Rose and Galen were nearly knocked from the path when a riderless, wild-eyed horse galloped by.

一匹无人驾驭的马儿疯跑过来，差点就把萝丝和加仑撞出小路。

youdao

The best known riderless horse was Black Jack.

VOA: special.2009.05.25

Synchronised fell first time round this year but continued riderless for another five fences before fracturing his leg.

BBC: Grand National: RSPCA urges scrap Becher's Brook

Most experts agree that an open oval such as the mile-long track at Churchill Downs would present problems for riderless horses.

WSJ: Kentucky Derby: Do Horse Races Really Need Jockeys?

Video of the annual riderless race in Ronciglione shows that horses there do make turns, although the surface is slippery and they don't seem to be running at full speed.

WSJ: Kentucky Derby: Do Horse Races Really Need Jockeys?