An "acceleration road" is not a standard term in transportation engineering or road design. It's possible you're thinking of one of the following:

* Acceleration lane: This is a short lane on a highway or freeway that allows vehicles to increase speed before merging into the main traffic flow. It's typically located at the end of an entrance ramp or exit ramp.

* Acceleration ramp: This is a more general term that refers to the entire ramp, including the acceleration lane. It's designed to allow vehicles to safely enter the highway at a speed close to the traffic flow.

If you have a specific context in mind, please provide more information, and I can help you understand the term better.