Concept of Operations and 

Voluntary Operational Requirements 

for 

Forward Collision Warning Systems (CWS) 

 and 

Adaptive Cruise Control (ACC) Systems 

 On-board Commercial Motor Vehicles 

. 

 

July 2005 
Foreword 

The Federal Motor Carrier Safety Administration’s (FMCSA’s) safety goal is to reduce the 

number and severity of large truck fatalities and crashes. During the last several years, FMCSA 

has collaborated with the trucking industry to test and evaluate several on-board safety systems 

for commercial motor vehicles to increase the safety and security of all roadway users. FMCSA 

is now promoting voluntary adoption of these systems within trucking fleets by initiating steps to 

work closely with the trucking industry to define vendor-independent, voluntary requirements. 

The purpose of this document is to relay a better understanding of the functions of on-board 

safety systems for vehicle stability and to provide insight into the safety and efficiency benefits 

of using the systems. This document describes the concept of operations and voluntary 

requirements for Collision Warning Systems and Adaptive Cruise Control (ACC) systems for 

large trucks greater than 10,000 pounds gross vehicle weight rating (GVWR). Concepts of 

operations provide information about how each user interacts with these safety systems and 

their operational conditions. Voluntary requirements describe features and functions used to 

define the safety systems and their operational functionality. The information has been 

developed in collaboration with trucking industry stakeholders, including representatives from 

manufacturers, insurance companies, commercial vehicle carriers, drivers and academia. 

The results from this project can be used by motor carriers as system guidelines for voluntary 

adoption of on-board safety systems within their trucking fleets. 

This is a final report developed under FMCSA’s deployment of on-board safety system program. 

It does not supersede an earlier report on the subject. 

Notice 

This document is disseminated under the sponsorship of the Department of Transportation in 

the interest of information exchange. The United States Government assumes no liability for its 

contents or use thereof. 

This report does not constitute a standard, specification, or regulation. 

The United States Government does not endorse products or manufacturers. Trade or 

manufacturers' names appear herein only because they are considered essential to the object 

of this document. 

ii
Acknowledgements 

FMCSA wishes to acknowledge the efforts of those in the government, academia, research 

institutions and industry who contributed their knowledge and expertise to this effort. Those 

individuals include Carl Kirk and Robert Braswell of the Technology and Maintenance Council; 

Marty Fletcher of US Xpress; Jim Kennedy of McKenzie Tanklines; Ron Knipling, PhD of the 

Virginia Tech Transportation Institute; Scott Claffey of Great West Insurance Company; Dave 

Melton of Liberty Mutual Research Institute for Safety; Anne McCartt, PhD of the Insurance 

Institute for Highway Safety; Rick Craig of the Owner Operators Independent Drivers 

Association; Bill Gouse of the American Trucking Associations; Tom Moses of the Spill Center; 

Bob Interbitzen of the National Private Truck Council; Mike Formica and Dean Pomerleau, PhD 

of Assistware; Bill Patrolia of Iteris; Meny Benady of Mobileye; Kevin Romanchok, Jim Szudy, 

and Richard Beyer of Bendix; Alan Korn, Richard Romer, and Mike Lambie of Meritor WABCO; 

Greg Shipman of Delphi; Tom Mattox of Eaton VORAD; Skip Yeakel of Volvo; Charlie Groeller 

of Mack Trucks; Paul Menig of Freightliner; and Dan Murray of the American Transportation 

Research Institute. 

iii
iv

Technical Report Documentation Page 

1. Report No. 

FMCSA-MCRR-05-007 

2. Government Accession No. 3. Recipient's Catalog No. 

5. Report Date 

July 2005

4. Title and Subtitle 

Concept of Operations and Voluntary Operational Requirements for Automated Cruise 

Control/Collision Warning Systems (ACC/CWS) On-board Commercial Motor Vehicles 

6. Performing Organization Code 

7. Author(s) 

Amy Houser (FMCSA), John Pierowicz (Calspan Corp.), Roger McClellan (Calspan 

Corp.) 

8. Performing Organization Report No. 

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) 

Calspan Corporation 

4455 Genesee Street 

Buffalo, NY 14225 

11. Contract or Grant No. 

DTMC75-03-F-00087 

13. Type of Report and Period Covered 

Technical Report – October 2003-July 2005 

12. Sponsoring Agency Name and Address 

Federal Motor Carrier Safety Administration 

Office of Research and Analysis 

400 Virginia Ave. SW 

Washington, DC 20024 14. Sponsoring Agency Code 

FMCSA 

15. Supplementary Notes 

This program was administered through the Federal Motor Carrier Safety Administration (FMCSA). The FMCSA Program Manager is Mrs. 

Amy Houser. 

16. Abstract 

The Federal Motor Carrier Safety Administration’s (FMCSA’s) safety goal is to reduce the number and severity of large truck fatalities and 

crashes. During the last several years, FMCSA has collaborated with the trucking industry to test and evaluate several on-board safety 

systems for commercial motor vehicles to increase the safety and security of all roadway users. FMCSA is now promoting voluntary adoption 

of these systems within trucking fleets by initiating steps to work closely with the trucking industry to define vendor-independent, voluntary 

requirements. 

The purpose of this document is to relay a better understanding of the functions of on-board safety systems and to provide insight into the 

safety and efficiency benefits of using the systems. The information has been developed in collaboration with trucking industry stakeholders, 

including representatives from manufacturers; insurance companies; commercial motor vehicle carriers; drivers; and academia. 

This document describes the concept of operations and voluntary requirements for Automated Cruise Control/Collision Warning Systems 

(ACC/CWS) for large trucks greater than 10,000 pounds gross vehicle weight rating (GVWR). Concepts of operations provide information 

about how each user interacts with these safety systems and their operational conditions. Voluntary requirements describe features and 

functions used to define the safety systems and their operational functionality. 

