Office of Safety and Operations 

Research and Development 

1

Move Over Law for Traffic Incident Management Using 

Cooperative Driving Automation (CDA)

The intent of a move over law(1) feature aims to protect first 

responders as they respond to an incident. When first responders 

are positioned near or in active travel lanes, they and their 

vehicles may be put in harm’s way due to the close proximity of 

other vehicles. All 50 States have some form of a move over law, 

whereby approaching users are required to slow down and move 

over to ensure the safety of first responders. This CDA feature 

allows emergency response vehicles (ERVs) to broadcast a 

vehicle-to-everything (V2X) message containing the Global 

Positioning System point of the incident, along with a desired 

speed reduction and desired safety margins for the passing 

vehicles. Surrounding vehicles would receive and interpret this 

information to avoid the lane (or space, as shown in figure 1) 

adjacent to the ERV and reduce their speed when passing.

BENEFITS TO TRANSPORTATION

© Getty Images Plus.

Figure 1. Image. Developed feature demonstration 

at Turner-Fairbank Highway Research Center.

Source: Federal Highway Administration.

Cooperative automated driving system-equipped vehicles can safely navigate the traffic incident 

location, reduce the likelihood of a crash, and improve emergency responder safety by providing 

connected ERVs with the capability to broadcast traveler information messages. These messages 

describe restricted travel paths and require vehicles to either slow down or move over.

By notifying vehicles and drivers of an upcoming road rule change due to the presence of an 

incident, CDA-enabled vehicles can proactively adjust to closed lanes, slow down, and make 

other possible changes to support a continued smooth traffic flow at the incident site.

IMPROVED FIRST-RESPONDER SAFETY

IMPROVED MOBILITY

USE CASE ARCHITECTURE

CARMA PlatformSM(2) and CARMA MessengerSM(3) operate in 

tandem to enable CDA technology to work. CARMA 

Messenger broadcasts the V2X message to any vehicles 

within communication range, and CARMA Platform 

interprets the message and controls the vehicle to operate 

within the parameters set in the broadcasted message.

STANDARDS

This technology uses the following standards established 

by SAE International®:

 SAE® J3216_202107TM: Taxonomy and Definitions for 

Terms Related to CDA for On-Road Motor Vehicles.

(4)

 SAE® J3016_202104TM: Taxonomy and Definitions for 

Terms Related to Driving Automation Systems for 

On-Road Motor Vehicles.(5)
TITLE OF TECHBRIEF

2

Collaborate with industry 

partners and emergency 

responders to determine 

best practices pertaining to the 

messaging of traffic incident-related 

information and use this information 

to propose new standardized 

messages.

Develop more robust 

software. Build out software 

to be more robust for a larger 

set of situations and have fewer 

software bugs.

Conduct more testing, since 

only one use case was tested. 

Further testing can involve a 

larger set of situations, more 

simulation testing, and more 

complicated incidents for vehicles 

to respond to.

EVALUATION OF THE CONCEPT 

Independent evaluators from the U.S. Department of Transportation Volpe National Transportation Systems Center 

tested this system, in the planned scenario, using the following criteria:

1. The pulled-over ERV can broadcast messages using CARMA Messenger(3) that describe its current location and the 

length of the road affected by the incident.

2. A CDA vehicle using CARMA Platform(2) can receive the messages from the ERV and appropriately modify its route 

by changing lanes away from the lane immediately adjacent to the ERV and also reduce its speed when passing 

through the affected region.

3. The CDA vehicle using CARMA Platform changes back to its original lane and increases its speed to the normal 

speed limit after exiting the incident.

4. The CDA vehicle smoothly and correctly follows both the normal speed limit as well as a reduced speed 

throughout the use case.

CARMA Platform and CARMA Messenger operate in tandem to enable this technology to work. CARMA Messenger 

broadcasts the V2X message to any vehicles within communication range. CARMA Platform interprets the message 

and controls the vehicle to operate within the parameters set in the broadcasted message and exit the location 

transmitted by the ERV.

RESULTS AND LESSONS LEARNED

While the system met the criteria for item 1 and item 2 in the Evaluation of the Concept section, the Volpe Center 

recommended that the CARMA Platform(2) system used by the CDA vehicle be tuned for smoother vehicle acceleration 

and deceleration when both approaching and exiting the location transmitted by the ERV.

CONCLUSIONS

Move over laws(1) proved that documented benefits could be achieved through the application of CDA traffic incident 

management scenarios and helped provide a better understanding of its advantages. Through data collection and 

analysis, the research team outlined some suggested improvements, and potential for future work remains. The next 

steps for the feature are as follows:

MOVE OVER LAW FOR TRAFFIC INCIDENT MANAGEMENT USING CDA

TO LEARN MORE AND FOLLOW UPDATES:

CARMA Platform

https://github.com/usdotfhwa-stol/carma-platform

CARMA Messenger

https://github.com/usdotfhwa-stol/carma-messenger

For more information, please contact the CDA Program at CDA@dot.gov

FHWA-HRT-24-027

HRSO-40/12-23(200)E

Recommended citation: Federal Highway Administration. Move Over Law for Traffic Incident 

Management Using Cooperative Driving Automation (CDA) (Washington, DC: 2023) 

https://doi.org/10.21949/1521467

1 USDOT. n.d. “Move Over: It’s the Law” (web page). https://www.nhtsa.gov/move-over-its-law, last accessed November 21, 2023.

2 FHWA. n.d. “carma-platform” (software and configuration files in GitHub repository). https://github.com/usdot-fhwa-stol/carma-platform, last accessed April 12, 2023.

3 FHWA. 2023. CARMA Messenger (software). Version 4.4.0.

4 SAE International. 2020. Taxonomy and Definitions for Terms Related to Cooperative Driving Automation for On-Road Motor Vehicles. SAE J3216_202107. Warrendale, PA: SAE International. 

https://www.sae.org/standards/content/j3216_202107/, last accessed July 16, 2021.

5 SAE International. 2018. Taxonomy and Definitions for Terms Related to Driving Automation Systems for On-Road Motor Vehicles. SAE J3016_202104. Warrendale, PA: SAE International. 

https://www.sae.org/standards/content/j3016_202104/, last accessed May 30, 2023.