Intelligent Traffic Signal Control: How Can Cellular Modem Ensure Millisecond-Level Command Response and Zero Packet Loss?
At a crossroads in Nanshan District, Shenzhen, the morning rush hour sees a torrent of traffic. As the green light is about to switch to red, an ambulance sirens its way forward. At this moment, the traffic signal control system must complete the following actions within 50 milliseconds: identify the ambulance's location, calculate the optimal passage route, and send a delayed red light command to the traffic lights at surrounding intersections. If the signal transmission delay exceeds 100 milliseconds, the ambulance may become stuck in the traffic, delaying the critical rescue time. This scenario reveals the core pain point of intelligent transportation: millisecond-level command response and zero packet loss transmission are key to safeguarding the lifeblood of urban transportation.
Traditional traffic signal control relies on wired networks or public Wi-Fi, but factors such as underground pipeline construction and severe weather often lead to line interruptions. Data from the transportation bureau of a first-tier city shows that in 2024, 63% of signal light anomalies caused by network failures were due to wired network interruptions. More critically, the delay of 4G networks during peak hours can exceed 300 milliseconds, far surpassing the 100-millisecond threshold required by traffic systems. This delay results in:
Obstructed passage for emergency vehicles: Special vehicles such as ambulances and fire trucks are unable to obtain priority passage in a timely manner;
Ineffective traffic flow scheduling: Adaptive signal control algorithms make incorrect decisions due to data delays, exacerbating congestion;
Increased accident risk: Errors in calculating the duration of yellow lights may lead to rear-end collisions.
In vehicle-road coordination scenarios, each intelligent connected vehicle needs to send 200 pieces of data per second to roadside units (RSUs), including vehicle speed, position, and steering intentions. If the data packet loss rate exceeds 0.1%, the RSU may misjudge the traffic situation due to missing information. In an autonomous driving test area, a "phantom traffic jam" occurred due to data packet loss: three test vehicles braked sharply in succession after failing to receive the deceleration signal from the vehicle ahead, triggering a chain reaction among the following vehicles.
Traditional cellular modem devices face multiple challenges in traffic scenarios:
Poor environmental adaptability: High-temperature and high-humidity conditions in underground wells cause capacitor bursts, shortening device lifespan by 60%;
Weak anti-interference capability: Electromagnetic pulses generated by subway operations can cause ordinary cellular modem to restart frequently, with an average of 12 daily disconnections;
High maintenance costs: Records from the transportation bureau of a second-tier city show that in 2024, there were 327 network anomalies, of which 85% required on-site troubleshooting. Maintenance personnel walked an average of 25 kilometers per day, covering only 40% of the devices.
Cellular modems, represented by the USR-DR154, build a redundant transmission network through "5G + 4G + LoRa" tri-mode communication:
5G private network: Provides 10ms-level low-latency control command transmission for vehicle-road coordination, supporting real-time adjustment of dynamic routes;
4G backup link: Automatically switches to the 4G network when the 5G signal is interrupted, ensuring continuous basic communication;
LoRa local networking: Transmits critical safety data via LoRa in signal blind spots (such as inside tunnels) to maintain basic operations.
In tests conducted in Suzhou Industrial Park, this solution increased the transmission success rate of traffic light control commands from 88% to 99.98%, with network switching delays below 50 milliseconds. When an ambulance enters a 500-meter radius of an intersection, the system can adjust the traffic lights 3 seconds in advance, buying precious time for the life corridor.
The traffic device ecosystem is in a chaotic state of "seven kingdoms and eight systems": traffic signal controllers use CAN bus protocols, cameras use RTSP protocols, and RSUs rely on ZigBee architectures. The USR-DR154, with built-in standardized communication protocol libraries such as BACnet, Modbus, and CANopen, supports:
Edge computing gateways: Parsing private protocol data from traditional devices into standard protocol data for upload to cloud platforms;
Protocol interconversion: Enabling rapid bidirectional transparent transmission of RS232/RS485 serial data with 4G, Ethernet, and Wi-Fi networks;
VLAN subnet partitioning: Constructing independent subnets through one 100Mbps WAN port and four 100Mbps LAN ports to avoid broadcast storms.