17. Key Word 

Automated Cruise Control, Collision Warning Systems, Commercial 

Motor Vehicles, Heavy Trucks, Safety Systems, Tractor-Trailers, 

Vehicle Stability Systems 

18. Distribution Statement 

19. Security Classif. (of this report) 

Unclassified 

20. Security Classif. (of this page) 

Unclassified 

21. No. of Pages 

24 

22. Price 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
v 

SI* (MODERN METRIC) CONVERSION FACTORS 

APPROXIMATE CONVERSIONS TO SI UNITS APPROXIMATE CONVERSIONS FROM 

Symbol When You Know Multiply By To Find Symbol Symbol When You Know Multiply By 

LENGTH LENGTH 

in inches 25.4 millimeters mm mm millimeters 0.039 incft feet 0.305 meters m m meters 3.28 feeyd yards 0.914 meters m m meters 1.09 Yami miles 1.61 kilometers km km kilometers 0.621 mil

AREA AREA 

in2 square inches 645.2 square millimeters mm2 mm2 square millimeters 0.0016 squft2 square feet 0.093 square meters m2 m2 square meters 10.764 squyd2 square yards 0.836 square meters m2 m2 square meters 1.195 squac acres 0.405 hectares ha ha hectares 2.47 acrmi2 square miles 2.59 square kilometers km2 km2 square kilometers 0.386 squ

VOLUME VOLUME 

fl oz fluid ounces 29.57 milliliters ml ml milliliters 0.034 fluigal gallons 3.785 liters l l liters 0.264 gaft3 cubic feet 0.028 cubic meters m3 m3 cubic meters 35.71 cubyd3 cubic yards 0.765 cubic meters m3 m3 cubic meters 1.307 cub

MASS MASS 

oz ounces 28.35 grams g g grams 0.035 oulb pounds 0.454 kilograms kg kg kilograms 2.202 poT short tons (2000 lbs) 0.907 megagrams Mg Mg megagrams 1.103 sho

TEMPERATURE (exact) TEMPERATURE (exact) 

°F Fahrenheit 5(F-32)/9 Celsius °C °C Celsius 1.8 C + 32 

temperature or (F-32)/1.8 temperature temperature 

ILLUMINATION ILLUMINATION 

fc foot-candles 10.76 lux lx lx lux 0.0929 fl foot-Lamberts 3.426 candela/m2 cd/m2 cd/m2 candela/m2 0.2919 

FORCE and PRESSURE or STRESS FORCE and PRESSURE or ST

lbf pound-force 4.45 newtons N N newtons 0.225 psi pound-force per square inch 6.89 kilopascals kPa kPa kilopascals 0.145 

* SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380.
1 

1. INTRODUCTION 

The Federal Motor Carrier Safety Administration’s (FMCSA’s) safety goal is to reduce the 

number and severity of large truck fatalities and crashes. During the last several years, FMCSA 

has collaborated with the trucking industry to test and evaluate several on-board safety systems 

for commercial motor vehicles to increase the safety and security of all roadway users. FMCSA 

is now promoting voluntary adoption of these systems within trucking fleets by initiating steps to 

work closely with the trucking industry to define vendor-independent, voluntary requirements for 

these systems. 

The purpose of this document is to relay a better understanding of the functions of on-board 

safety systems and to provide insight into the safety and efficiency benefits of using the 

systems. The information has been developed in collaboration with expert panels consisting of 

trucking industry stakeholders, including representatives from manufacturers, insurance 

companies, commercial motor vehicle carriers, drivers, and academia. 

This document describes the concept of operations and voluntary requirements for Forward 

Collision Warning Systems (CWS) and Adaptive Cruise Control (ACC) systems for large trucks 

greater than 10,000 pounds gross vehicle weight rating (GVWR). Concepts of operations 

provide information about how each user interacts with these safety systems and their 

operational conditions. Voluntary requirements describe features and functions used to define 

the safety systems and their operational functionality. 

This document discusses CWS and ACC systems provided by manufacturers, such as: 

• Delphi Electronics and Safety 

• Eaton VORAD 

• Mobileye 

Descriptions of these currently available systems are in Appendix A. United States Department 

of Transportation (USDOT) websites that contain further information on governmental research, 

testing and evaluation of CWS and ACC systems include: 

www.its.dot.gov/ivi/ivi.htm 

www.fmcsa.dot.gov/safetyprogs/research/researchpubs.htm

2. CONCEPT OF OPERATIONS 

Description – Forward Collision Warning Systems 

CWS are in-vehicle electronic systems that monitor the roadway in front of the host vehicle and 

warn the driver when a potential collision risk exists. For example, currently available radarbased CWS use algorithms to interpret transmitted and received radar signals to determine 

distance, azimuth, and relative speed between the host vehicle with the CWS and the vehicle or 

object ahead of it in the lane. When the host vehicle is traveling along the roadway, the CWS 

can warn the driver when a vehicle or object is in its lane within a predefined closing time 

threshold. Currently, CWS do not take any automatic action to avoid a collision or to control the 

vehicle; therefore, drivers remain responsible for the safe operation of their vehicles using both 

steering and braking, if safe to do so, to avoid a crash. As the time interval to the vehicle ahead 

decreases, CWS issue a progressively more urgent warning. The system’s beam width/field of 

view forms an isosceles triangle with its apex at the front center of the vehicle. As an object gets 

closer to the front of the vehicle, a different range or time interval is reached, and the system 

issues a different type of alarm. The system manufacturers set these warning thresholds. 

