Various Rishonim, early commentators, and many Acharonim, later commentators, have written extensively on this topic. Theoretically, persons on one side of the line would recite kiddish while the other side recites havdala. It may be possible for those who want two days of Shabbat to cross from west to east after shalosh seudas and start Shabbat again. Those who want to skip almost all of Shabbos could cross Main Street from east to west and go from sunset Friday to sunset Saturday. When is the eight day for a travelling infant in need od circumcision; the count of a niddah; etc.
מכתבים [הסכמות]: ר' שמואל ב"ר י[הודה] מאהליווער, ראדום, יד כסלו תרל"ו;
חיים זעליג ב"ר יעקב סלאנימסקי ווארשא, ח טבת תרל"ו.