The phrase "entrance ramp" refers to a part of a road or highway that allows vehicles to enter or join the main road, usually at a higher speed. Full definition
There were no other cars entering the freeway with me, and my circular entrance ramp was dry and all mine. (automobilemag.com)
This allows for «bubbles» to form in the crowd, dampening congestion ripples in much the same way that rush - hour traffic signals on entrance ramps smooth vehicular traffic flow. (discovermagazine.com)
Body sway is noticeable on highway entrance ramps. (autolist.com)