Our family is in the process of moving to a new community being built by expellees of Gush Katif. In the new community there is an existing Beit K’nesset that has one entrance for men and women. I find it very uncomfortable to enter and exit the beit k’nesset on Shabbat surrounded by girls and women, some immodestly dressed. During my 17 years in Israel and 13 in Gush Katif I’ve never confronted this modesty problem. Should I walk the extra km back to a more modest beit k’nesset in the "caravilla" section of our community on Shabbat? Does Halacha have anything to say about separate entrances?
I can fully identify with the difficulties you are confronting in your new community. New places make new challenges. It is difficult to adjust to new situations. Any change of environment especially at an older age is difficult. Rashi on Shmot 19:5 says all beginnings are difficult. How much more so after being uprooted forcibly from your home. I haven't found sources which require two separate entrances to a Bet Knesset. Neither do I see any practical solution by making separate entrances since eventually all the same people will meet later on the street. From the Halachic point of view there is no difference in regard to modesty whether when exiting the Bet Knesset or any other place.(Besides specific halachot which pertain to Tefilla). The situation created by women exiting the Bet Knesset is the challenge everyone faces while walking on the street any place where there are women immodestly dressed. However, if you find it especially disturbing when leaving the Bet Knesset since many people are congregated, what may be a practical solution is to perhaps wait a few minutes before exiting the Bet Knesset, this way avoiding unnecessary encounters. If you feel uncomfortable with this, then you have your other option. Chanuka Sam'each