Complex sentence: Highway 420 east of Stanley Ave is Roberts St and Newman Hill leading to the Rainbow Bridge to Niagara Falls, New York, which used to be designated a part of Highway 420 until 2000, when this portion was handed over to the City of Niagara Falls.
Split into simpler sentences: Highway 420 east of Stanley Ave becomes Roberts Street and Newman Hill leading to the Rainbow Bridge and Niagara Falls, New York. This portion used to be designated a part of Highway 420 until 2000, when it was handed over to the City of Niagara Falls.