Figure 1 illustrates these progressive thresholds. CWS also warn the driver if the system 

malfunctions. CWS may be integrated with ACC systems. 
Figure 1 

CWS Object Detection Ranges and Collision Warning Thresholds 

Description – Adaptive Cruise Control Systems 

ACC systems are in-vehicle electronic systems that automatically maintain a minimum following 

interval to a lead vehicle in the same lane. The ACC system utilizes components of the collision 

warning system and a conventional cruise control system. When the host vehicle with the ACC 

system is traveling above a minimum speed threshold, the ACC system controls the engine 

throttle, and if available, engine brake and automatic transmission to maintain the following 

interval. The driver can set and adjust his following interval. In the absence of a vehicle ahead, 

the ACC system operates like a conventional cruise control by maintaining the speed set by the 

driver. The ACC system will notify the driver if the system detects a malfunction. Figure 2 

illustrates the general thresholds used by an ACC system. The system's beam width/field of 

view forms an isosceles triangle with its apex at the front center of the vehicle. It graphically 

displays minimum and maximum following distance or time intervals in which the system 

operates. 

Although ACC systems automatically take action to control the vehicle’s speed, they may not 

sufficiently decelerate the vehicle in all circumstances to avoid a crash. Depending on the 

vehicle load, road grade, and vehicle performance parameters, the level of deceleration control 

typically used by the system is limited to a range between 0.1 and 0.2 g, where g is a unit of 

force equal to the force exerted by gravity. As a result, drivers remain responsible for the safe 

operation of their vehicles, and they should use steering and apply the service brakes, if safe to 

do so, to avoid a crash. 

 

 

3 
 Figure 2 

ACC System Vehicle Following Intervals 

Crash Prevention 

CWS and ACC systems can help reduce crashes when vehicles are equipped with these 

systems. In particular, these systems may prevent rear-end crashes and forward impact 

crashes with objects in the travel lane. These systems may also reduce the impact speed and 

the crash severity. This section describes these crash types. 

• Rear-end Crash – Rear-end crashes occur when the front of a following vehicle 

strikes the rear of a lead vehicle. Data derived from the 2003 General Estimates 

System1

 (GES) indicates that 42,800 rear-end crashes involving large trucks 

occurred in 2003, resulting in 290 fatalities. “In 18 percent of all rear-end crashes 

where the truck was the striking vehicle, there were three or more vehicles involved 

in the crash. The difference is even greater in fatal rear-end crashes. Almost 46 

percent of fatal rear-end truck-striking crashes involved three or more vehicles, 

while only 16 percent of fatal truck-struck rear-end crashes involved three or more 

vehicles. The large difference between the mass of trucks and the mass of other 

vehicles may explain this phenomenon. A typical loaded tractor semi-trailer has a 

gross weight of 80,000 pounds, while most cars weigh less than 4,000 pounds. 

Striking a passenger vehicle in the rear will not bring a heavy truck to a stop or 

even slow it appreciably. Thus, the impact itself does relatively little to keep the 

truck from continuing on and involving other vehicles.”2

 CWS can reduce the risk of 

 

1

 The General Estimates System is directed by the National Center for Statistics and Analysis, which is a component 

of The Office of Research and Development in NHTSA. Data for GES come from a nationally representative sample 

of police reported motor vehicle crashes of all types, from minor to fatal. The system began operation in 1988, and 

was created to identify traffic safety problem areas, provide a basis for regulatory and consumer initiatives, and form 

the basis for cost and benefit analyses of traffic safety initiatives. The information is used to estimate how many motor 

vehicle crashes of different kinds take place, and what happens when they occur. 2 Craft, Ralph. FMCSA Paper: Rear-End Large Truck Crashes, 2002. 

4 
5 

 

these rear-end crashes by identifying fast closing situations and providing the 

driver with additional time to react. ACC systems function to maintain a driver-set 

following interval behind another vehicle, thereby providing more time to resolve 

driving conflicts to reduce the probability of a rear-end collision. 

• Forward Impact with Objects in Travel Lanes – These crashes occur when a 

vehicle strikes an object that is in the vehicle’s travel lane. Data from the 2003 

GES indicates that large trucks were involved in 18,000 crashes of this type in 

2003, resulting in 160 fatalities. CWS can reduce the risk of these crashes by 

warning the driver of the presence of these objects, thereby allowing them 

additional time to take the appropriate avoidance maneuvers. 

Additional benefits of ACC systems and CWS may include the reduction of hard braking events. 

Operations and Users 

This section describes how drivers, fleet managers, and fleet maintenance personnel interact 

with CWS and ACC systems and potential benefits that each stakeholder may realize with these 

systems. 

The commercial vehicle population is comprised of a wide variety of vehicle types and uses. At 

a high level, two types of vehicles are predominant, combination vehicles (tractors-trailers) and 

straight trucks. These two types of vehicles have very different operating characteristics. In 

general, straight trucks tend to be used in a more local setting, used to provide deliveries of 

goods and services to customers generally within a 50 to 100 mile radius of their base of 

operations, while combination vehicles are more often utilized in regional and long distance 

applications. Combination vehicles account for about 30% of total commercial vehicles, but 

65% of the commercial vehicle miles traveled. Due to their high mileage exposure and severity 

of crashes, combination-unit trucks have the highest crash cost per vehicle over the operational 

life of the vehicle.3

 Therefore, CWS may provide a relatively higher safety benefit for operators 

of this class of trucks. 

The trucking industry is actually a broad collection of many industries, each with operating 

characteristics as diverse as the industries they service. Segmentation of the trucking industry is 

often based on the size of fleets, the geographic range of its operations, and the commodities 

hauled. Usually one characteristic is not adequate to describe a particular segment, but rather 

combinations of characteristics are required to best describe operations. For example, there 

may be a trucking firm with a large fleet providing package delivery type service to a relatively 

small geographic area, while there may be a single truck company that provides general freight 

services to all states in the continental United States. 

The movement of goods by truck is conducted on all types of roads, at all hours of the day, and 

in all types of driving conditions. Since collisions with other vehicles or obstacles can occur 

along any route, many fleet types may benefit from using CWS, yet they may be most promising 

for trucks with high mileage accumulated over their operational life or that operate under 

conditions that may present driving challenges such as nighttime or limited visibility due to 

weather. Also, currently, CWS operate at any vehicle speed. ACC systems only operate above 

a specified minimum vehicle speed, which typically limits the systems’ use to roadways where 

drivers travel at or above this minimum speed in accordance with the posted speed limits. The 

application of these systems to specific fleets may be determined by the amount of time the 

fleet’s vehicles operate in these roadway types. 

