Complex sentence: When Viper opened in April 1990, it was the tallest and fastest looping coaster in the world, until the opening of the Steel Phantom roller coaster at Kennywood in May 1991, which had a top speed of.
Split into simpler sentences: When Viper opened in April 1990, it was the tallest and fastest looping coaster in the world. However, it was eclipsed by the opening of the Steel Phantom roller coaster at Kennywood in May 1991, which had a top speed of.