Free C-V2X message decoder, creator and RSU portal
Paste a packet from an RSU, OBU or capture and read it in plain English. Build a SPaT, MAP, TIM, work-zone RSM or SDSM from a validated template, then push it to your own roadside unit. Built on the current standards, run on ITS Roads servers, free to use.
Decode a message without leaving this page
Paste hex, base64, XER or JSON. Or load one of the samples. The work runs on ITS Roads servers at cv2x.itsroads.com; nothing to install.
Free use is a few decodes a day per visitor. A free account raises that to 500 a day and unlocks the RSU registry and message push.
Every message in the 2024 dictionary, every layer of the packet
Decode anything
Raw UPER MessageFrame, IEEE 1609.2 signed or unsigned PDUs, IEEE 1609.3 WSMP frames and whole Ethernet captures. The tool peels each layer, reports the PSID and signer, and decodes the J2735 payload into JSON, XER and a readable summary.
Create and validate
Start from a validated template (BSM, SPaT, MAP, TIM advisory, TIM speed limit, RSM work zone, PSM, SRM, SSM, SDSM, EVA, RTCM), edit the fields that matter, and encode. Every range, size and enumeration is checked against the standard before you get bytes.
See it on a map
MAP lanes, TIM regions, RSM reference paths, BSM path history and SDSM detected objects are drawn on a map so you can check geometry by eye, not by arithmetic.
Push to your RSU
Register a roadside unit with its SNMPv3 credentials and push a store-and-repeat or immediate-forward message over NTCIP 1218, the same objects a traffic management center uses, on NTCIP 1218 v01A as CTI 4001 requires.
Current standards, backward and forward compatible
Encodes on SAE J2735_202409 with the J2945/4 Road Safety Message and J3224 Sensor Data Sharing Message, and decodes captures from 2016 and 2020 devices automatically. IEEE 1609.2 and 1609.3, NTCIP 1218 v01A, CTI 4001, FCC 24-123. When the 2026 revision publishes we add it alongside.
A question mark beside every field
Each field in a decoded or drafted message has a ? that explains what it means, its units and range, the unavailable value, and where the number comes from in practice. A structure explorer lets you add optional parts by clicking instead of typing JSON.
Draw MAP and TIM messages on a map
Place the reference point, draw lanes and crosswalks, link ingress to egress with signal groups, and get a valid MAP. Draw TIM and RSM work-zone regions, or a whole corridor split into a batch of messages, then export UPER hex, JSON, XER or GeoJSON, or push the set to your RSUs.
Live traffic from your RSU
Forward received messages from an RSU to the portal over NTCIP 1218 and watch vehicles, breadcrumb trails, MAP lanes colored by the live SPaT, and SRM/SSM signal-priority requests. Record, replay, export, and set geofence, speed, hard-braking and priority triggers with alerts. A demo corridor runs around the clock.
A wiki for agencies and researchers
Every message explained field by field, how signal timing works, how MAP binds to SPaT, how buses, snow plows, freight and EMS get signal priority, SCMS, FCC licensing, NTCIP 1218 and TMC integration, and a research and pilot playbook.
Guides that answer the hard questions
How to get SCMS enrollment and application certificates, how to bootstrap an RSU, how to license C-V2X radios with the FCC, what OmniAir certification covers, and where the state DOT and university deployment resources are.
Register your RSU, free. Hand it to us when you want it managed.
The portal keeps each account's devices separate, encrypts credentials at rest, logs every push and never broadcasts anything you did not ask for. Use it to test a new intersection, verify a vendor's message, or keep a work-zone TIM current without opening the vendor console.
