Three deceleration zones, one SPaT message, zero violations.
Red Light Violation Warning uses real-time SPaT and MAP messages broadcast from the intersection RSU to let connected vehicles predict whether they can safely clear the intersection — and if not, brake in a controlled, zoned cascade. A safety-critical application where communications quality is paramount.
The RSU at each signalized intersection pulls SPaT data directly from the traffic signal controller and broadcasts SPaT + MAP messages. Each connected vehicle correlates its position, speed, and the signal state to decide if it's a potential red-light runner, then applies a three-zone deceleration profile.
MAP messages at 1 Hz (intersection geometry). SPaT messages at 10 Hz (current phase, time to next phase). 1,640 ft range covers the intersection comfortably.
Each CV checks: am I too close to the stop bar? Am I traveling too fast? Is there no leader ahead? If yes — and the signal won't permit clearance — it's flagged as a potential runner.
L_th1 is fixed at 32.8 ft. L_th2 = 3× the vehicle's braking distance at current speed (normal deceleration). L_th3 = 5× the same braking distance. These bound three deceleration zones.
Zone 3 (between L_th2 and L_th3): decelerate at d_normal. Zone 2 (between L_th1 and L_th2): decelerate at 2× d_normal. Zone 1 (inside L_th1): emergency brake at 4× d_normal. The algorithm doesn't fire beyond L_th3.
Longer-cycle signalized intersection with through, left, and right movements. RSU at the intersection, stop-bar and advance detectors at each approach for actuated control.
Same speed, shorter cycle — tests algorithm performance under more frequent phase transitions where SPaT timing uncertainty matters more.
Lower-speed arterial, short cycle. Smaller braking distance multiples produce tighter deceleration zones.
Under ideal communications the algorithm prevents red-light running across all speeds and cycle lengths. Latency degrades it; packet loss less so; and CV penetration acts as a stabilizer.
At zero latency and zero packet loss, the three-zone braking strategy prevents red-light violations across all three test networks. The control logic itself is sound.
As latency or packet loss rises, the algorithm's effectiveness drops — most sharply when CV penetration is low. Few CVs + degraded comms = many missed brakes.
Even at zero latency, the algorithm performs reasonably well across packet-loss rates. Add latency and the failures compound much faster. Communications jitter is the bigger enemy than message drops.
At 90% and 100% penetration, the negative effects of latency and packet loss become much smaller. More CVs in the network smooths out individual missed messages.
At 1,640 ft the RSU covers the entire intersection comfortably, so range was not swept. For larger or non-standard intersections this would need re-evaluation.
Followed Aimsun Technical Support guidance: define a compliant-vehicle signal group, then introduce non-compliant 'through' vehicles that ignore traffic signals. 100% of through vehicles are modeled as potential runners — an extreme scenario.
Red Light Violation Warning is a clear win for V2X — the algorithm works, but only if the agency invests in the communications layer that carries it.
The simulation makes the case that real-time SPaT and MAP information can prevent red-light running through pre-emptive, zoned deceleration. The control logic is robust enough that latency and packet-loss sensitivity reveal themselves only in degraded-communications regimes — meaning the algorithm is not the weak link.
The latency-versus-packet-loss asymmetry is operationally significant. Network jitter is much harder to engineer out than message reliability, and it's the dominant degradation factor. Agencies sizing V2X infrastructure should prioritize low-latency message paths over high-redundancy packet delivery.
The stabilizing effect of high CV penetration is the strongest argument for an aggressive deployment runway. Caltrans's value proposition isn't 'install RSUs and hope' — it's 'partner with the private sector to drive CV adoption, because the technology pays off in proportion to how many vehicles can use it.'
Specify low-latency communications hardware and network design for any Red Light Violation Warning deployment. Latency degrades performance faster than packet loss does.
Pair RSU installation with a parallel push for CV adoption — high penetration stabilizes the algorithm against communications imperfection.
Use the three-zone deceleration profile as the algorithmic baseline: L_th1 = 32.8 ft, L_th2 = 3× braking distance, L_th3 = 5× braking distance with 4× / 2× / 1× normal deceleration in zones 1 / 2 / 3.
Broadcast SPaT at 10 Hz and MAP at 1 Hz at minimum. SPaT freshness directly determines algorithm precision.
Coordinate with private-sector OEMs and connected-vehicle vendors. Public deployment alone won't reach the penetration rates that make the system robust.