How did they prepare the way for the murderers?
Rashi: By putting up signposts marked 'Miklat' by all the crossroads. 1
Ramban: By making sure that the roads should lead directly (without curves and bends) into the Arei Miklat. 2
Rambam (Hilchos Rotze'ach 8:5): By removing all obstacles. They did not leave a mound intact, or a valley or a river without a bridge, in order not to impede a murderer who was fleeing there.
Da'as Zekenim (in Mas'ei Bamidbar, 35:12): As the Pasuk writes in Tehilim, 25:8 "Tov ve'Yashar Hashem al- Kein Yoreh Chata'im ba'Darech". Hashem made a path for murderers to flee and be saved ? How much more so for Tzadikim! Hence the Pasuk continues "Yadrech Anavim ba'Mishpat Velamed Anavim Darko."
To enable the murderer to reach it unimpeded.
Why does the Torah insert the 'Hey' in "Tachin l'cha ha'Derech"?
Bava Basra, 100b: To teach us that the road leading to the Arei Miklat should be thirty-two Amos wide, instead of the regular sixteen Amos. 1
See Torah Temimah, note 6.
What are the implications of "Veshilashta es G'vul Artz'cha"?
Rashi: It implies that the distance from the southern border to the first Ir Miklat should be the same as the distance from the first Ir Miklat to the second, from the second to the third and from the third to the northern border.
What is the word "Lanus Shamah Kol Rotze'ach" coming to include?
Sanhedrin, 18b: It includes a Kohen Gadol who killed be'Shogeg, who is also obligated to run to an Ir Miklat. 1
See Torah Temimah, note 7.
Seeing as the distance from the [southern or northern] border to the closest Ir Miklat was the same as between one Ir Miklat and the next, murderers at the border had to flee twice as far as those towards the middle of Eretz Yisrael?
Hadar Zekenim (citing Makos 10a): This is due to the fact that there were many murderers in Sh'chem 1 (in the middle of Eretz Yisrael 2 ). Da'as Zekenim and Rosh - therefore, the other towns were close, so that murderers be'Shogeg from nearby towns should come to Sh'chem 3 to kill the murderers be'Meizid. 4
Ri'az (in Makos 10a): Residents of Sh'chem who killed be'Shogeg needed to flee to another Ir Miklat. 5 Therefore the other Arei Miklat were nearby.
Perhaps due to the many murderers in Sh'chem, the other Arei Miklat were close, to 'attract' murderers outside Sh'chem, to avoid it having as many murderers as residents, in which case it cannot absorb any more murderers. (PF)
Oznayim la'Torah: A murderer who lived close to the northern or southern border had the option of fleeing to Chutz la'Aretz, 6 where, to make up for the disadvantage of living among Nochrim, he enjoyed the advantage of being free of the restrictions of living in an Ir Miklat.
Da'as Zekenim and Hadar Zekenim: The Gemara said that there were three towns (for only two and a half tribes) in Eiver ha'Yarden, and three in Eretz Yisrael proper, since there were many murderers in Gil'ad. We must say that there were many in Sh'chem, and even more in Gilad; which the Navi in Hoshe'a 6:8 describes as "Akubah mi'Dam" ('who waylay for blood').
Rashi (in Sh'lach-l'cha Bamidbar, 13:25, citing Megilah, 3a) writes that Eretz Yisrael is four hundred Parsah by four hundred Parsah. This is without Eiver ha'Yarden, since he is discussing the Meraglim's journey. The commentaries here ask why a murderer at the [northern or southern] border had to flee twice as far (a hundred Parsah, a ten day journey) as one towards the middle. They ignore the fact that the east or west coast is at least twenty days journey away, and perhaps even thirty-six! Avraham went to the Akeidah in three days. Yerushalayim is one day from the Yarden (Beitzah 5a). According to Rashi (Bereishis 22:19), he left from Chevron (one of the towns), so it is at most four days from the Yarden, and thirty-six days from the west coast! The calculation assumes that Avraham did not have Keiftzas ha'Derech - since the Gemara states in Sanhedrin 95a that this occurred [only] for Eliezer, Ya'akov and Avishai. Perhaps the towns were centrally located for the settled part of Eretz Yisrael; Tosfos (Bava Metzi'a 28a DH Chamishah) says that most of the land was vineyards and forests (but this is difficult - see POINT BY POINT SUMMARY OF TOSFOS there). She'elas Ya'avetz (1:127, based on Gitin 57a) says that Eretz Yisrael shrunk. Perhaps initially Yerushalayim was far from the Yarden, or the towns were centrally located based on how Eretz Yisrael will be after it shrinks. If the land did not shrink, in any case parts of Eretz Yisrael will be more than 200 Parsah from one of the towns. If the towns needed to be on a line (from south to north), had they been placed to minimize the maximum distance from any place on this line (the top and bottom are a sixth of four hundred from the border), this would also minimize the maximum distance from any place in Eretz Yisrael (if the line is in the middle, about 211 Parsa'os). We could reduce this a little (to about two hundred and three) if they were in a triangle, but then no city would be even within a hundred Parsa'os of Sh'chem. (PF)
This is difficult to understand however, since choosing other Arei Miklat further from Sh'chem would cause Sh'chem to be closest to more towns, and would increase the number of murderers who came to Sh'chem for refuge! (PF).
As the Gemara explains in Makos 10a: If there are no witnesses on either murder, Hashem will cause the Shogeg to accidentally fall on the Meizid in front of witnesses. Consequently, he will be forced to go into exile and the Meizid will die - so that each one receives his just punishment.
As the Gemara states there, in 12b regarding the Levi'im.
See Oznayim la'Torah, who explains with this the Kashya as to why the Torah writes "Veshilashta" ? See also Sifsei Chachamim.