Since all four criteria have to be met for the area to be classified as a reshus harabbim, if even one criterion is not met, an eruv of tzuras hapesachim can be erected (Shulchan Aruch HaRav, O.C. 364:4; Bais Ephraim, O.C. 26, and Mishnah Berurah, 364:5).
 The text of Shulchan Aruch reads:
“What is a reshus harabbim? A street or marketplace that is sixteen amos wide, … and there are those who say that if it [the street or marketplace] does not have 600,000 people traversing it daily, it is not a reshus harabbim.”
Rashi is the original source of this criterion that the street requires shishim ribo traversing it in order that it be classified as a reshus harabbim, and not all of the Rishonim are in agreement with him. [The Bais Av (2:5:2) brings proof that the majority of Rishonim accepts shishim ribo as a fundament of a reshus harabbim (see also Shemiras Shabbos K’Hilchasa, perek 17, note 21, and Toldos Shmuel, 3:86:8; see also The Overwhelming Majority of Rishonim Maintain that Shishim Ribo is a Criterion of a Reshus Harabbim).] Since there is no unified opinion among the Rishonim, when the Shulchan Aruch (O.C. 345:7) mentions the criterion that the street requires shishim ribo it prefaces it with a qualifier, “vyeish oimrim,” there are those who say. Nevertheless, nearly all of the Achronim consider the criterion of shishim ribo an accepted fundament of a reshus harabbim (Taz, 345:6 and Magen Avraham, 345:7). The Aruch HaShulchan (Choshen Mishpat 162:1) maintains that shishim ribo is an accepted fundament to the extent that if one does not want to join his neighbors in their eruv chatzeiros because he wants to be stringent and not rely on the criterion of shishim ribo, his neighbors can compel him to join them.
However, since some of the Rishonim do not accept shishim ribo as a requirement for a reshus harabbim, there is a difference of opinions among the Achronim whether or not a Baal Nefesh should adopt the stringent position if there is no shishim ribo present. Most Achronim mention the requirement of shishim ribo traversing the street without stating that a Baal Nefesh should adopt the stringent position. This omission signals that the requirement of shishim ribo traversing the street is an accepted fundament in the laws of reshus harabbim and even a Baal Nefesh can rely on it. Additionally, some Achronim state that once we utilize a tzuras hapesach for a street that is sixteen amos wide it is accepted that a Baal Nefesh could rely on the fact that the street does not have shishim ribo traversing it (Kanah V’Kanamon, 5:56; Livush Mordechai, 4:4, and Bais Av, 2:9:3). Other Achronim maintain that a Baal Nefesh should adopt the stringent position and not rely on the fact that the street does not have shishim ribo traversing it. However, that is only where the sole basis for leniency is that the streets are lacking shishim ribo (Mishnah Berurah, 364:8).
It is important to recognize that when considering the basis for leniency there are two levels: a fundamental factor in the din of reshus harabbim such as mefulash or mechitzos and a tzad l’heter such as using questionable mechitzos. The Mishnah Berurah (Bi’ur Halachah, 345:23), quoting the Elya Rabah, states that even in conjunction with a tzad l’heter, a Baal Nefesh can be lenient and rely on the fact that the street does not have shishim ribo traversing it. How much more so, if we were relying on fundamental mitigating factors like the streets not being mefulash and the area having mechitzos, there is no doubt that the Mishnah Berurah ― and all the other poskim as well ― would agree that a Baal Nefesh could be lenient and utilize an eruv of tzuras hapesachim, since we have not met all the requirements of a reshus harabbim.
It should be noted that had the Mishnah Berurah (345:23) seen the Bais Ephraim (O.C. 26) in conjunction with the Mishkenos Yaakov (O.C. 120-122), there is a possibility he would have paskened like the Bais Ephraim that shishim ribo is an accepted fundament of a reshus harabbim, and he would have agreed that even a Baal Nefesh could be lenient and rely on the fact that the streets are lacking shishim ribo. See Bi’ur Halachah (208:9, s.v. Eino M’Vorech), where he states that he does not have the sefer Bais Ephraim (see also Toldos Shmuel, 3:81:7, 3:86:8; Bais Av, 2:5:2; Divrei Yatziv 2:173:1, and Even Yisroel, 8:36).
It is significant to note that Rav Moshe Feinstein zt”l considered the criterion of shishim ribo an accepted fundament of a reshus harabbim (Igros Moshe, O.C. 3:94, 5:19, 5:24:10); however, he had chiddushim in how to apply it.
 The poskim concur that the shishim ribo must actually traverse the street. Therefore, just the possibility of shishim ribo traversing a street is not sufficient grounds for the street to be classified as a reshus harabbim (Bais Ephraim, O.C. 26; Mishkenos Yaakov, siman 121 as he explains the shitos of the Shulchan Aruch; Michtam L’David, siman 2; Divrei Chaim, Addendum 3; Zivchei Tezdek, siman 102; Maharsham, 3:188; Sefas Emes, Shabbos 6b; Yeshuos Malko, siman 27; Minchas Elazar, 3:4; Tuv Yehoshua, p. 8, and Igros Moshe, O.C. 1:139:5, 4:87; see also The Overwhelming Majority of Achronim Maintain That the Shishim Ribo Has to Traverse the Street Itself).
Since the Shulchan Aruch uses the term shishim ribo ovrim bo it implies a thoroughfare in continuous use and not merely the presence of 600,000 people in the vicinity who would have the ability to utilize the street. Even Rav Moshe zt”l (ibid.) interpreted the criterion of shishim ribo ovrim bo to mean a thoroughfare in continuous use, such as an intercity road, which he maintained would need to have 600,000 people traversing the same section of the road (ibid., 5:28:16) on a daily basis in order it be classified as a reshus harabbim. Additionally Rav Moshe stated (ibid., 1:139:5, 4:87, 5:28:5, 5:29) that the criterion of shishim ribo ovrim bo when applied to a city would necessitate a population of at least 3,000,000 inhabitants (see Part 1: Shishim Ribo According to Hagaon Rav Moshe Feinstein zt”l). Only a city with such a sizable population could physically satisfy the condition of shishim ribo ovrim bo, 600,000 people collectively traversing its streets at one time. [However, Rav Moshe acknowledges that it is difficult to interpret shishim ribo ovrim bo as applying to a city (ibid., 1:139:5).]
 There are poskim who maintain that in order to classify the street as a reshus harabbim it is sufficient that the shishim ribo traverse the street most days of the year (Maharsham, 3:188; Minchas Elazar, 3:4, and Minchas Yitzchok, 8:32:1). However other poskim accept the simple reading of the Shulchan Aruch that the shishim ribo must traverse the street every day of the year, otherwise it would not be considered a reshus harabbim (Zivchei Tezdek, siman 102; Aishel Avraham, 345:3; Kinyan Torah, 4:40:7, and Igros Moshe, O.C. 1:139:5, 4:87-88, 5:28:16).
Rav Moshe zt”l also understood the literal interpretation of the Shulchan Aruch as meaning shishim ribo traversing the road itself on a daily basis (ibid., 1:139:5, 4:87, 5:28:16). Rav Moshe posits that when the Shulchan Aruch states as one of the criteria of reshus harabbim that the street has to have 600,000 people traversing it daily, the Shulchan Aruch was also referring to an intercity road where the shishim ribo would have to traverse the same section of the road every day. Additionally, Rav Moshe states (ibid., 4:88) that although at times Brooklyn’s beaches might be host to a million people, this in itself is not reason enough to prohibit an eruv of tzuras hapesachim because according to the Shulchan Aruch the requirement is that the shishim ribo has to traverse the streets on a daily basis.