This book may be of use to traffic engineers and researchers who are concerned with the conspicuity of traffic signs. The Manual on Uniform Traffic Control Devices advises that, "Signs should be placed on the right side of the roadway where they are easily recognised and understood by road users". Guidance is provided on the spacing and prioritisation of signs, and in some conditions, additional steps may be needed to ensure that signs are conspicuous. This book also provides federal regulations that have been put in place to ensure that traffic signs are visible at night, and discusses impacts on state and local agencies of maintaining traffic sign retroreflectivity.