Answer: Evergreens would be more effective than deciduous trees, but better yet would be an earth berm and better than that, the concrete noise control panels we see along major highways in some areas. It is difficult to make a specific recommendation without knowing about the growing conditions; there may have been a particular reason they specified the plants that they did. You might want to check with the landscape architects for the project and discuss the tree selection criteria with them. Sometimes a project is required to meet certain standards such as plant native trees, or plant trees from the approved street tree selection list, or similar restraints.
If the screen is temporary, Leyland cypress will grow quickly but this is not, in my opinion, a tree for long term use. You will find that the majority of evergreens eventually grow very large, so you might prefer a fence instead. However, a tree to possibly consider would be the holly; it is ornamental, evergreen, and prickly to deter children from crossing out of the school yard. Another group of plants to consider if the location is in full sun and well drained, would be the junipers. These are available in a variety of mature heights and widths and many suitable for informal or formal hedge use and many with uniform growth characteristics. One last suggestion might be the arborvitae, this is also available in a selection of mature sizes and is frequently used as a hedge or barrier.
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