site use two cables for redundancy, with pickup coils mounted in triangular frames at both front and back of the truck. Buried cables are all-weather, and the signal on the cable can be used to send messages (e.g. “speed limit change”). But cable installation and maintenance are difficult.

110 4.4Radar reflective surfaces Collision avoidance radar can be used for lateral control with modified lane-marking tape. Frequency-dependent tape properties can provide distance and other information Conventional lane marking tape (3M Corp.) punched with specific hole pattern to provide frequency-selective retro- reflection

111 4.5Vision Typical vision system for lane tracking. The detected position of the solid line is shown by the blue dots; the detected dashed line by dark and light blue dots. Overlayed on the image is data from other sensors, showing the location of radar targets: yellow X for right lane, red X for current lane. Experimenter interface shown at bottom.

112 Section 4 Questions: 4 What would be the relative advantages of magnetics vs. vision? 4 What is the disadvantage of buried cables?

113 5Sensing vehicle position and motion 4 An estimate of vehicle motion, and position on a map, can be used in several ways, depending on the resolution. For example: coarse position (10s of meters) can be used to predict that a corner is coming up medium position (meters) can be used to warn a driver to slow down, based on the design speed of the upcoming curve fine positioning (cm) can be used to tell if the driver is drifting out of their lane through the curve 4 Several different technologies provide ways of measuring absolute position and motion, at a variety of resolutions.

114 5.2GPS 4 The Global Positioning System is a satellite- based navigation system, originally developed by the US military. It works by broadcasting very accurate time signals from a constellation of orbiting satellites. A ground-based receiver can compare the times from several satellites; the different in apparent times gives the difference in time-of-flight of the signals from the satellites, and therefore the difference in distance to each satellite. Simple geometry gives the location of the ground-based unit and an accurate time.

115 More GPS 4 This simple picture is distorted by two phenomena The US government deliberately introduces distortions into the civilian version of the signal, in order to reduce the accuracy of the system for potential enemies Local atmospheric effects refract the signals by varying amounts 4 The result is that raw GPS has an accuracy of only 10’s of meters

116 Differential GPS 4 In Differential GPS, a base station has a GPS receiver at a known location. It continually compares its known position with the GPS reported position. The difference is the error caused by selective availability and atmospheric distortion. The base station broadcasts the correction terms to mobile units. By applying the correction, the mobile units can reduce their errors. 4 The accuracy of DGPS is on the order of a few meters.

117 Carrier Phase GPS 4 In carrier phase systems, the base station and the mobile units watch both the broadcast time code, and the actual waveforms of the carriers. By counting waveforms, they can synchronize their positions with each other to a fraction of a wavelength. 4 A good carrier-phase system, with good conditions, can achieve accuracies of 2 cm or better.

118 GPS Difficulties 4 GPS requires a clear view of at least 4 satellites. For aircraft applications, or in flat, open terrain, this is not a problem. 4 In mountainous terrain, or in urban canyons, GPS signals can be blocked or (worse) can reflect from tall objects and cause mistaken readings. 4 Carrier-phase GPS is very sensitive to losing lock on the satellites, and can become confused even going under a large road sign.

119 Bottom line on GPS 4 GPS is very useful for many applications. 4 It is not yet 100% reliable, so is not ready for control applications. 4 Research continues on filling in gaps in GPS coverage, and integrating GPS with other sensors, so there is hope for the future.

120 Maps 4 Accurate position is not useful unless combined with accurate maps. 4 The first generation of digital maps were produced from paper maps, and therefore are no more accurate than the paper products. Typical quoted accuracies are 14 meters. This is sufficient for in-vehicle navigation systems; until more sophisticated uses arise, there is little market demand for high accuracy. 4 The next generations of maps will be produced directly from aerial photos and verified by driving selected routes with accurate GPS, so the accuracies will improve. 4 To be completely useful, maps should have additional information, such as design speed of curves, grade of slopes, etc. This would aid e.g. in warning drivers of excessive speed when entering a curve.