Free
- Decode and create messages, 500 a day with an account
- Register up to 25 RSUs with coarse locations on the public map if you choose
- Push messages over NTCIP 1218, with a push log you can audit
- Connection test and SNMP troubleshooting output
- Standards references, SCMS and FCC licensing guides
Managed by ITS Roads
- Dedicated portal and monitoring for your fleet
- SCMS enrollment, certificate renewals and misbehavior reporting handled for you
- SPaT, MAP, TIM and RSM generation and maintenance from your signal timing and work-zone data
- Firmware, NTCIP 1218 conformance, OmniAir readiness and FCC licensing support
- 24/7 monitoring with your existing enterprise platforms
SAE J2735_202409 message IDs and PSIDs
| Message | messageId | PSID (IEEE 1609.12) | Typical source |
|---|---|---|---|
| MAP, intersection geometry | 18 | 0xE0000017 (legacy 0x8002) | RSU store-and-repeat |
| SPaT, signal phase and timing | 19 | 0x8002 | Signal controller via RSU, 10 Hz |
| BSM, basic safety message | 20 | 0x20 | Vehicles, 10 Hz |
| SRM / SSM, signal request and status | 29 / 30 | 0xE0000016 / 0xE0000015 | Transit and emergency vehicles / controller |
| TIM, traveler information | 31 | 0x8003 | TMC via RSU |
| PSM, personal safety message | 32 | 0x27 | Pedestrians, cyclists, work crews |
| RSM, road safety message (work zones) | 33 | agency assigned | TMC and work-zone systems |
| SDSM, sensor data sharing | 41 | 0x8010 | RSU-attached sensors |
| RTCM corrections | 28 | 0x8000 | RSU |
The 2024 dictionary defines 33 operational messages (IDs 18 to 50) plus 16 test messages. The portal decodes all of them and the 1,218 underlying types.
Built from the reference codec, tested end to end
The decoder is compiled from the USDOT Joint Program Office's generated J2735_202409 codec source, the same lineage the Operational Data Environment uses, with an ITS Roads JSON layer that round-trips every one of the 1,218 types byte for byte. Every create runs the full constraint check before it hands you bytes. We use the same engine in our RSU monitoring work for state DOT fleets of Commsignia and Yunex units, where the message store, security subsystem and NTCIP 1218 objects are read over SNMP from hundreds of roadside units.
Is the J2735 decoder really free?
Yes. Anyone can decode or create a few messages a day without an account. A free account raises the limit to 500 a day, lets you register RSUs, and push messages to them. Processing runs on ITS Roads servers, nothing is installed on your side.
Which J2735 revision does it use?
SAE J2735_202409, the current published revision, including the J2945/4 Road Safety Message (work zones) and J3224 Sensor Data Sharing Message modules that ride the same MessageFrame. When SAE publishes the next revision we will add it alongside, so older captures keep decoding.
What inputs can I paste?
Raw UPER MessageFrame hex, base64, XER, JSON, an IEEE 1609.2 secured PDU (signed or unsigned), an IEEE 1609.3 WSMP frame, or a whole Ethernet frame with EtherType 0x88DC. The tool peels each layer and tells you what it found, including the PSID and the signer.
How does the RSU push work?
You register the RSU with its address and SNMPv3 authPriv credentials. The portal validates your message, then writes a row to the NTCIP 1218 store-and-repeat or immediate-forward table over SNMP, exactly as a traffic management center would. The RSU signs the message with its own SCMS certificate. Credentials are encrypted at rest and each account is isolated.
Can ITS Roads manage our RSUs for us?
Yes. Registration and the tools are free. If you want ITS Roads to own the work, SCMS enrollment, message generation, monitoring, firmware and FCC licensing support, we scope a dedicated managed service under contract.
- SAE J2735_202409, V2X Communications Message Set Dictionary
- SAE J2945/4_202305, Road Safety Message (work zones)
- SAE J3224_202208, Sensor Data Sharing Message
- IEEE 1609.2, security services for V2X
- IEEE 1609.3, networking services (WSMP)
- NTCIP 1218 v01, Object Definitions for Roadside Units
- CTI 4001 v01, Roadside Unit standard (ITE, AASHTO, NEMA, SAE)
- FCC 24-123, C-V2X rules for the 5.895 to 5.925 GHz band
- USDOT ITS JPO, National V2X Deployment Plan
- USDOT jpo-ode asn1_codec, generated J2735 codec source
- SCMS Manager, industry security credential management policies
- OmniAir Consortium, certification and plugfests
Ready to scope it?
Send us the corridor, the site count and the problem. We will come back with an approach, not a brochure.