Technology that assists traffic sign recognition


Technology that assists traffic sign recognition

A new technology is likely to have a significant benefit on road safety. Vehicle manufacturers are looking to introduce vehicles with technology which attempts to read and interpret roadside traffic signals. It’s part of the move by manufacturers towards enabling speed assistance and automated driving. With the advent of this new technology, Traffic Sign Recognition (TSR) system, Austroads ran trials in Australia to examine the implications of TSR for roading operators. In August 2018, Austroads produced a report that investigates possible approaches to be taken, by Australian and New Zealand jurisdictions and industry to consistently support and optimise the outcomes from the introduction of TSR systems. The Austroad Report highlights potential changes needed to Australian and New Zealand traffic signs.

The Austroad Report includes a diagram illustrating how TSR technology functions and is able to affect vehicle speed.

TSR process

TSR Process. Source: Arup, Austroads

What are the implications?
The Austroad Report discusses many implications. Here are just a few:

  • Updating of Signs: The New Zealand Transport Agency (NZTA) has the primary role of implementing and approving signage in New Zealand, which results in New Zealand’s system being significantly more uniform than in Australia. The NZTA is currently in the process of developing a national database of signs with the aim that it can be updated with real-time data on the network (e.g. VSLS) such that mapping and software systems will be able to connect to it.
  • Smart coding of signs: 3M are currently developing an approach of embedding machine-readable code in traffic signs. This approach uses a smart coding that can only be recognised by machine vision systems. This could be a future aid to TSR systems. as the smart codes would refer the vehicle back to a central database for regularly updated information on the road. 3M is currently trialling the approach with the Michigan Department of Transportation along I-75 in Oakland County (3M, 2017). It is important to note that smart coding of signs relies on infrared cameras to be equipped to vehicles, whereas currently, automotive camera systems work in the visible light spectrum. Accordingly, road operators should continue to watch as this technology evolves, but continue to work on current TSR systems using shape and colour recognition.
Signs with coding

3M machine-readable signs Image: Business Insider / Austroads

  • Focus on Variable Speed Limit Signs (VSLS):
Variable Speed Limit SIgns

Variable Speed Limit Signs. Source: Austroads

Austroads discovered that Variable Speed Limit Signs appeared to flicker when observed through a camera in some instances and then in others did not. The flickering effect makes it difficult for the TSR systems to correctly recognise the displayed speed limit. In response to this challenge, specifications in NZ state that the displayed image must not appear to flicker to the normal human eye. Also, the NZ Standard and EU standard for VSLS both recommend that the frequency of emitted light from a VSLS should be no less that 90Hz.

Here is an image of the problem encountered in the instance when TSR viewed a flickering VSLS. There are blackened sections of the sign face.

VSLS LED flicker

Example of the effect of VSLS LED refresh rates – blackened sections of sign face. Source: Austroads

Recommendations
Austroads’ Research Report sets out their major recommendations to the industry and jurisdictions on TSR systems.

Click here to view our recommendations (PDF)

Click here to view the Austroads full report (free registration required).