121 5.3Inertial 4 Inertial sensing measures acceleration, then integrates acceleration to give velocity and again to give position. 4 Since position is doubly-integrated, small errors in acceleration build up rapidly. 4 Inertial measurement is good for sensing braking forces or for comparing wheel speed with ground speed and calculating slip during braking. 4 High-precision inertial navigation is not yet affordable for the automotive market. 4 Inertial measurement is useful to fill in short- term gaps in GPS or other measurements.

122 5.4Other sensors 4 “Dead reckoning” uses estimates of distance travelled and direction of travel. 4 Odometry uses wheel encoders to measure distance traveled. It is susceptible to errors due to tire slip, incorrect estimates of wheel circumference due to changes in tire inflation, etc. Road Rally enthusiasts can calibrate their odometry to 0.1%; this is not practical for most vehicles. 4 Standard compasses are affected by nearby metallic objects, such as bridges or buildings.

123 More Sensors 4 Image correlators directly measure vehicle motion by watching the ground move by under the vehicle. These systems are accurate to better than 0.1% 4 Doppler radar is used in precision agriculture applications, where it is important to measure the speed of farm equipment even with significant tire slip.

124 Section 5 Questions: 4 Why can’t you just use a magnetic compass for heading? 4 What’s the cheapest GPS unit you can find on the web? 4 Why would Japan have a higher market penetration of GPS and moving map displays than the US?

125 6Predicting Braking Performance 4 Braking performance is key to setting many parameters in automated control and in driver warning systems. 4 To set safe following distance, ideally the system should know its own braking capability; the braking capability of the lead car; and the reaction time of the automated system or of the 4 Braking performance of vehicles on identical roadways can vary by a factor of 4

126 6.1Basic formulas 4 The basic formulas for the time and distance required to bring a car to a stop are Time = reaction time + speed / deceleration Distance = speed * reaction time + ½ speed 2 / deceleration 4 Typical highway speeds are approximately 30 meters / second; typical reaction times range from 100 milliseconds for a fast computer- controlled sensor and brake actuator, to up to 2 seconds for a human driver. The dominant unknown factor is deceleration, or braking performance.

127 6.2Wheel speeds and slip Force (g) Slip (%) Dry surface Wet surface Typical force vs. slip curve. As the brakes are applied, the tires begin to slip, which results in deceleration force. As the slip increases, the force increases to some maximum. After that point, the wheels begin to lock and skid, and the braking force decreases. Note that the curves for wet and dry pavement start off very close to each other, but reach different peaks. This means that gently tapping the brakes is not enough to tell surface type, and therefore it is difficult to predict maximum braking performance without attempting hard braking.

128 6.3Surface condition sensing 4 Several methods have been attempted to sense current surface conditions: infrared spectrophotometers, tuned to detect differences between ice, water, and dry pavement microphones in the wheel wells listening for water splash sounds roadside mini-weather stations with sensors built into the pavement careful instrumentation of all wheels of a car, looking for incipient slip on the driving wheels 4 None of the methods is completely successful yet.

129 Section 6 Questions: 4 Have you ever encountered “black ice” that you couldn’t tell was there? 4 Calculate stopping distance for the following parameters: Truck with 1.0 sec reaction time and 0.3 g braking Sedan with 1.0 sec reaction time and 0.7 g braking Sedan with sleepy driver, 1.5 sec reaction time and 0.7 g braking Sedan with poor brakes, 1.0 sec reaction and 0.5 g braking Sports car with professional driver, 0.5 sec and 1.0 g 4 Which factors dominate stopping distance?

130 7Reliability  Reliability engineering in intelligent vehicles is difficult. Several characteristics of automobiles are much different than, e.g., aircraft:  Cost sensitivity: Usual practices that involve triplex redundancy of critical components may not be affordable in automobiles.  Equipment used until end-of-life: In most safety- critical tasks, preventive maintenance schedules call for replacing electronics before the end of their design life. In the automotive environment, many components are never replaced until they fail.

