Noise Sources
Noise is usually from transportation systems - trains, planes, and automobiles. On most sites, the Planning Policy Guidance note 24: Planning and Noise (PPG24) is used to decide the appropriate action for a noise level on a site.
PPG24 suggests that typical noise levels should be determined for all hours of the day and night. These levels are then sorted into four bands or Noise Exposure Categories. Each category suggests appropriate actions, from recommending that adequate noise protection is provided, to recommending that the local authority refuse planning permission.
Solutions
Before possible solutions are discussed in any detail, the noise levels existing on the site should be determined.
Usually, this is best done by direct measurement - deploying sound level meters around the site for a long enough duration to be able to comment on the 'typical' noise levels at various locations on the site. The detail and confidence of the comments can be limited if a survey duration (and cost) is limited.
Noise from road sources can be predicted using traffic flow data. There is some discussion as to whether prediction is better than a sample day noise monitoring (is the day of the survey is particularly typical? how accurate is the prediction?). The one advantage of the prediction method is that it does not require access to the site, and could therefore be undertaken prior to purchase of a site. Foreknowledge of the kind of noise protection that may be required may be useful to avoid buying a blighted site in ignorance. 
Noise Barriers
- Road and rail sources can be effectively attenuated by barriers. The effectiveness tends to depend on how high the barrier is and how close to the source the barrier can be. Sometimes, barriers are not a possible solution. For example - a site with an express train line at one boundary. A barrier answers the local authority's concerns over noise, but the barrier will have to 4 m high and so raises new objections to the development. Effective barriers have no holes in them. Therefore, trees and shrubbery are not very effective as noise barriers, but not being able to see a noise source can reduce the number of complaints about it (also background noise level is increased due to wind moving through trees, birdsong etc).