Which of the following would increase the number of impacts per foot provided by a vibratory roller?

Increasing the impacts per foot delivered by a vibratory roller can be significantly influenced by the roller's speed of operation. When the roller is slowed down, it allows for more time between each impact as it travels over a particular distance. This increased time results in the vibration mechanisms having more opportunities to exert their force onto the surface being compacted, thus raising the number of impacts delivered per linear foot.

In contrast, speeding up the roller would decrease the time available for each impact, reducing the opportunities for compaction over the same distance. Similarly, adjusting other parameters such as the speed of rotation or amplitude affects the characteristics of the vibrations but does not inherently correlate with an increase in impacts per foot as directly as adjusting the forward speed of the roller does. Therefore, intentionally slowing down the roller optimally allows for greater compaction effectiveness by maximizing the impacts per foot.