131 More Reliability  Operation in uncontrolled environment: Vehicles operate in harsh environments, with relatively unskilled and untrained operators.  Very large scale of deployment: An extremely improbable event, one that occurs once in 10 9 hours, would cause one failure in 73 years in the US commercial air fleet. That same probability would cause a failure once every 4.5 days in the US automotive fleet, due to the much higher number of vehicles. Even though the risk to a passenger might be the same in both cases, the public perception of risk could be much higher for cars.

132 7.1Redundancy 4 Duplex redundancy refers to having two copies of a subsystem (e.g. computer). If a failure is detected in one system, the other can be used. 4 Triplex redundancy has three copies. for computers, the output of all three can be compared, and the majority wins; this provides automatic detection and correction of single errors. 4 Heterogeneous redundancy refers to doing the same function with different means. For instance, if a steering actuator fails on an automated vehicle, some steering authority is available by differentially applying the right or left brakes.

133 7.2System-level solutions 4 System level solutions build safety into the system by considering the entire system. In automated highways, the California PATH approach of Platoons is designed to mitigate the effects of an (unlikely) crash by having vehicles so closely spaced that any collision would be at a small relative velocity.

134 Questions: 4 How reliable is your car? Your computer? Would you trust your life to them? 4 Describe heterogeneous redundancy, and give an example.

135 8Emerging technologies 4 A number of other technologies are being developed that will support intelligent vehicles. 4 Some, such as electronic controls, are being developed for other purposes (e.g. handling), but will be useful for intelligent vehicles. 4 As drivers become more accustomed to electronics in vehicles, prices will fall, consumer acceptance will increase, and the pace of adoption of new technology could accelerate.

136 8.1Control 4 Current IVI applications are focused on driver assistance rather than vehicle control; nevertheless, partial and full automation will eventually be important. 4 A wide variety of standard and advanced controls techniques are being applied to road vehicles 4 Vehicles to date have been designed for human control, not automated control. For example, current steering system geometry is designed for “good handling”, i.e. predictable response for humans. The underlying hardware may need to be modified for optimal automatic control.

137 Difficulties 4 Automated control is especially difficult in some situations:  Emergency maneuvers: Control systems optimized for smooth performance at cruise will not work for abrupt maneuvers in emergency situations.  Equipment failure: Special controllers need to be designed to cope with tire blowout or loss of power brakes or power steering.  Heavy vehicles: The load, and the distribution of the load, vary much more for a heavy truck than for a passenger car. Truck controllers need to be much more adaptable than light vehicle controllers.

138 More Difficulties  Low speeds: Engine and transmission dynamics are hardest to model at slow speeds. Applications such as automated snow plows or semi-automated busses will require careful throttle control design.  Low-friction surfaces: As addressed above, it is difficult to predict the effective coefficient of friction on a particular road surface. This affects not only braking performance but also the design of throttle and steering controllers.

139 8.2Actuation 4 Full or partial automation will require actuators, i.e. computer-controlled motors that can move the throttle, brake, and steering. 4 The state of the art is rapidly improving: vehicles are available on the market with electronic fuel injection, electronic power steering, and electronic power brakes, all driven by performance and weight improvements for manually-driven cars. This makes it much easier to add computer control. 4 Special-purpose actuators will still be needed in some applications, such as quick-response throttles for closely-spaced platoons of cars.

140 8.3Driver condition 4 It is important to assess driver alertness, both in a drowsy driver warning system, and in an automated system that is preparing to return control to the driver. 4 Alertness can be sensed indirectly, by watching lane-keeping performance; or directly, by watching for eye blink rate and closure.

