Unit 3 - Road Transport Noise

Question 1

three primary sources of noise from road vehicles

Answer 1

• power train (including combustion) noise
• rolling noise
• aerodynamic noise

Question 2

Power Train Noise

Answer 2

Power Train Noise results from the power unit and transmission including the engine, air intake, exhaust,cooling fan, gearbox, differential and drive shaft

Question 3

What is Rolling Noise

Answer 3

Rolling Noise is the collective name given to all those noise sources resulting from the movement of the vehicle including;tyre/road interaction, bodywork vibrations, suspension, and brakes.

Question 4

Aerodynamic Noise

Answer 4

Aerodynamic Noise arises from air turbulence caused by the movement of the vehicle through the air. Aerodynamic noise is a major component of internal vehicle noise levels at higher speeds..

Question 5

relation of transport noise to speed

Answer 5

Power Train Noise and Rolling Noise increase as the vehicle speed increases, but not at the same rate.

Question 6

Heavy vehicle at lower speeds noise spread

Answer 6

Heavy Vehicle at the lower speed (20 km/hr), Power Train Noise is dominant, but, at the higher speed (80km/hr), Rolling Noise makes a noticeable contribution.

Question 7

Light vehicle low speed noise spread

Answer 7

Rolling Noise becomes the major contribution as the speed is increased

Question 8

Relative contributions of transport noise sources as a function of speed

Answer 8

Relative contributions of transport noise sources as a function of speed

• under urban traffic conditions, heavy vehicle power train noise is the main contribution to the total noise.
• At higher speeds on motorways, the rolling noise from both classes of vehicles becomes significant, as does the power train noise from light vehicles.

Question 9

Combustion Noise

Answer 9

Four stroke engines have one power stroke when fuel is burnt in each four piston movements, whereas a two-stroke engine has one power stroke for each of two piston movements.

The total firing frequency for the engine will be given by a combination of the firing frequency of each cylinder,t he engine speed and the number of cylinders within the engine.

F is the firing frequency, s is the engine speed (revolutions (revs) per second) and n is the number of cylinders.

Question 10

3 types of Engine

Answer 10

The amount of noise generated by the combustion process is largely dependent upon the type of engine. There are three main types:

• Petrol engines
• Direct Injection (DI) Diesel engines
• Indirect Injection (IDI) Diesel engines

Question 11

different engine type in relation to Noise being directly related to the impact force generated

Answer 11

Noise is directly related to the impact force generated by the power stroke of the engine

• This force is greatest in Direct Injection Diesel Engine and so these are the noisiest.
• Indirect Injection reduces the rate of pressure increase during the power stroke and hence reduces the noise.
• Petrol engine have the lowest impact force during the power stroke and are the quietest of the three types

Question 12

Rolling Noise at higher speeds

Answer 12

As power train noise becomes less, the other contributions to the overall noise level becomes ever more significant. The rolling noise from the tyre/road interaction is the most significant.

Question 13

The factors affecting tyre/road interaction noise

Answer 13

The factors affecting tyre/road interaction noise are

• Vehicle speed - noise increases by between 9 and 13 dB(A) per doubling of vehicle speed.
• Weight of the tyre loading - the greater the tyre loading, the greater the noise level emitted.
• Tread Pattern - Only significant (+1 dB(A)) for tyre with regular transverse features that may generate tonal noise at some speeds.
  
  • Tyre Structure - Cross ply tyres are noisier than equivalent radial-ply tyres.
• Tyre Wear - noise will increase as the tyre wears.
  
  • Road Surface Texture - Road surface noise increases with its surface texture. - Ribbed concrete roads are the noisiest.
• Surface Water – A thin layer of water may quieten the tyre/road noise but once puddles form there will bean increase in the noise of between 1 and 10 dB(A).

Question 14

Where is Tyre/Road Noise is thought to arise from

Answer 14

• Aerodynamic Noise - the tyre generates vortices and turbulence as it rotates
• Air Pumping - air is trapped in the tyre treads as they are deformed on contact with the road andreleased as the treads emerge at the rear of the contact area. The release of the air results in pressurefluctuations that cause noise.

Question 15

Traffic noise surveys

defining limits

Answer 15

There is a problem of deciding what the limits should be as we are dealing with noise annoyance rather than noise-induced hearing loss, such limits are subjective.

