Some specific measures that can be used to reduce the effect of highway noise include __________.

The correct choice encompasses a variety of strategies that can be effectively employed to mitigate highway noise levels impacting nearby areas. Each measure listed has the potential to reduce noise pollution in different ways.

Setting lower speed limits for certain sections of a highway can result in decreased vehicle noise, as vehicles traveling at lower speeds generally produce less noise due to reduced engine power and tire-road interactions. This approach is particularly effective in residential or noise-sensitive areas where high speeds contribute significantly to overall noise levels.

Establishing alternate truck routes helps to divert larger and often noisier vehicles away from residential or quiet zones. Trucks generate a significant amount of noise, and by redirecting them to designated routes away from these sensitive areas, the overall noise exposure to residents can be substantially decreased.

Additionally, the enclosure of highways, such as through barriers or sound walls, can effectively absorb and deflect noise away from residential neighborhoods. Such structures are specifically designed to diminish the spread of noise, creating a buffer that protects communities living in close proximity to major roadways.

In summary, option D is correct because it combines multiple effective strategies that, when implemented together, maximize the reduction of highway noise, addressing the issue from different angles for the benefit of the surrounding communities.