141 Perclose Measuring percentage of time eyes are closed. This system illuminates the face with two IR wavelengths, one of which reflects from the retina. Subtracting the images will create a blank image (if the eyes are closed) or an image with two bright spots (if the eyes are open). Top left: image with retinal reflections Top right: no retinal reflections Bottom left: difference image, note two bright dots for reflections

142 8.4Communications 4 Infrastructure-based ITS projects are building roadway- to-vehicle communications for traffic and routing information. 4 Dedicated Short Range Communication (DSRC) is being developed for warning of local conditions, such as ice, sharp curves, changes in speed limit, or stopped traffic out of sight around a bend. 4 Vehicle-vehicle communications will be increasingly important for collision warning systems. The lead vehicle can communicate speed, braking, intent to change lanes, traffic status ahead, etc. 4 In the platoon version of full automation, vehicles need to communicate with low latency, e.g. 20 times / second. This creates interesting research questions on creating local nets, on managing both inter- and intra-platoon communication, and on reliable communications in urban canyons and other difficult environments.

143 Communications Technologies 4 Most communications schemes rely on radio, using a variety of bands. 4 Schemes currently under research include : modulating the radar reflectivity of a surface, so radar- equipped trailing vehicles can get information as well as range powering a transponder with radar energy, again to communicate to a following radar-equipped vehicle modulating LED brake lights so trailing vehicles equipped with detectors tuned to that particular wavelength can pick up information

144 Section 8 Questions: 4 What makes vehicle control difficult? 4 What makes communications difficult?

145 9Sensor-friendly roadways and vehicles 4 On-board sensing would work better if the environment were designed for sensing. 4 Current roadways have significant variability (Bott’s dots, painted lines, thermoplastic stripes, etc). 4 Current roadways have many objects that cause radar “clutter” (returns from objects that are not of interest), such as guard rails, roadside signs, bridge overpasses

146 9.2Path prediction 4 “Path Prediction” refers to estimating where the vehicle’s current lane goes, so an obstacle detection system knows where to look for stopped cars and other obstructions. 4 Sensor friendly systems will improve path prediction by enhancing lane visibility. 4 They will also improve obstacle detection by reducing clutter from off-road objects and increasing returns from other vehicles.

147 9.1Dealing with clutter  Clutter can be:  Moved: Sign posts could be placed farther from the travel lanes.  Masked: Radar Absorbing Material (RAM) could be applied to objects such as bridge abutments  Marked: Polarizing reflectors, or filters that absorb only a narrow frequency band, could be applied to large objects. They would then still appear in a radar return, but would be marked in the radar signal as known fixed objects  Mapped: The locations and signatures of fixed objects could be stored in a map, and provided to individual vehicles.

148 Sensor-Friendly Features 4 Besides clutter suppression, sensor- friendly systems can improve visibility: Lane markings can be improved with pigments that reflect radar or near- visible wavelengths Vehicle visibility can be improved with radar reflectors, either fixed or modulated for communications

149 Microstrip patch retroreflector antenna 4 Without a stable aiming point, radar-based vehicle tracking is difficult. Lead vehicle appears to wander OSU patch retro-reflector provides a distinctive, wideband, vehicle marker. Compact form factor is easily attached to vehicles. Angle-invariant return provides aim-point stability. Wide bandwidth permits good range resolution. Freq. [GHz] Angle

150 Section 9 Questions: 4 List four ways of handling clutter. 4 How can sensor-friendly features help with the path prediction problem?

151 10Comments and conclusions 4 Many of these technologies work best in combination: e.g. lane tracking aids both lane departure and rear-end warnings. 4 Many of these work best with some infrastructure assistance: e.g. lane departure systems need at least good road delineation, and can take advantage of better markings. 4 In many cases, the technology is approaching readiness; the remaining obstacles to deployment are legal and institutional.

152 Acknowledgements 4 My thanks to the CMU Navlab group, and the Automated Highways Tech Team. Much of the research described here was supported by NHTSA and FHWA. 4 Photo credits: thanks to Liang Zhao (stereo), Todd Williamson (stereo), Richard Grace (perclose), Gerald Stone and California PATH (magnets and snowplow), Bill Stone and California PATH (platoon), Colin Ashmore (buried wire), Umit Ozguner, Jon Young, and Brian A. Baertlein (radar reflective surfaces and microstip antenna), K2T Inc (ladar), Dirk Langer (radar), Parag Batavia (driver differences chart), Assistware Technologies (vision system) and Todd Jochem (bus). All pictures copyright by their owners; reproduced by permission.


