Low-height noise barriers of about one meter in height placed along urban roads usually have open cuts because access control does not apply to them. In addition, by taking the surrounding landscape into consideration, the barriers may require various designs and materials. The authors first define the two indices of sound reduction effects such as insertion loss (IL) and section-averaged insertion loss (SA·IL), and then propose the methods for calculating the effects by the following types of barriers: (1)the infinite-length planter type which is considered as absorptive wide barrier; (2)the infinite-length panel type whose material has small transmission loss; and (3) the type with open cuts added on (1) and (2). The calculation methods for the planter type are verified by model experiments. Finally, the authors analyze the relationship between the sound reduction effects and the parameters for designing the low-height noise barriers such as evaluation section length, opening ratio, transmission loss of the material and so on.