The pass, however, was a rough and narrow road with a series of steep slopes and sharp curves, so a bypass project to extend the road by 2.3 kilometers (including the 953-meter-extension with Sugasaka Minami Tunnel) was started in 1995 (Sugasaka Bypass).
しかし道幅が狭く、急勾配、急カーブが連続する悪路であり、1995年（平成7年）より菅坂南トンネル（延長953ｍ）を含む延長2.3ｋｍのバイパス道路事業（菅坂バイパス）を進めた。