The basis for subjective limits is found, usually, through social surveys of some kind.

Either carefully controlled tests on a small group of people or questionnaires administered in door-to-door surveys.

-The small group surveys take place either in a laboratory or at research sites where the noise level can be measured accurately

Question 16

example of a subjective survey for road traffic - small

Answer 16

• Anexampleofasubjective survey is one that was performed with a small group of people responding to vehicle noise during drive-by tests.
• The pass-by noise was measured, and, at the same time, the subjects were asked to rate the noise of individual vehicles, separated by class, on a six-point scale with undefined end points

Question 17

example of a subjective survey for road traffic - large

Answer 17

A large-scale social survey relating to traffic noise disturbance requires a large number of traffic noise measurements to be made,

• Allows the range of measured levels is representative of the exposure of the questionnaire subjects.
• There is a wide variation in the subjective response of individual people to a given noise, because of non-noise factors.

Question 18

what does Highways England, Design Manual for Roads and Bridges, LA111 give advice on and what indices does it use

Answer 18

Gives advice on the assessment of noise and vibration impacts during the construction of the road and after the road has opened (the operational phase).

LA111 uses the 𝐿𝐴10,18ℎ index for assessing road traffic noise

Question 19

Correlation between LA10,18h and resident dissatisfaction with road traffic noise

Answer 19

The correlations derived refer to ‘steady state’ long term dissatisfaction.

• This means that the traffic conditions are unchanging over a sufficiently long enough period for any short-term effects to have been eliminated.
• The indication of noise nuisance used is the percentage of people who say they are bothered ‘very much’or‘quite alot’ by traffic noise.

Noise levels above 55 dB(A) show is clear correlation between the number of people disturbed and the noise level measured by 𝐿_A10,18h. Below 55 dB(A) the correlation is less clear

Question 20

What does an Environmental Impact Assessment do

Answer 20

Environmental Assessment provides a framework for assessing and managing the noise and vibration effectsassociated with construction, improvement, use and maintenance of motorways and all-purpose trunk roads

Question 21

Vibration from road construction activities

Answer 21

A111 makes use of the Lowest Observable Adverse Effect Level (LOAEL) and Significant Observable Adverse Effect Level (SOAEL) .

baseline vibration level before start of construction work may be assumed to be zero.

For vibration levels during road construction, LA111 suggests

• 0.3 mm/s Peak Particle Velocity (PPV) = LOAEL
• 1.0 mm/s PPV = SOAEL.

LA111 suggest two levels of impact assessment: ‘scoping’ and ‘further’.

The impact of noise from road construction is determined with reference to BS5228 Part 1 (2009)²⁷.

Once the road is operational, vibration caused by road traffic is unlikely to result in adverse effects.

Question 22

LA111 requires a baseline noise level (BNL)

Answer 22

LA111 requires a baseline noise level (BNL) to be established before the road has been constructed and opened.

This is called a ‘do-minimum opening year scenario’ (DMOY).

This is compared with the operational level once the road is opened, called a ‘do-something opening year scenario’ (DSOY).

A distinction is drawn between the opening year and the ‘do- something future year’ (DSFY) which is defined as the 15^th year after opening

Question 23

LA111 scoping assessment

Answer 23

The scoping assessment for road traffic noise described in LA111 aims to determine whether a further noise assessment is required, based upon answering questions

If the answer to any of the questions is ‘yes’, the need for further assessment is established and an operational study area determined which includes:

1. noise-sensitive receptors that are potentially affected by the project
2. noise-sensitive receptors in areas where there is a reasonable stakeholder expectation that noise assessment is undertaken.

Question 24

Type Approval Testing for vehicles

Answer 24

As a result of Type Approval Testing, vehicle manufacturers are required to demonstrate that the noise emission from each version of a given type of vehicle conforms to the prescribed standard

Question 25

UK vehicle noise control

Answer 25

Requirement within the UK for motor vehicles to have a suitable exhaust silencer and for the vehicle to be drivenin a manner not likely to produce excessive noise.