3 Wang, J.S.; Knipling, R.R.; and Blincoe, L.J. The dimensions of motor vehicle crash risk. Journal of Transportation 

and Statistics. Volume 2, No. 1, pp. 19-43, ISSN 1094-8848, May 1999. 
6 

 

Drivers 

Drivers are the primary CWS and ACC system users, as described in the following daily 

operational scenarios: 

Normal system startup operation – When the driver turns the ignition switch to start the 

vehicle, CWS and ACC systems perform a power-up self-test. The driver scans the warning 

indicators to determine any system malfunctions. If necessary, the driver may alert fleet 

maintenance personnel for corrective action. A driver can scan the CWS or ACC system 

status indicator to verify that the system operation has commenced. 

System fault conditions – If a system fault occurs or the system cannot detect vehicles 

ahead or control the speed of the host vehicle, the driver is provided with a message via the 

system status indicator. Some CWS and ACC systems may display warning indicators 

relating to specific faults or other detected conditions. 

Progressive CWS warning/alert situations – When traveling at or above the minimum 

CWS detection speed, the host vehicle will encounter other vehicles ahead within the travel 

lane. As the host vehicle approaches the vehicle ahead, the CWS may provide a series of 

progressive alerts to the driver. These progressive alerts indicate that the following interval 

is decreasing and the driver should take action. These progressive warnings can escalate 

from audio tone only to audio, visual, or other warning modes. 

ACC system operation – ACC systems automatically maintain a minimum following interval 

between the driver’s vehicle and the vehicle ahead of it. When no vehicle is present in front 

of the vehicle with the ACC system, the ACC system maintains the speed set by the driver 

as in current cruise controls. The system has a self-diagnosis mode that can detect system 

faults. If the system is active when a fault is detected, the ACC system reverts to manual 

throttle control.

On-road use of CWS and ACC systems – A driver may encounter several types of 

roadways where these systems provide a potential benefit. Yet, some systems may have 

limitations, including false positive indications, such as the identification of signs, barrels, 

and other roadside objects that may not be actual obstacles in the travel lane. 

Divided highways and interstates/Straight and large radius curved flat roads – 

“Trucks Involved in Fatal Accidents (TIFA) and GES data show that rear-end truck 

crashes are more likely to occur on divided roadways and interstate highways–

overlapping categories–than other truck crashes. With regard to fatal crashes, 58 

percent of truck striking crashes occurred on interstate highways, as opposed to 19 

percent of all truck fatal crashes.4

” These road types are where CWS and ACC systems 

could provide the greatest benefit. While the vehicle is operating on these roads, CWS 

can detect vehicles ahead and issue warnings to the driver when it detects an excessive 

closing speed condition. ACC systems will control the speed of the host vehicle and 

interval to the lead vehicle. 

Two-way roads with sharp curves – CWS and ACC systems could have limited 

azimuthal coverage to the front of the vehicle. When the host vehicle is traversing sharp 

curves, the lead vehicles may no longer be in the range of the host vehicle’s sensor 

coverage area. When these situations arise, each system has a different means of 

accommodating the loss of detecting the lead vehicle. CWS may not re-detect the lead 

vehicle until the host vehicle enters the curve. The ACC system will revert to 

4

Craft, Ralph. FMCSA Paper Rear-End Large Truck Crashes. 
7 

 

conventional cruise control by maintaining the current set speed until the lead vehicle is 

detected again. When the lead vehicle is detected, the ACC system will revert to the set 

following interval. 

Roads with hills and valleys – CWS may produce false positive indications when the 

host vehicle is on a roadway with major changes in elevation. When a host vehicle is 

traveling up a hill, current CWS may detect objects such as overhead signs. Other 

roadway features that could cause loss of vehicle tracking or false alarms include dips in 

the roadway and hillcrests. 

Fleet Management 

Fleet managers are responsible for all administrative, financial, and operational aspects of the 

fleet. Safety officers focus on the fleet’s operational safety issues and examine the safety 

aspects of the fleet’s vehicles in accordance with USDOT safety regulations. They also work 

with drivers to provide safety and operational training, verify that drivers are complying with 

safety regulations, and examine how well drivers operate their vehicles (e.g., logging accidents, 

traffic infractions, etc.). 

These personnel examine various types of available safety equipment, evaluate the equipment, 

justify the purchase of all equipment, determine the overall effectiveness of this equipment, and 

calculate the return on investment (ROI) for their fleet. They work with the maintenance 

department and drivers to explain CWS and ACC system benefits. CWS and ACC systems 

may have the capability to store operational data internally for retrieval by the fleet. This data 

may be useful in reconstructing an accident or as training feedback in analyzing a driver’s 

performance. Fleet managers may obtain operational data (e.g., number of hard-braking 

events) from CWS and ACC systems via the in-vehicle network and analyze the data to 

determine any systemic problems with their fleet operations (e.g., disproportionate number of 

close-following events with certain drivers, high number of hard-braking events on certain 

routes). These in-vehicle networks provide a data “backbone” to the truck, permitting the 

sharing of various system level data, such as engine and transmission performance. Research 

has indicated that the monitoring of driver behavior can have a positive effect on driver and fleet 

safety.5

 

Maintenance Management and Installation 

Maintenance managers and service technicians are responsible for the proper functioning of all 

equipment installed on the fleet’s vehicles and for installing and maintaining CWS and ACC 

systems on the fleet. The maintenance managers support fleet operations by maintaining CWS 

and ACC systems. They acquire and relay operational and reliability data to the fleet managers 

and work with suppliers to resolve any problems encountered with system use. 