154 UNIT-V-Vehicle network systems A primary purpose of automotive networked systems is to reduce the amount of wire that is used. 15 kg of wire can be eliminated by the use of networking on a single vehicle For example, systems such as traction control and engine management that make use of the engine speed sensor can make use of a single engine speed sensor by placing the reading on the data bus as required (i.e. the sensor is multiplexed), instead of having a separate sensor for each system. Similar economies are possible with a range of systems and this can result in a reduction in the total number of sensors on a vehicle.


156 There are several areas of vehicle control where data buses can be used to advantage. Some of these, such as lighting and instrumentation systems, can operate at fairly low speeds of data transfer, e.g bits per second. Others such as engine and transmission control require much higher speeds, probably bits per second, and these are said to operate in ‘real time’. To cater for these differing requirements the Society of Automotive Engineers (SAE) recommends three classes known as Class A, Class B and Class C. Class A. Low speed data transmission, up to bits/s, used for body wiring such as exterior lamps etc. Class B. Medium speed data transmission, bits/s up to bits/s, used for vehicle speed controls, instrumentation, emission control etc. Class C. High speed (real time) data transmission, bits/s up to bits/s (or more), used for brake by wire, traction and stability control etc.


158 The system comprises four subsystems. 1. The Lucas EPIC (Electronically-programmed injection control ) system. 2. The Lucas flow valve anti-lock braking system. 3. A clutch management system (CMS). This replaces the normal clutch pedal linkage with a computer controlled, hydraulically actuated system. 4. Adjustable rate dampers are fitted. The damping rate is adjusted by the computer (ECM) to provide optimum damping during rapid steering input, braking and acceleration.

159 Master controller Each of the above systems has a CAN interface, which permits them to be connected to the master controller. A network of twisted pair cables connects each of the above subsystems to the master controller and this allows the transfer of sensor information and control signals with reliable safety checking and minimal wiring. The master controller thus receives information from the subsystems via the CAN bus (cables). The master controller is directly connected to a switch pack (for cruise and damper control), two accelerometers and an inclinometer (for hill detection). This means that the master controller ‘knows’ the complete status of the vehicle and the driver’s requirements. The vehicle status information is processed by the master controller to generate control signals which are sent to the subsystems. These “Master” signals over-ride the normal operation of the subsystems to operate another tier of systems known as the integrated systems. In the event of CAN failure, each subsystem defaults to stand-alone operation.

160 The integrated systems The four subsystems, i.e. EPIC, ABS, damper control and clutch management, are integrated (made to work together) to provide seven additional functions of vehicle management. The computer programs that do this controlling are executed by the master controller. These seven integrated systems are: 1.traction and stability control control 3.power shift 4.engine drag control 5.hill hold 6.damper control 7.centralized diagnostics.

161 These use one or more serial networks to achieve the following objectives: Reduction of the number of wires within the wiring looms of a vehicle; Improved system failure diagnosis; Distributed control centers in or off the vehicle which can talk and interact with one another; Improved manufacturing techniques and increased reliability due to a reduction in the number of wires and connectors


