ITS RoadsCV2X

Guides › The standards behind connected-vehicle messages, and which revisions are current

Updated 2026-10-08

Why the revision matters

A connected-vehicle message is only useful if the sender and receiver agree on the same dictionary. SAE J2735 defines that dictionary, and it changes: fields are added, some are deprecated, and a message encoded against one revision can fail to decode, or decode wrongly, against another. Everything in this portal is built on the revision that is current as of October 2026, and this page lists the companions you will meet in a procurement, a test plan or a plugfest.

SAE J2735_202409 (September 2024)

The V2X Communications Message Set Dictionary. It defines the MessageFrame wrapper, the message IDs, and every data element: BasicSafetyMessage (BSM, ID 20), SPAT (19), MapData (18), TravelerInformation (TIM, 31), PersonalSafetyMessage (PSM, 32), SignalRequestMessage and SignalStatusMessage (SRM 29, SSM 30), RTCMcorrections (28), EmergencyVehicleAlert (22), ProbeVehicleData (26) and the newer messages up to ID 50. Two companions now ship inside the same package and ride the same MessageFrame:

  • SAE J2945/4 Road Safety Message (RSM, ID 33) for work zones, reduced speed zones and lane closures.
  • SAE J3224 Sensor Data Sharing Message (SDSM, ID 41) for infrastructure and vehicle sensors sharing detected objects.

No revision newer than J2735_202409 has been published. SAE is drafting a 2026 revision. The portal is built for both directions: it carries codecs for the 2016 (J2735_201603), 2020 (J2735_202007) and 2024 revisions, auto-detects which one a capture was encoded with (newest first, falling back when the current dictionary does not consume the whole message), encodes new messages on 2024, and will add the 2026 set beside them the day USDOT publishes its generated code, so today's captures and templates keep working.

The ASN.1 module is distributed by SAE (the J2735, J2735ASN and J2735SET products are now free downloads with an SAE account) and may not be redistributed. This portal uses the USDOT Joint Program Office's generated codec source (Apache-2.0) and credits SAE as the owner of the message set. Get the standard at sae.org.

Companion SAE standards

StandardWhat it coversCurrent revision
J2945/1BSM minimum performance requirements (on-board)J2945/1_2026 (listed October 2026; supersedes 202004)
J2945/BSignal priority and preemption (SRM/SSM applications)J2945/B_202511
J2945/4Road Safety Message (work zones)J2945/4_202305
J2945/ARoadside unit application requirements (RGA)J2945/A_202410
J2945/CProbe dataJ2945/C_202206
J3224Sensor Data Sharing MessageJ3224_202208
J3161/1LTE-V2X (C-V2X PC5) deployment profileJ3161/1_202509
J2540/2ITIS phrase codes used in TIM contentJ2540/2_202012

IEEE 1609 family

  • IEEE 1609.2 security services: the Secured Protocol Data Unit (SPDU) that carries every broadcast message with its signature, certificate or certificate digest, PSID and generation time. The 2025 revision was published in October 2026; 1609.2.1 covers certificate management with the SCMS. The decoder unwraps signed and unsigned SPDUs and reports the signer, hash, PSID and generation time.
  • IEEE 1609.3 networking services: the WSMP header (version, TPID, PSID, length) in front of the SPDU. Current: 1609.3-2020 with Corrigendum 1-2024.
  • IEEE 1609.12 identifier allocations: the PSIDs. Written the way NTCIP tables and tools carry them (p-encoded octets): BSM 20, PSM 27, RTCM 8000, SPaT 8002, TIM and RSM 8003, MAP E0000017 (legacy 8002), SSM E0000015, SRM E0000016, SDSM 8010. The registered integer values differ (8002 is PSID 0x82, 8003 is 0x83); the decoder shows both.

Roadside unit standards

  • NTCIP 1218 v01A (Amendment A, June 2024) Object Definitions for Roadside Units: the SNMP objects an agency uses to configure and monitor an RSU, including the store-and-repeat and immediate-forward message tables this portal writes to. See the NTCIP 1218 push guide.
  • CTI 4001 v01 Roadside Unit standard (ITE, AASHTO, NEMA with SAE): the procurement-ready RSU specification that replaced the USDOT RSU Specification 4.1. It requires C-V2X PC5, IEEE 1609.2 security with SCMS, NTCIP 1218 management, and defines how the RSU forwards received messages to the back office.
  • CTI 4501 v01 Connected Intersections implementation guide: how SPaT and MAP must be generated and verified so every vehicle interprets an intersection the same way.
  • USDOT RSU Specification 4.1 (2016): superseded by CTI 4001. Devices still on it are DSRC-era hardware that must be replaced before the December 14, 2026 sunset; the portal does not target its MIB.

Spectrum and licensing

FCC 24-123 (Report and Order, November 2024) set the final rules for C-V2X in the upper 30 MHz of the 5.9 GHz band (5.895 to 5.925 GHz), with the rules effective February 2025 and the DSRC sunset on 14 December 2026. Roadside units need an FCC license; vehicles operate under a blanket authorization. See the FCC licensing guide.

Where to look things up