CWS and ACC systems have different installation requirements for each vehicle type and 

model. Depending on the system, CWS and ACC systems may be installed by a truck original 

equipment manufacturer (OEM) or as an aftermarket accessory by the fleet or other service 

personnel. When installed by a truck OEM, the CWS and ACC system component locations 

and mounting methods are identical for each vehicle model. The OEM provides dedicated 

wiring harnesses for the connection between the CWS and ACC systems and the vehicle. 

When installed as an aftermarket accessory, CWS and ACC systems’ components should be in 

5 Knipling, R.R.; Boyle, L.N.; Hickman, J.S.; York, J.S. Daecher; C., Olson, E.C.B.; and Prailey, T.D. Synthesis 

Report # 4: Individual Differences and the High-Risk Commercial Driver. Project Final Report, Transportation 

Research Board Commercial Truck and Bus Synthesis Program. ISSN 1544-6808, ISSN 0-309-08810-0, 

available at http://trb.org/news/blurb_browse.asp?id=11, 2004 
8 

the proper locations and orientations as described in the installation manual with the key 

parameters entered into the system. Furthermore, the systems will require periodic 

maintenance, particularly in the area of component (e.g., radar, camera, antennae) alignment. 

3. VOLUNTARY REQUIREMENTS 

The voluntary requirements included in the following sections define fundamental CWS and 

ACC system features and the ability of the systems to withstand the electrical and 

environmental extremes commonly found on commercial vehicles. 

The types of voluntary requirements for CWS include: 

1. Functional Requirements 

2. Data 

3. Hardware and Software Requirements 

4. Driver Vehicle Interface (DVI) Requirements 

5. Maintenance and Support Requirements 

CWS and ACC system manufacturers may include additional functions to augment system 

capability and features that may be useful beyond minimum system functionality; the operational 

features that fall into this category are labeled with the term “OPTIONAL”. However, in all 

cases, CWS and ACC systems must comply with all existing FMCSA Safety Regulations. The 

requirements numbering system designates defining requirements with an “R” and optional 

features with a “T”. 

3.1 Functional Requirements 

Functional requirements refer to basic system functionality and operation of CWS and ACC 

systems. 

R1-1 CWS and ACC systems should perform a self-test that checks all major 

system sensors and components and operate within 30 seconds of starting 

the vehicle. System status results should be provided to the driver within the 

30 seconds time interval. 

R1-2 CWS should detect, track, and issue warnings for the following potential precollision conditions based on following interval thresholds when the functional 

requirements R1-3 and R1-4 are met: 

• Host vehicle closing on a lead vehicle with constant velocity 

• Host vehicle closing on a lead vehicle that is accelerating 

• Host vehicle closing on a lead vehicle with both vehicles decelerating 

• Host vehicle closing on a lead vehicle preceded by a lane change 

• Host vehicle closing on a stopped lead vehicle 

• Host vehicle closing at a constant speed on a decelerating lead 

vehicle 

• Host vehicle closing on a stationary object in the roadway 
9 

R1-3 CWS and ACC systems should be capable of detecting a vehicle in the travel 

lane of the vehicles with the CWS and ACC systems to a distance of up to 

100 meters (328 feet) on straight roads and on curves with radius greater 

than 500 meters (1640 feet). 

R1-4 CWS and ACC systems should be capable of differentiating between 

oncoming traffic on two-way curved roadways and vehicles in the travel lane 

of the vehicles with the CWS and ACC systems. 

R1-5 CWS and ACC systems should function under all potential weather 

conditions such as clear weather, rain, snow, fog, or combinations of these 

conditions. If the system cannot function in these conditions, the driver 

should be provided with a clear indication that the system is not functioning. 

R1-6 CWS and ACC systems should be capable of differentiating stationary 

roadside objects such as guardrails, signs, and bridges from moving vehicles 

in both the travel lane and opposing lanes of the vehicles with the CWS and 

ACC systems. 

R1-7 If CWS and ACC systems engage the vehicle’s service brakes, the vehicles 

brake lights should be activated in compliance with Federal Motor Vehicle 

Safety Standard 108. 

R1-8 CWS should use progressive warnings to provide the driver with sufficient 

time to avoid forward crashes. 

T1-1 OPTIONAL – CWS may interact with an ACC system to maintain a safe 

following interval to the vehicle ahead. 

T1-2 OPTIONAL – CWS may issue proximity warnings when the host vehicle is 

slowly moving forward (less than 2 mph) towards a stationary object or if an 

object ahead is slowly rolling towards the front of the host vehicle. 

3.2 Data 

This section defines the format of data generated by or can be obtained directly in real-time 

from CWS and ACC systems. Two Society of Automotive Engineers (SAE) standards specify 

in-vehicle data communication in heavy trucks: 

• SAE J1587, “Electronic Data Interchange between Microcomputer Systems in HeavyDuty Vehicle Applications” (message definition for the J1708 data bus), or 

• SAE J1939-71, “Recommended Practice for Control and Communications Network for 

On-Highway Equipment – Vehicle Application Layer” 

Although neither of these standards defines CWS messages, it would be beneficial if CWS 

suppliers adopt a common set of standard CWS messages. Drivers and fleet managers could 

obtain these CWS messages via the in-vehicle data network. SAE J1939-71 already defines 

the data available from ACC systems via the on-board diagnostic (OBD) connector. 

T2-1 OPTIONAL – ACC systems may issue various data messages about the 

operating states and modes of the system on the in-vehicle data network, 

which may be custom messages or as defined by SAE standard J19396

. 

T2-2 OPTIONAL – CWS and ACC systems may have the capability to store 

operational data for providing driving feedback to drivers. 