Question 26

in-use Testing for vehicles

Answer 26

Enforcement agencies such as the police may carry out In-use Testing on vehicles that are in service on the road. In practice, the testing of the sound emission levels for vehicles at the roadside is beset with difficulties and is not used in the UK

Question 27

in-use noise controls for road vehicles in the UK

Answer 27

Other in-use noise controls are

• A prohibition on the use of car horns at night or when the vehicle is stationary
• A restriction on the sale of replacement motorcycle exhaust systems that do not conform to the original equipment specification. Establishing that an exhaust system will conform is covered by a British Standard (BS AU 193: 1983

Question 28

Description of CRTN

Answer 28

The “Calculation of Road Traffic Noise” (CRTN) includes a prediction scheme that requires knowledge of the traffic flow, road layout and topographical information of the site.

Within the UK, CRTN is recognised as the national method and has been used for the first round of noise maps.

CRTN was designed as a simple manual method that would be accessible to all and allows the use of graphs and look-up tables as alternatives to calculation from formulae

Question 29

suitability of simple manual format CRTN

Answer 29

In this simple manual format CRTN is suitable for the straightforward determination of the noise level for individual locations but it becomes tedious and difficult when multiple receptors need to be calculated or when the road layout is complicated

Question 30

computer program realisations of CRTN

Answer 30

To ease these difficulties, computer program realisations of CRTN have been developed.

• often embedded in noise mapping software.
• Such programs allow traffic noise predictions to be made for whole areas affected by the road scheme and can cope with complex traffic layouts.

o conversion from manual version requires the computer programmer to interpret the meaning of the CRTN method.

§ Can lead to a difference between the results obtained by manual and computer-basedmeans

Question 31

The CRTN Prediction Method

Answer 31

• Section I Prediction Method, calculation
• Section II Prediction Method (additional procedures)
• Section III The Measurement Method

Question 32

CRTN five steps

Answer 32

1. The road is broken up into a number of segments; each segment should cover a length of road in which thevariation in noise level will be no more than 2 dB(A).
2. The segment thus should be homogenous in terms of traffic variables, road gradient, curvature, and screening.
3. For each segment, the basic noise level at a reference distance of 10m away from the nearsidecarriageway edge is calculated. It is determined by;

• the traffic flow,
• the speed of the traffic,
• the composition of the traffic,
• the gradient of the road and
• the road surface.

4. For each segment the basic noise level is then corrected for propagation between the road and the reception point.
5. At the reception point the noise level is then corrected for site layout features including reflections from buildings and facades and the angle of view of the reception of the segment. Finally, the contributions from all thesegments are added together to give the predicted noise level at the reception point for the whole road scheme.

Question 33

Section II Additional Procedures.

Answer 33

There are specific cases were the general method does not work and CRTN includes bespoke provisions. These include;

1. Low traffic flow,
2. End of scheme,
3. Curved roads,
4. Multiple roads and junctions,
5. Houses fronting onto a main road,
6. Multiple screening
7. Combined screening and reflection effects.

Question 34

Section III Measurement Method

Answer 34

Although prediction is the preferred method, measurement should be used when;

1. traffic conditions fall outside the validity of the Charts,
2. traffic conditions are complex rendering traffic data unreliable,
3. measurement provides a more economic method.

Question 35

Shortened measurement procedure

Answer 35

For the purposes of the Noise Insulation Regulations within certain limits, a shortened measurement procedure applies.

The 𝐿_A10 is measured over 3 consecutive hours between 10.00 and 17.00.

Then arithmetic mean of the three consecutive hourly values, 𝐿_A10 (3 hour) is then reduced by 1 dB(A) to give the 𝐿_A10 (18 hour) value.

𝐿A10,18h = 𝐿A10,3h - 1 dB(A)

The 𝐿_A10,18h then may need to be adjusted for propagation, site conditions and for future traffic flows as appropriate.

Procedure applies when the 15-year 𝐿_A10,18h is less than 66 dB or more than 69 dB. Outside these limits,measurement over the full 18-hour period is required.

Question 36

DMRB Annex 4

Answer 36

Annex 4 of the DMRB includes additional advice on the prediction of road traffic noise to that published in CRTN which should be followed when assessing the impact of road schemes. This includes guidance on:

• predicting noise from dual carriageways using dual source lines;
• incorporating screening from barriers in the central reservation;
• vehicle classification;
• the use of forecast traffic data specifically speeds provided from a traffic model;
• surface correction from thin surfacing;
• extrapolation of predictions beyond the 300 m limit of reliability in CRTN;
• reflection from opposite façades;
• congestion management systems; and
• noise measurements.