163 1.Space Segment: The space segment of GPS consists of 24 satellites fielded in nearly circular orbits with a radius of 26,560 km, period of nearly 12 hours and stationary ground tracks. The satellites are arranged in six orbital planes inclined at 55° relative to the equatorial plane, with four satellites distributed in each orbit. With this constellation, almost all users with a clear view of the sky have a minimum of four satellites in view. Each satellite receives and stores information from the control segment; maintain very accurate time through on board precise atomic clocks. 2. Control Segment: The control segment of GPS consists of five tracking stations distributed around the earth of which one, located in Colorado Springs, is a Master Control Station. The control segment tracks all satellites, ensures they are operating properly and computes their position in space. The computed positions of the satellites are used to predict where the satellite will be later in time. These parameters are uploaded from the control segment to the satellites and referred to as broadcast ephemeredes. 3.User Segment: The GPS user segment consists of the GPS receivers and the user community. Almost all GPS tracking equipment have the same basic components: an antenna, an RF (Radio Frequency) sections a microprocessor, a control and display unit (CDU), recording device and a power supply. Usually all component, with the exception of the antenna, are grouped together and referred to as a receiver. GPS receivers convert SV signals into position, velocity, and time estimates. Four satellites are required to compute the four dimensions of X, Y, Z (position) and time. GPS receivers are used for navigation, positioning, time dissemination, and other research. 4.GPS Signals: Each GPS satellite continuously broadcasts ranging signals containing wealth of information. The information contained in GPS signals includes the carrier frequencies (L1 & L2), codes (coarse acquisition [C/A] & Precise [P]) and the navigational message. These allow users to measure their pseudo ranges and to estimate their positions in passive, listen only mode.

164 Basic principle of GPS. The basic principle of determining the position by using GPS satellites is based on measurement of distances from the point of observations to the satellite. This is done by comparing the reading of transmitter antenna time with the receiver antenna time. It cannot be assumed that the two clocks will be strictly in synchronization since the clocks used in the present type of receivers are quartz clocks to reduce the cost of the receiver. The observed signal time will have a systematic synchronization error. Since the measured range has got this systematic error in it, the computed distances will also be biased, and therefore, these are called pseudo-range. To compute the position based on this pseudo-range, the error due to time bias has to be corrected and therefore, this is also taken as an unknown and determined before deriving the true range. As we know from the simple formulate of distance computation that R = Ö ((X – X i ) 2 + (Y –Y i ) 2 + (Z –Z i )) 2 Where X, Y & Z are the co-ordinate of the station, therefore unknown and X i, Y i & Z i are the co-ordinates of the satellite, which is broadcast information. To find the true range the time bias t is also has to be considering, therefore R = ((X – X i ) 2 + (Y –Y i ) 2 + (Z –Z i )) 2 + TC Where C is the velocity of light, R is pseudo-range and T is travel time. Now in this equation, there are four unknown therefore, to solve this at least 4 satellites will have to be observed. The minimum requirement in this case is 1.To know the co-ordinates of satellite antenna 2.To know the satellite time at the time of emission of the signal 3.Minimum 4 satellites, 4th one required to determine the time bias.






170 Vehicle Navigation System (VNS) A Vehicle Navigation System (VNS) is a driving assist system that combines digital maps, vehicle position, route optimization, route guidance, and other technologies. It is one of the most important components of advanced traffic and traveler information systems in Intelligent Transportation Systems (ITS) and is an important application and research field in Geographic Information Systems for Transportation (GIS-T).

171 A Framework for Network based VNS A framework for network based VNS is illustrated in Figure. Four components are encompassed in the proposed framework, namely, the content supported layer, the service center, the communication layer, and navigation terminals. 1)The Content Supported Layer 2)The Service Center 3)The Communication Layer 4)Navigation Terminals


173 The integration of traffic information and road network


175 MESSAGE – Mobile Environmental Sensing System Across a Grid Environment 4 Heterogeneous fixed and mobile sensors on infrastructure, vehicles and people 4 Sensors communicate via wireless and wired networks 4 Positioning via GPS + wireless ranging 4 Integration of processing along the data path 4 Multiple application studies in different local contexts Camden Town, London Processing


177 Sensor Network for Traffic Accident Detection and Notification Designing a sensor network that will inform incoming vehicles of these accidents/congestions well in advance so that the drivers of the vehicles may take appropriate actions. Present traffic monitoring systems use expensive devices such as video cameras, magnetic loop detectors that are expensive, difficult to deploy and not very scalable Vehicular network solutions differ greatly in their design, protocol and implementation. As such a vehicle that uses one vehicular solution will not be able to communicate with other vehicles along the road unless they all implement the same solution. This can be a very grave problem