 

6

 Heavy trucks may have either or both J1708 and J1939 networks. J1708 (J1587) is typically more easily accessible 

by the fleet, and J1939 is typically reserved for high-priority engine-transmission control data. However, CWS may 

interface with either or both networks. See Section 4.4 for a listing of CWS’ network messages. 
3.3 Hardware and Software Requirements 

Hardware and software requirements deal directly with the detailed functionality of the 

hardware, environmental and electrical concerns, mounting/installation issues, and software 

design. Figures 3 and 4 illustrate the major functional components and interfaces of CWS and 

ACC systems as described in the following sections, respectively. Figure 3 shows the interrelationship of the CWS components. The electronic control unit (ECU) accepts data from the 

forward-looking sensor. Through the vehicle network (J1708 or J1939), the ECU monitors the 

brake activation status and engine power. The output of the system is a status indicator and, 

when necessary, a warning, which appear on the driver-vehicle interface. Figure 4 shows the 

inter-relationship of the ACC system components. The ECU has the same input and outputs as 

in a CWS, but it has the additional capability to control the engine speed or to shift the automatic 

transmission. Both figures show that the CWS and ACC are often integrated into a single 

system. 

Figure 3 

CWS Major Functional Components 

Figure 4 

ACC System Major Functional Components 

10 
11 

Typical System Hardware 

This section describes the functionality of the primary physical components of CWS and ACC 

systems. They refer to the functional blocks shown in Figures 3 and 4. 

R3-1 Forward-looking Sensor or Detector – CWS and ACC systems should 

have a sensor or apparatus that detects vehicles in the front of the host 

vehicle. This sensor or apparatus should be capable of determining the 

distance and location of moving or stationary vehicles in the travel lane of the 

host vehicle. CWS and ACC systems should be capable of detecting moving 

or stationary vehicles to at least 100 meters (328 feet) ahead of the vehicle. 

R3-4 Electronic Control Unit (ECU) – The CWS and ACC systems’ ECU should 

be used to gather data for calculating key parameters to provide warnings. 

For the ACC system, the ECU should be capable of controlling the engine 

speed or shifting the automatic transmission. 

R3-2 Driver Vehicle Interface – CWS and ACC systems should provide a driver 

vehicle interface (DVI) to permit the driver to interact with the systems. A DVI 

consists of controls and indicators for CWS and ACC systems related to the 

system operation. The DVI includes progressive audible and visual warnings 

of a potential collision threat to the host vehicle. CWS and ACC systems 

should provide a visual indication of the status of the systems. System status 

includes operational/non-operational, tracking/not-tracking, and system fault 

conditions. See Section 3.4 for complete DVI requirements. 

T3-1 OPTIONAL – Adaptive Cruise Control – CWS may interact with an ACC 

system to maintain a safe following interval between the host vehicle and the 

vehicle in front of it. 

T3-2 OPTIONAL – Vehicle Network – CWS and ACC systems may use the invehicle data network (SAE J1708 or J1939) for data communication to data 

recording or diagnostic devices. 

Environmental Requirements 

The environmental conditions that exist in heavy trucks are very severe. The SAE has 

developed a comprehensive standard that describes various aspects of the heavy truck 

environment in its J1455 standard. The standard also includes procedures that are used to 

verify system compliance. 

R3-3 CWS and ACC systems should meet the environmental requirements as 

stated in the most recent version of the following SAE standard: 

SAE Standard J1455, “Joint SAE/Technology and Maintenance Council 

(TMC) Recommended Environmental Practices for Electronic Equipment 

Design (Heavy-Duty Trucks)”. 

The following environmental aspects are covered by the standard: 

• Altitude 

• Fungus 

• Mechanical Shock 

• Mechanical Vibration 

• Relative Humidity 

• Temperature 

• Salt Spray Atmosphere 

• Immersion and Splash 

• Steam Cleaning and Pressure Washing 

• Dust, Sand, and Gravel Bombardment 
12 

Electrical Requirements 

In a truck’s electrical power distribution system, the system voltage may vary, the alternator may 

generate electrical noise, and various types of transients may momentarily place more than 100 

volts direct current (VDC) on the electrical distribution system’s wiring. In addition, there may be 

electrostatic discharge into the system from a buildup of static electricity. Because CWS and 

ACC systems connect to the truck’s electrical power distribution system, they should function 

normally throughout all of these perturbations without damage. 

R3-4 CWS and ACC system power should be derived from the vehicle electrical 

system. 

R3-5 CWS and ACC systems should meet the electrical requirements as stated in 

most current version of the following SAE standards: 

SAE Standard J1455, “Joint SAE/TMC Recommended Environmental 

Practices for Electronic Equipment Design (Heavy-Duty Trucks)”. 

SAE Standard J1113, “Electromagnetic Compatibility Measurement 

Procedures and Limits for Vehicle Components (Except Aircraft) (60 Hz to 

18 GHz)”. 

The following environmental aspects are covered by the standards: 

• Steady State Electrical Characteristics 

• Transient Electrical Characteristics 

• Electromagnetic Susceptibility 

• Electromagnetic Emission 

R3-6 CWS and ACC system data should not be destroyed nor corrupted during a 

power surge. 

Mounting and Installation Requirements 

Mounting and installation requirements include all aspects related to the installation of CWS and 

ACC system hardware onto the truck, including the mounting of the individual system 

components. There are no specific requirements pertaining to system size or weight. 

R3-7 CWS and ACC systems should be installed per manufacturer’s 

recommendations. 

R3-8 Major CWS and ACC system components, other than cabling or small 

mounting components, should be marked with the manufacturer’s 

identification. 

Software Requirements 

Software requirements refer to the embedded software that runs in CWS and ACC systems and 

controls all system functionality. The microcontroller or microprocessor continuously runs the 

system software when CWS and ACC systems are active. 

T3-3 OPTIONAL – CWS and ACC systems may include software for downloading 

ASCII data files that can be easily read into a statistical, database, or 

spreadsheet software package. 

T3-4 OPTIONAL – The embedded software of CWS and ACC systems can be 

field upgradeable via the in-vehicle network connection (i.e., J1587 or J1939) 

or other common data interface (e.g., RS-232 or Universal Serial Bus (USB)). 
13 

Only authorized personnel should upgrade embedded software. 

