TRITON

If you're cruising along one of Britain's motorways and see a large white 7½ tonne truck coming towards you, it could be TRITON. This is the name of the Transport Research Laboratory's new, specially built, mobile research laboratory. TRITON is used by TRL's scientists to better understand the relationship between tyre noise and the texture of a road surface.

Today's standard noise measurement methods for road surfaces rely on statistical monitoring which measures the noise levels of a large number of vehicles travelling through a fixed test area. However, this method is quite site-specific and does not lend itself to assessing long lengths of road. In addition the method is, by its nature, unsuitable for examining the performance of individual tyres. Both of these problems were overcome by using a towed tyre with close positioning of the microphone, 200 - 400 mm from the tyre wall, and isolation from external noise sources such as the truck engine, other vehicles, etc. As the next step, real traffic speeds and placing the tyre in the wheel tracks was needed to achieve accurate and repeatable measurements.

Unique New System
TRITON uses a completely revolutionary approach using a specially designed truck body that incorporates an anechoic chamber containing a test tyre and Brüel & Kjær microphones. This chamber can be lowered until it almost touches the road surface and the test tyre and microphones are effectively isolated from other sounds. In fact the chamber is so effective that the tyre/road noise delivers about 100 dB but the background noise is limited to about 60 dB.

Benefit
The major benefit of TRITON is that measurements can made at real traffic speeds, at any location and on any road surface. TRITON is equipped with on-board positioning equipment so that measurements can be made along short trial lengths of road. The tests can be accurately and reliably repeated using different tyres and the tyre angle can be changed to simulate different road cambers. Additionally, the road and tyre surface temperatures can be measured, as can the internal tyre pressure.

PULSE™
Inside the anechoic chamber, seven Brüel & Kjær microphones capture the noise emitted close to the tyre. These are connected to a Brüel & Kjær PULSE™ Multi-analyzer. The eight-channel PULSE system measures and analyses the signals from each of the seven microphones, while the eighth channel is used for triggering purposes. The PULSE system is triggered at regular 20 metre intervals along the length of the road under test. Each trigger starts a new real-time measurement over fixed road segments to build up a noise profile of the road.

On-truck Control Room
In the sophisticated on-truck control room, TRITON gathers huge amounts of data that will enable TRL to help improve the design of both tyres and road surfaces.

Steve Phillips, Head of Tyre/Road Noise Studies comments, "We are currently evaluating the initial data from TRITON to determine the best way to present data and improve our understanding of the relationship between noise and tyre and surface properties. Even with the calculation power of Brüel & Kjær's PULSE system, it will take some time to investigate all the data and all the possibilities because we are well aware that, in the case of both tyres and road surface technology, changes made to reduce noise could adversely affect road holding performance and safety". Steve continues, "With TRITON though, we can now measure a wider range of road surfaces under a wider range of conditions and over much longer distances. All this can be done in real conditions without requiring any special precautions and, especially, without causing unnecessary disruption to other road users".

Quieter Motoring
"TRITON will be monitoring noise routinely around the trunk road network and we anticipate that it will help us to unravel the mysteries of the complex relationship between tyre noise and road surface texture so that we can, perhaps, all look forward to quieter motorways in the not too distant future", Steve concludes.

PULSE Flexibility
TRL's TRITON system is just one example that demonstrates the flexibility of the PULSE Multi-analyzer. PULSE provides the verification and reporting of sound intensity, noise source identification, sound quality, material testing and sound power.

So, the next time you see a large white truck on one of Britain's busy roads, it may be "delivering the goods" in a rather different way!