A SPaT Data Transmission Latency Analysis Compared DSRC Links Having Shorter Range and Low Latency (Less Than 2 Milliseconds) Against Cellular Links Having Longer Range and Higher Latency (Greater Than 40 Milliseconds).
A Federal study analyzed latency differences between dedicated short-range communications (DSRC) and cellular to assess the feasibility of using these methods for connected and automated vehicle applications.
Made Public Date
04/30/2021

932

Virginia
United States
TwitterLinkedInFacebook
Identifier
2021-01023

Feasibility Study and Assessment of Communications Approaches for Real-Time Traffic Signal Applications

Background

Connectivity to real-time traffic signal data is a key component of Connected Vehicle (CV) applications. This field study analyzed the latency differences (analogous to delay) between two communications approaches—DSRC and cellular 4G/long-term evolution (LTE). The Virginia Connected Corridor (VCC), a cluster of more than 60 intersections in northern Virginia equipped with roadside units (RSUs) served as the testbed for this study. Results from the study were used to assess the feasibility of these communications approaches in supporting different types of connected and automated vehicle (CAV) applications that use signal phasing and timing (SPaT) data from infrastructure systems.

SPaT data was collected at three separate intersections within the VCC, including a 4-way intersection in dense area, a T-type intersection near a small shopping center, a major arterial, and a nearby interstate corridor in a suburban area over rolling hills. Two data delivery paths were explored:

  1. Cellular (SPaT messages broadcasted from RSU to be received on a laptop via a VCC cloud-based system; and
  2. DSRC (SPaT messages broadcasted from RSU to be received on the OBU).

Data collection occurred over the course of one day at each site and was broken up into separate morning and afternoon sessions, wherever possible, to cover different levels of traffic demand. Data was collected over runs of 60 to 90 minutes.

Lessons Learned

SPaT data were collected at three separate intersections within the VCC, including a 4-way intersection in a dense area, a T-type intersection near a small shopping center, a major arterial, and a nearby interstate corridor in a suburban area over rolling hills. Two data delivery paths were explored: 1) Cellular (SPaT messages broadcasted from RSU to be received on the Laptop via VCC Cloud); and 2) DSRC (SPaT messages broadcasted from RSU to be received on the OBU). Data collection occurred over the course of one day at each site and was broken up into separate morning and afternoon sessions, wherever possible, to cover different levels of traffic demand. Data was collected over 60- to 90-minute runs.  Latency data logged at various locations and GPS locations logged during the tests were used to plot a spatial observation over longitudinal distance. Analysis on the distributions of latency for DSRC and cellular data (Table 1) shows that DSRC has a shorter range but very low latency (less than 2 ms), whereas cellular has a longer range but higher latency.

Table 1. Summary of average latencies and ranges using DSRC and cellular for all three sites.

 

Latency (Milliseconds)

Range (Meters)

Type

Minimum

Median

Maximum

Minimum

Maximum

DSRC

0.8

1.1

1.5

430.53

1365.5

Cellular

7.7

36.46

68

1171

3751

Source: Feasibility Study and Assessment of Communications Approaches for Real-time Traffic Signal Applications, December 1, 2020, ITS JPO

Feasibility test of four applications using DSRC and cellular suggests that receiving SPaT data over cellular might enhance the performance for applications such as Glidepath and traffic optimization for signalized corridors (TOSCo), as the delay induced by cellular may be negated by the message being received over a wider distance (Table). However, applications such as transit signal priority (TSP) and Red-light violation warning (RLVW), which require low latency, may not be supported by the cellular network.

Table 2. Feasibility of applications using DSRC and cellular.

Application

DSRC

Cellular

Hybrid ((DSRC and Cellular)

Glidepath

Yes

Yes

Yes

TOSCo

Yes

Yes

Yes

TSP

Yes

No*

Yes

RLVW

Yes

No

Yes

Source: FHWA.
*Cellular may be acceptable for TSP at speeds ≤ 50 miles per hour.

Goal Areas
System Engineering Elements