US 90 Signal Phase and Timing (SPaT) Project

Florida Department of Transportation


1. How SPaT can serve as a first step in the deployment of connected vehicle technologies.

2. The importance of field reviews, placement of devices and how to develop an understanding of the geography of the roadway in order to deploy SPaT.

3. The importance of obtaining FCC licensing for both road side units (RSUs) and on-board units (OBUs) by FCC-approved labs.


The Signal Phase and Timing (SPaT) Challenge is a challenge to state and local public sector transportation infrastructure owners and operators to cooperate together to achieve deployment of DSRC infrastructure with SPaT broadcasts in at least one corridor or network (approximately 20 signalized intersections) in each of the 50 states by January 2020. SPaT broadcasts are expected to be accompanied by MAP and RTCM broadcasts. The main purpose of this challenge is to provide SPaT and geographic intersection description information to motorized and non-motorized road users through a connected transportation system. A SPaT message defines the current intersection signal phases and can come from a traffic signal controller via a standard query protocol. Most DSRC roadside devices broadcast it as a standardized data message.


In the fall of 2016, the Florida Department of Transportation (FDOT) pursued the AASHTO SPaT Challenge and selected US 90 (East Tennessee Street/Mahan Drive) in the city of Tallahassee for deployment. The selected SPaT deployment corridor runs from Duval Street in downtown Tallahassee to Walden Road, west of Interstate 10 (I-10). (see figure to R)

The city agreed to partner with FDOT to install the SPaT equipment at the 22 signalized intersections and to help integrate the SPaT equipment with the Connected and Automated Vehicle (CAV)-ready traffic signal controllers.

The corridor at the west end connects the downtown area, the Greyhound Station and Leon High School, and the east end leads to I-10 which makes this one of the most important corridors in Tallahassee for business development and economic growth. The city installed traffic signal controllers along US 90 that were compatible with the SPaT/CAV software/hardware.

The short-term goal is to verify if SPaT will work effectively in hilly and forested terrain along US 90. The overall long-term goal is to evaluate DSRC efficiency and safety for road users along a signalized arterial corridor. FDOT engaged Florida State University to evaluate the operational and safety benefits of the SPaT applications along US 90.


This project is the first of its kind due to its magnitude and the scale of the RSU deployment in the state, and perhaps in the nation. The project has over 31 RSUs installed on 22 signals. Some of the major lessons learned during this process are the following:

  • Federal Communication Commission (FCC) Licensing: The state of Florida has a statewide Federal Communication Commission (FCC) license for testing DSRC. As DSRC units are installed, only specific site information is needed to complete the licensing process. FDOT’s statewide license will save time for any new deployment projects in the state.
  • Field Review: Conducting a field review of the corridor is important. RSUs are omni-directional and can emit as far as 300 meters (984 feet). However, consideration needs to be made for line of sight issues such as vegetation, road curvature, signs and intersection geometry. If a line of sight issue exists, adding another RSU to the signal location should be considered.
  • RSU Placement: The US 90 project tested RSU antennas on both mast arm and span wire configurations, and both worked well. Each DSRC antenna should be placed at a location to capture all approaches and follow the FCC requirements on antenna height placement.
  • Cabinet Location: The antenna should be placed on a mast arm on the same side of the roadway as the traffic signal cabinet location to minimize cabling or adding underground conduit.
  • Cabinet Space: For some CV-ready controllers such as the 2070 or Advanced Traffic Controller (ATC), as was the case in US 90 project, there is minimal space required for Power over Ethernet (PoE) injector placement. For others, a small digital versatile disc (DVD) player may be needed to convert controller messages to Society of Automotive Engineer (SAE) requirements, and to send to RSUs.
  • MAP Data Preparation: This project used the United States Department of Transportation’s (USDOT) mapping tool to develop map data for all 22 locations. Interested entities should consider working with vvendors to create MAP data that are interoperable, per the SAE standards.
  • FCC-Certified RSUs and On-board Units (OBUs): It is important to obtain the FCC licensing for both RSUs and OBUs by FCC-approved labs. Ask vendors to provide certificates during the procurement process and to include them in their document submittal.
  • Vendor Training and As-Needed Installation Support: Vendor training and field technical support (as needed) should be included in the contract. They should be identified as separate bid items.
  • Future Compatibility: Consider dual-band RSUs that have cellular/Wi-Fi capability as well as 5.9 GHz DSRC communications.

These emerging and connected vehicle technologies are a part of FDOT’s Transportation Systems Management and Operation (TSM&O) Strategic Plan that was adopted in August of 2017.

FDOT is teaming with various initiatives and agencies including SunTrax from Florida’s Turnpike Enterprise; the Central Florida Automated Vehicles Proving Ground; the Tampa Hillsborough Expressway Authority; the Central Florida Expressway; the cities of Gainesville, Tallahassee, Tampa and Orlando; and Florida’s university partners and research institutes, to address the safety and mobility needs of all road users.

Operations Area of Practice

  • Traffic Signal Timing
  • Connected Vehicles

Content Type

  • Case Studies & Lessons Learned

Publishing Organization

  • NOCoE

Document Downloads

Issue Date
April 10th, 2019
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