3.4 Driver-Vehicle Interface Requirements 

These requirements define specific ways in which CWS and ACC systems interface with the 

driver (i.e., Driver-Vehicle Interface), and include indicators, displays, and warning methods. 

The National Highway Traffic Safety Administration (NHTSA) Federal Motor Vehicle Safety 

Standard 101 (FMVSS 101) should be used as a guide for CWS and ACC system indicators. 

R4-1 CWS should utilize different audible tones (e.g., different pitches, patterns, 

lengths, etc.) or tactile warnings to provide multiple warnings as an object 

crosses the warning thresholds. 

R4-2 CWS and ACC systems should include a visual indicator when no vehicles or 

objects are in the lane. The indication may be provided by an instrument 

panel warning light or an indicator that is integral to each system. 

R4-3 CWS and ACC systems should use a visual indicator to provide system 

operational status. This status may be indicated by an instrument panel 

warning light or an indicator that is integral to each system.

R4-4 CWS and ACC systems should use a visual or audible indicator to indicate a 

system failure or malfunction. This status may be indicated by an instrument 

panel warning light or an indicator that is integral to the system.

R4-5 CWS and ACC system indicators should be clearly discernable in direct 

sunlight and at night. 

T4-1 OPTIONAL – CWS should utilize combinations of audible, visual and tactile 

indicators to provide multiple warnings of object detection and impending 

collision. 

T4-2 OPTIONAL – CWS may allow the volume of the audible warnings to be 

adjusted, but not below a minimum sound level of 65 dBA7

.

T4-3 OPTIONAL – CWS and ACC systems may provide operational or diagnostic 

messages or codes, such as “System Operational” on an alphanumeric 

display to alert the driver of specific faults, conditions, or concerns. 

3.5 Maintenance and Support Requirements 

Maintenance and support requirements include functionality/features that should be provided to 

ensure CWS and ACC systems will be operated correctly and properly maintained. 

R5-1 CWS and ACC systems should be serviced periodically in accordance with 

system maintenance instructions to maintain system functionality. This 

process maintains the proper alignment and calibration of integral CWS and 

ACC system components, such as the radar sensor, camera, and antennae.

R5-2 Users should be provided with a manual and training for CWS and ACC 

systems. 

R5-3 At a minimum, the user’s manual should include information on the minimum 

vehicle speed at which CWS and ACC systems operate, the conditions under 

which the systems can/cannot detect and track vehicles, and the types of 

indicators used to inform the driver if the systems are functioning properly. 

 

7 For reference: 90 dBA = heavy truck at 10m, 80 dBA = curbside of busy street, 70 dBA = car interior, 60 

dBA = normal conversation at 1m (3.28 ft.), and 50 dBA = office noise. 
14 

R5-4 Manufacturers should provide product support for users and fleets to ask 

questions regarding capabilities and resolve problems with systems. 

T5-1 OPTIONAL – Video, audio, or computer-based training material may be 

provided for fleet management and/or drivers. 

T5-2 OPTIONAL – CWS and ACC systems may be transferable from one vehicle 

to another. System recalibration and/or resetting of system parameters 

should be performed when the system(s) are moved between vehicles.
15 

4. ACRONYMS 

Acronym Definition 

ACC Adaptive Cruise Control 

ASCII American Standard Code for Information Exchange 

COTS Commercial Off-The-Shelf 

CWS (Forward) Collision Warning System(s) 

DVI Driver-Vehicle Interface 

ECU Electronic Control Unit 

EV Eaton VORAD 

FMCSA Federal Motor Carrier Safety Administration 

FMVSS Federal Motor Vehicle Safety Standard 

GES General Estimates System 

GVWR Gross Vehicle Weight Rating 

kph Kilometers per Hour 

mph Miles per Hour 

NHTSA National Highway Traffic Safety Administration 

OBD On-Board Diagnostic 

OEM Original Equipment Manufacturer 

ROI Return on Investment 

SAE Society of Automotive Engineers 

TIFA Trucks Involved in Fatal Accidents 

TMC Technology and Maintenance Council 

USB Universal Serial Bus 

USDOT United States Department of Transportation 

VDC Volts Direct Current 
16 

5. REFERENCES 

Craft, Ralph. FMCSA Paper Rear-End Large Truck Crashes. http:/www.fmcsa.dot.gov/factsresearch/briefs/rear.pdf, 2002. 

SAE Standard J1113, “Electromagnetic Compatibility Measurement Procedures and Limits 

for Vehicle Components (Except Aircraft) (60 Hz to 18 GHz),” July 1995. 

SAE Standard J1455, “Joint SAE/TMC Recommended Environmental Practices for 

Electronic Equipment Design (Heavy-Duty Trucks),” August 1994. 

SAE Standard J1587, “Electronic Data Interchange between Microcomputer Systems in 

Heavy-Duty Vehicle Applications,” February 2002. 

SAE Standard J1708, “Serial Data Communications between Microcomputer Systems,” 

October 1993. 

SAE Standard J1939-71, “Recommended Practice for Control and Communications Network 

for On-Highway Equipment – Vehicle Application Layer,” September 2002. 

Wang, J.S.; Knipling, R.R.; and Blincoe, L.J. The dimensions of motor vehicle crash risk. 

Journal of Transportation and Statistics. Volume 2, No. 1, pp. 19-43, ISSN 1094-8848, 

May 1999. 

Wierwille, W.W.; Lewin, M.G.; and Fairbanks, R.J. III. Final Report: Research on VehicleBased Driver Status/Performance Monitoring; Part I. Vehicle Analysis and Simulation 

Laboratory, Virginia Polytechnic Institute and State University, Publication No. DOT 

HS 808 638, September 1996. 

Wierwille, W.W.; Lewin, M.G.; and Fairbanks, R.J. III. Final Report: Research on VehicleBased Driver Status/Performance Monitoring; Part II. Vehicle Analysis and Simulation 

Laboratory, Virginia Polytechnic Institute and State University, Publication No. DOT 

HS 808 638, September 1996. 