178 Challenges 4 Sensors are very resource-constrained: power, memory, computation. - minimizes resource consumption. 4 Vehicles on highways usually travel at high speeds between 65 to 70 mph. They need to be informed of the accident/congestion up ahead as quickly as possible before it is too late. - designed to sense accidents as soon as they occur and communicate this information to the rest of the relevant network very quickly. 4 Users are often unwilling to learn (or just plain lazy) how to use new systems. - requires minimal interaction with the user and will be perceived as very uncomplicated by the user

179 1. It integrates an ad-hoc sensor network with a vehicular network to create an effective, energy- efficient traffic accident detection and notification system without all of the problems mentioned above. 2. BY introduce the new concept of Virtual Group and Watchdog Group of sensors that will track the motion of a car and will greatly increase the reliability of the network while decreasing the energy-consumption of the sensors. Sensor Network for Traffic Accident Detection and Notification

180 4 Sensors placed along-side highway roads will detect a traffic accident and will communicate this message to sensors further down the road, which will in turn notify incoming vehicles of the accident up-ahead. Assumptions: 1. Highways 2. Unidirectional traffic 3. Vehicles are equipped with bi-directional radios that can do two things: i. Transmit alarm message when accident occurs. ii. Receive notification of accident broadcast by sensor.

181 1. Watchdog Groups: Sensors are divided into groups of n each, say three sensors S1, S2 and S3. When there is no traffic on the highway, in each group one sensor (S1) will be on for a certain fixed period of time while the other two (S2 and S3) remain off. After this fixed period S2 will wake up and S1 and S3 will sleep and so on. Synchronized timers will be used to control the sleep/wake cycle of sensors in each group.

182 Watchdog Group n = 3 Watchd og group 1 Watchd og group 2 awakeasleepawakeasleep awakeasleepawakeasleepawake

183 2. Virtual Groups: Sensors are again divided into groups of n each. But in this case, the group is not “fixed” but rather “moves” along the highway following the motion of the vehicle being sensed.

184 Virtual Group n = 3 Virtual Group

185 4 Normal Operation: - Car approaches junction. - Special sensor (always on) at junction detects car, alerts closest neighboring sensor, S1. - S1 will alert S2, S2 will alert S3. Now S1, S2 and S3 will be awake (Virtual Group 1).

186 Normal Operation Special Sensor Virtual group

187 Accident Occurs: - Detection of accident: Air-bag trigger in cars that detects the accident will trigger the car radio to broadcast accident alarm message. - uses air-bag triggers because: i. It provides greater accuracy in detecting actual accidents and not just false alarms. ii. It simplifies the work of the sensors (lesser sensing, lesser computation). ii. Air-bag triggers are already present in vehicles; does not require additional add-ons. - The sensor closest to the car that receives the alarm message will wake up the sensors behind it (if they are already not awake). - The sensor will then broadcast an Event Notification message with the TTL field set to a fixed value so that the message does not propagate further than is required.

188 Case Accident

189 Special Cases 1. Very long stretch of highway with no exits: - Accident occurs. - Vehicle must be informed before it leaves all exits behind. - To relay message from one sensor to next until it reaches car will be too slow. - Use access point to convey message directly to sensor closest to next-to-last exit (as far in advance as feasible). - Sensor will inform vehicle before it reaches last exit and looses all chances to re-route.

190 Very long stretch of road w/no exit Long stretch of road with no exit

191 Special Cases contd. 2. Backup Case - In case of sensor failure: - Normally sensors communicate with each other on a per-hop basis. - If a sensor goes down, its immediately neighboring sensors on both sides will increase their sensing and communication range. - The increase in power consumption is a small price to pay for greater reliability.

192 Backup Case n = 3

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