What enhances the visibility of signals on roads running east and west?

Adding backplates to traffic signals enhances their visibility, particularly on roads running east and west. Backplates are the rectangles of material that are mounted behind traffic signal heads. They serve to provide contrast against the background, making the signals stand out more prominently, especially in bright sunlight or during adverse weather conditions. This additional visibility helps drivers to recognize traffic signals more quickly, leading to safer driving conditions.

In the context of the other options, while traffic lights can be improved with the installation of new units, this does not directly address the existing signals' visibility in specific conditions like backplates do. Implementing flashing lights can be effective but typically serves to alert drivers to specific warnings rather than enhancing standard signal visibility overall. Marking lanes with paint aids in guiding drivers along the roadway but does not specifically enhance the visibility of traffic signals themselves.