Wierwille, W.W.; Lewin, M.G.; and Fairbanks, R.J. III. Final Report: Research on VehicleBased Driver Status/Performance Monitoring; Part III. Vehicle Analysis and Simulation 

Laboratory, Virginia Polytechnic Institute and State University, Publication No. DOT 

HS 808 638, September 1996. 
17 

A. APPENDIX A – COMMERCIAL-OFF-THE-SHELF CWS AND ACC SYSTEMS 

The following Commercial-Off-the-Shelf (COTS) CWS are currently available:

Delphi Electronics and Safety (www.delphi.com) – Delphi is developing CWS for 

commercial vehicles. The CWS uses a radar sensor to detect slower moving vehicles inlane at a range of up to 80 meters on straight roads and curves of constant radius greater 

than 500 meters. The system provides a warning in sufficient time to avoid a collision when 

the following interval is a minimum of 2 seconds. The system does not feature side or rearobject detection or an interface to an ACC system. 

Eaton VORAD (EV) (www.roadranger.com/VORAD) – The EV EVT-300 CWS is part of a 

larger system including ACC, side object detection, and trip/accident reconstruction data 

recording. The EV CWS uses a front bumper mounted radar sensor and an in-vehicle 

processor to detect and provide warnings of vehicles within the same lane up to 150 meters 

(500 feet) ahead. To permit detection around curves, a yaw gyro provides road curvature 

estimates. A driver display unit, which contains the audible and visual warning devices, 

enables driver adjustment of some of the system’s operating characteristics. 

Mobileye (www.mobileye.com) – The “Mobileye Advanced Warning System” is a camerabased system that includes a small camera and a processing unit mounted to the upper 

center of the windshield and a cell phone-sized alphanumeric/graphic driver display on the 

dashboard. Two in-cab speakers, one on either side of the vehicle, provide audible 

warnings with adjustable volume control. When lane markings are not visible due to dense 

fog, heavy rain or snow, roads covered with mud, ice, or snow; the systems notify the driver 

and shut down. This system is available as a stand-alone system or as an additional feature 

in a more extensive system including lane departure warning, headway indication and 

warning, and cut-in warning and lane change assist features. 

 The following COTS ACC systems will be available currently or in the near future: 

Delphi Electronics and Safety (www.delphi.com) – Delphi is developing ACC systems for 

commercial vehicles. The radar-based systems detect vehicles in-lane at a range of up to 

80 meters on straight roads and curves of constant radius greater than 500 meters. 

Eaton VORAD (EV) (www.roadranger.com/VORAD) – The EV “SmartCruise” ACC system 

is an optional part of a larger system including CWS, side object detection, and trip/accident 

reconstruction data recording. The EV ACC system uses radar to detect vehicles up to 500 

feet ahead. To permit detection around curves, a yaw gyro provides road curvature 

estimates. A driver display unit enables driver adjustment of the system’s operating 

characteristics. 

Mobileye (www.mobileye.com) – The “Mobileye Advanced Warning System” includes a 

small camera and a processing unit mounted to the windshield behind the rear-view mirror 

and a cell phone-sized alphanumeric/graphic driver display on the dashboard. The system 

detects and tracks vehicles ahead of the host vehicle, monitors the distance and following 

time interval to them, and issues commands to the vehicle’s cruise control system to 

maintain a safe following interval. The following interval is adjustable. It is available as a 

stand-alone system or as an additional feature in a more extensive system including lane 

departure warning, forward collision warning, headway indication and warning, cut-in 

warning, and lane change assist features. 
18 

Summary of CWS COTS System Features 

Table A-1 provides comparative information relative to the features of each of the COTS 

systems described in this appendix. Each manufacturer provided this information. 

Table A-1 

Summary of COTS CWS Features 

Feature Delphi EatonVORAD Mobileye 

Detects obstacles, moving and fixed Yes Yes Yes 

Operates on straight and curved roads Yes Yes Yes 

Detects closing rate and alerts driver above a threshold Yes Yes Yes 

Tracks multiple vehicles and objects Yes Yes Yes 

Uses audible and visual collision warnings * Yes Yes 

Uses progressive alert levels No Yes Yes 

Permits adjustment of warning threshold location * Yes Yes 

Permits adjustment of audible warning volume * Yes Yes 

Permits temporary disabling of detection * Yes No 

Has visual tracking indicator * Yes Yes 

Has visual system status indicator * Yes Yes 

Has audible or visual system failure indicator * Yes Yes 

Provides a Driver Interface Unit * Yes Yes 

Has a proximity alert * Yes No 

Interfaces to ACC System * Yes Yes 

Logs data internally No Yes Yes 

Data messages available * Yes No 

Data link used * J-1587/ 

J-1939 

Ethernet or 

USB 2.0 

Aftermarket installation by fleets possible * Yes Yes 

* As of release of this document, details for this feature have not been determined. 
19 

Summary of ACC System COTS System Features 

Table A-2 provides comparative information relative to the features of each of the COTS 

systems described in this appendix. Each manufacturer provided this information. 

Table A-2 

Summary of COTS ACC System Features 

Feature Delphi EatonVORAD 

Mobileye 

Operates on straight and curved roads Yes Yes Yes 

Tracks multiple objects Yes Yes Yes 

Provides a Driver Interface Unit * Yes Yes 

Has system status indicator * Yes Yes 

Displays range and following interval to vehicle ahead * No Yes 

Permits adjustment of following interval * Yes Yes 

Interfaces to CWS * Yes Yes 

Logs data internally No Yes No 

Data messages available * Yes Yes 

Data link used * J-1587/ 

J-1939 

Ethernet or 

USB 2.0 

Aftermarket installation by fleets possible * Yes Yes 

*As of release of this document, details for this feature have not been determined. 
Report No. FMCSA-MCRR-05-007 

For more information on the Federal 

Motor Carrier Safety Administration and 

the Office of Research and Analysis, 

check out our website at www.fmcsa.dot.gov