Practice in a smart transportation project shows that this solution successfully integrated over 2,000 devices from 12 brands, achieving real-time data synchronization and centralized display, reducing transformation costs by 70%, and controlling data collection delays within 80 milliseconds.
The USR-DR154 ensures zero packet loss transmission through three mechanisms:
Hardware-level redundancy: Dual SIM card slots support switching between primary and backup carriers, automatically switching to China Unicom or China Telecom when mobile network failures occur;
Software-level retransmission: Built-in TCP/UDP retransmission protocols automatically trigger three retransmissions when data packets are lost;
Caching mechanism: A 16MB local storage space can temporarily store data during network interruptions, prioritizing the transmission of historical data upon recovery.
In real-world tests conducted in Tianhe District, Guangzhou, this solution reduced the data packet loss rate from 2.3% to 0.0001%, meeting the requirement of "key data packet loss rate ≤ 0.1%" in the Ministry of Transport's "Administrative Regulations on Road Testing of Intelligent Connected Vehicles."
During the Hangzhou Asian Games, the emergency vehicle priority system supported by the USR-DR154 achieved:
Real-time identification: Precisely locating ambulances through UWB communication between RSUs and vehicle-mounted OBUs;
Dynamic adjustment: Adjusting traffic light timing 200 meters in advance to reserve dedicated lanes for emergency vehicles;
Global coordination: Extending the impact range to three adjacent intersections to prevent traffic backflow.
Data shows that this system reduced emergency vehicle passage time by 40% and improved rescue response efficiency by 25%.
In the Chunxi Road business district of Chengdu, 200 sensors connected to the USR-DR154 achieve:
All-element perception: Real-time collection of data such as traffic flow, pedestrian density, and queue length;
AI decision-making: Dynamically optimizing traffic light timing plans based on reinforcement learning algorithms;
Millisecond-level response: Adjusting traffic lights at surrounding intersections within 50 milliseconds when sudden accidents are detected.
After the transformation, the morning rush hour congestion index in the area dropped from 2.1 to 1.3, reducing the average vehicle passage time by 18 minutes.
In Zhangjiang Science City, Shanghai, the vehicle-road coordination system supported by the USR-DR154 achieves:
V2X communication: Real-time interaction between vehicles and roadside units through 5G-V2X technology;
Collaborative decision-making: Expanding the perception range of single vehicles from 50 meters to 300 meters, improving decision-making accuracy;
Safety warnings: Sending safety information such as collision warnings and blind spot monitoring to vehicles 3 seconds in advance.
Tests show that this system reduced the traffic accident rate by 60% and improved traffic efficiency by 35%.
With the maturation of 6G networks and digital twin technology, traffic signal control will enter a new stage:
Omni-perception: Building a real-time updated digital twin city in the cloud, achieving precise synchronization between the virtual and physical worlds through the UWB + laser SLAM fusion solution of the USR-DR154;
Vehicle-road-cloud integration: Deep collaboration between vehicles, roads, and the cloud for fully autonomous operations;
Energy Internet: Two-way interaction between traffic lights and the power grid, automatically adjusting electricity consumption strategies based on photovoltaic output forecasts and prioritizing the use of clean energy.
On the track of intelligent transportation, cellular modem are no longer just "digital bridges" connecting devices but have become the "nerve centers" reconstructing the transportation ecosystem. From the life-and-death speed of an ambulance in Shenzhen to the traffic congestion alleviation miracle in Chunxi Road, Chengdu, the USR-DR154 is breaking through industry pain points through technological innovation and reshaping urban value with data intelligence.
For transportation management authorities, it is essential to reserve standardized communication interfaces during the planning stage to avoid technical barriers in later transformations. For device manufacturers, they should actively embrace open protocols to break the monopoly of private systems. For users, it is necessary to establish a data-driven management mindset and fully explore the value-added services after device interconnection. When technology returns to humanity and intelligence serves safety, urban transportation will ultimately evolve from "silent reinforced concrete" into an intelligent organism that "thinks and warns."
