Exploratory Advanced Research . . . Next Generation Transportation Solutions

Cooperative Adaptive Cruise Control

Taking Cruise Control to the Next Level

Advancing the State-of-the-Art

The sensor-based adaptive cruise control (ACC) 

currently in use has significant performance limitations. These include a long delay in responding to 

motion changes by the preceding vehicle and a 

minimum time gap of 1 second in following the 

preceding vehicle, which is long enough to encourage other vehicles to cut into the traffic stream. 

This EAR project will enable CACC to overcome 

these limitations and provide significantly better 

performance for drivers. CACC enables vehicles 

to follow each other more closely and accurately 

than does conventional ACC, thus improving 

traffic flow and allowing drivers to safely use 

their cruise control at shorter gap settings. These 

shorter gaps can make it possible to almost 

double the capacity of a highway lane. CACC 

also helps drivers to feel more confident using 

cruise control, as the system activates braking 

action faster than a driver can react to brake 

lights on the preceding vehicle. 

Researchers will also fill the gaps in knowledge and performance that need to be bridged 

before field operational tests of CACC can 

begin, which will be needed to enable commercialization of the technology. Knowledge gaps 

include defining the maneuvers that vehicles 

have to perform to join and leave a CACC 

“platoon” or stream of vehicles under different 

conditions and demonstrating how vehicle-tovehicle message sets can be adjusted to support 

CACC operations. These sets allow vehicles to 

send wireless messages to other vehicles about 

such data as speed, location, and application 

of brakes.

Developing Simulation Models

The project researchers began their work by 

identifying operational concept alternatives to 

study in greater depth, such as multiple strategies for operating CACC platoons. The research 

team next developed simulation models to 

The Exploratory Advanced Research Program Fact Sheet

Using a combination of sensors and 

vehicle-to-vehicle communication, 

cooperative adaptive cruise control 

(CACC) takes cruise control to the next 

level, enabling vehicles to adjust their 

speed to the preceding vehicle in their 

lane. The CACC system can also respond 

more quickly to speed changes by the 

preceding vehicle and other vehicles 

farther ahead that are beyond the line 

of sight. These advancements improve 

the stability of traffic flow, increase 

driver confidence, and make shorter 

vehicle-following distances possible. 

Ultimately this results in better use of 

a highway’s effective capacity and 

greater fuel efficiency. 

Overcoming the key remaining 

technical challenges to implementing 

CACC is the goal of the Exploratory 

Advanced Research (EAR) Program 

project “Using Cooperative ACC to Form 

High-Performance Vehicle Streams.” 

The California Partners for Advanced 

Transportation Technology (PATH) 

Program at the University of California, 

Berkeley (UC Berkeley), is conducting 

this research, which is funded by the 

Federal Highway Administration (FHWA). 

The Technical University of Delft in the 

Netherlands is PATH’s research partner. 
represent diverse real-world conditions, including 

urban versus rural roads, highways versus arterial 

roads with traffic signals, and different levels of 

traffic volume. Traffic simulation models also 

included a new program developed in the 

Netherlands, MOTUS (Microscopic Open Traffic), 

and the commercially available Aimsun model 

used by the PATH Program. The researchers then 

used the simulation models to assess the traffic 

flow and energy impacts of the various operational concepts under different deployment 

scenarios. They divided the simulation model 

work among the teams at UC Berkeley and the 

University of Delft so that each team could validate the work of the other. Metrics assessed by 

the models included increases achieved in traffic 

flow capacity per highway lane, reductions in 

traffic flow disturbances, reductions in vehicle 

energy consumption, and savings in travel times 

along arterial roadways.

Analyzing the Data

The researchers have been analyzing the results 

of the simulation studies and using the data 

to identify the next generation of vehicle experiments that should be conducted to verify the 

feasibility of the most promising CACC strategies. They also have been analyzing data that 

PATH previously collected in tests of two generations of experimental CACC systems. This 

analysis is helping to expand understanding 

of how drivers choose to use both ACC and 

CACC and to clarify the safety implications of 

the shorter gaps in the vehicle stream enabled 

by CACC. 

Next Steps

The project researchers will next test their simulation models at FHWA’s Saxton Transportation 

Operations Laboratory in McLean, VA. 

What Is the Exploratory 

Advanced Research Program?

FHWA’s Exploratory Advanced Research 

(EAR) Program focuses on longer term, 

higher risk research with a high payoff 

potential. The program addresses underlying gaps faced by applied highway 

research programs, anticipates emerging 

issues with national implications, and 

reflects broad transportation industry 

goals and objectives. To learn more about 

the EAR Program, visit the EAR Web site 

at www.fhwa.dot.gov/advancedresearch. 

The site features information on research 

solicitations, updates on ongoing research, 

links to published materials, summaries of 

past EAR Program events, and details on 

upcoming events. 

Cooperative Adaptive Cruise Control

Taking Cruise Control to the Next Level

Publication No. 

FHWA-HRT-16-044

HRTM-30/02-16(WEB)E 

Importance to FHWA

The project researchers are making important 

advances in overcoming the technical challenges 

that currently stand in the way of implementing 

CACC. These project results will accelerate progress toward testing and evaluation of CACC on 

the road, which is the next step in moving the 

technology closer to real-world deployment. 

Learn More

For more information about the EAR project 

“Using Cooperative ACC to Form HighPerformance Vehicle Streams,” contact Bob Ferlis 

in the FHWA Office of Operations Research 

and Development, 202-493-3268 (email: robert.

ferlis@dot.gov). 

Photo credit, page 1: 

© Leidos 

FHWA test vehicles simulate 

a “platoon” or stream of 

vehicles using cooperative 

adaptive cruise control, 

which improves traffic flow 

and allows drivers to use 

their cruise control at 

shorter gap settings.