at peak: 最盛期{さいせいき}で、たけなわで、育ち盛りに(は)He is at his peak as an athlete.Summer is the time when demand for electricity is at its peak due to air conditioner use.
at the peak of: ~の絶頂{ぜっちょう}にShe was forced to quit her job at the peak of her career. 彼女はキャリアの絶頂で仕事を辞めざるをえなかった。
consequent upon the timetable revision of march 15 , 2008 , all of the outbound trains (except for limited express trains and local trains bound for sasayamaguchi ) have been operated directly from the jr tozai line at a peak period in the rush hour in the weekday morning (between 8:00 a .m . and 9:00 a .m .) . 2008年3月15日のダイヤ改正より平日朝ラッシュのピーク時(8時台)の下り列車は特急および篠山口行きの普通列車を除き全てJR東西線からの直通列車となった。