Gemara

It says "ha'Boker Ohr" - the morning illuminated. This verse alludes to Rav Yehudah's teaching;

(Rav Yehudah): A traveler should stop [in the evening] and begin [in the morning] b'Chi Tov (when it is very light out).

Bava Kama 60a (Rav Yosef - Beraisa): "No one may leave his house until morning (on the night of Makos Bechoros)" - once permission to destroy is given (to the angel of death), he does not distinguish between Tzadikim and Resha'im (he kills both);

(Rav Yehudah): One should always start traveling and end traveling b'Chi Tov - "no one may leave his house until morning."

Ta'anis 10b (R. Elazar): "Al Tirgezu ba'Derech" - Yosef told his brothers not to engage in Halachah [on the journey back to Eretz Yisrael].

Question: R. Ila'i bar Berachiyah taught that if two Chachamim travel, and there are no Divrei Torah between them, they are worthy to be burned!

Answer: They should say teachings, but not investigate deeply.

(Beraisa): One who travels should not take a big step, and he should enter the city before the sun sets, like Rav Yehudah taught.

(Rav Yehudah): One who travels should not eat more than one eats in years of famine.

(Chachmei Bavel): This is due to digestive problems.

(Chachmei Eretz Yisrael): It is lest he run out of food.

They argue about one who sits in a boat (the only concern is for food), or one who goes from inn to inn. (The only concern is for digestive problems).

Rav Papa would eat a loaf every Parsah [about four kilometers].

He held that the concern is for digestive problems. (Due to his stomach, this was not a problem for him.)

Sotah 46b (R. Yehoshua ben Levi): One who walks on the way without an escort should learn Torah - "it is an escort of grace for your head."

(Rav Yehudah): One who escorts a guest four Amos in the city ensures that the guest will not be harmed;

Ravina escorted Rava bar Yitzchak four Amos. On his way, Rava bar Yitzchak encountered [what normally would] damage, and was saved from it.

Rishonim

Rashi (2a DH b'Chi): One should enter the city while the sun is still out, and in the morning wait until sunrise before leaving. The light is good for him. It saves him from wild animals and bandits.

Rashi (10b DH va'Yechanes): When the sun is out, bandits are not common. Alternatively, he will not fall in pits and crevices in the city, [and] people will not accuse him of being a spy or thief.

Tosfos (2a DH Yikanes): In Bava Kama, it seems that the reason to start and end traveling when the sun is out is due to Mazikin. We bring that once permission to destroy is given [to the angel of death]... If so, one must be careful even when leaving his city. The Gemara mentioned entering [the city] first because this is the normal way it discusses them, similar to "he climbs and ascends [out of the pit], and he climbs and descends [into the pit] (Eruvin 21a), which discusses ascending first. Regarding Bein ha'Shemashos, we say "this [day] enters, and this [day] leaves" (Shabbos 34b). However, in Bava Kama, Rav Yehudah expounds this from another verse! The Rashba answers that "ha'Boker Ohr" teaches about another city, even when there is no concern for Mazikim, e.g. Yosef's brothers. This is due to pits. The verse "Lo Tetzu" teaches about one's own city, due to Mazikin.

Poskim

Shulchan Aruch (OC 110:4): One who journeys prays "may it be Your will to lead me peace...'

Magen Avraham (10): One should engage in Torah on the road, but he should not investigate Halachah, lest he be distracted. Perhaps if one sits in a wagon and someone else conducts it, even investigation is permitted. One should not eat more than one eats in famine years, due to intestinal sickness. One should enter (the city in which he will lodge) and begin traveling when it is light outside. Tosfos (2a) permits at night in one's city if he is not alone, for there is no concern for Mazikim or pits.

Machatzis ha'Shekel (Sof 10, DH Lo): Even though it is dark, he knows the pits close to his city. Perhaps the concern for armed robbers applies [at night] even close to his city and even if he is not alone.

Birkei Yosef (3,4): I have a tradition that one should learn some chapters of Tehilim every day [while traveling] with intent and humility. This will be good for him. One should strive to have an escort, for then he will not be damaged.

Mishnah Berurah (20): The Gemara connotes that one who travels must hunger himself, for satiation is bad for the intestines. One should ensure that he has bread with him even if goes to a nearby place where bread is available, for sometimes mishaps occur. Everyone with Yir'as Shamayim should take with him Talis and Tefilin, even if he goes to a nearby place and intends to return today, lest something occur and he will [not return and] lose the Mitzvah. In our many sins, many travelers do not take Tefilin, and assume that they will be able to borrow. This is a great sin. Often they lose the time for Keri'as Shema and Tefilah while waiting until they get Tefilin. Also, they take whatever Tefilin they get, and are not concerned whether or not the knot of the head Tefilin is the right size for their heads.

Ateres Zekenim (1): The custom is to ask permission from Gedolim before traveling, and to get a Berachah. The source is from Berachos 3b, which says that they would consult with the Sanhedrin before going to war. Rashi (DH v'Nimlachin) explains that they would receive a Berachah.

Kaf ha'Chayim (21): If one went on the way and forgot something, he should not enter his house. He should ask someone to bring it out to him (Tzava'as R. Yehudah ha'Chasid 4).

Kaf ha'Chayim (23): One should take a flask of water for thirst, and [to wash,] so his hands will be Tehorim and clean at all times.

Kaf ha'Chayim (24): Before going one should give Tzedakah - "Tzedek Lefanav Yehalech [v'Yasem l'Derech Pe'amav]" (Tehilim 85:14). He should give every day [of the journey] before traveling. He should also learn before leaving.

Kaf ha'Chayim (27): One who travels should strive that people make him a Shali'ach Mitzvah, or he himself marks a coin and says 'when I get to Ploni, Bli Neder I will give it to Tzedakah l'Iluy Nishmas R. Meir Ba'al ha'Nes."

Kaf ha'Chayim (28): According to Rashi in Ta'anis, we are concerned even if he is not alone and goes near his city.

Kaf ha'Chayim (29): If one sits in a boat or wagon amidst villages where food is available, there is no concern [for eating as much as normal].

Kaf ha'Chayim (30): It is good to leave on Tuesday, on which it says twice (in Parshas Bereishis) "Ki Tov." It is best if he leaves before midday.

Bach (YD 157:5); The Rosh (Avodah Zarah 2:4) says that one may not pretend to be a Nochri. However, the Nimukei Yosef (Bava Kama 40a DH Omar) says that if they decreed to kill anyone who is called a Yehudi because he does not serve idolatry, one may dress like a Nochri to save his life and flee. I say that even if there is no decree, but he is traveling and there is more danger for Yisre'elim, one may dress like a Nochri, but without Sha'atnez. Most merchants and travelers do so.

Shach (19): Nowadays people do so on all roads, for all roads are established to be dangerous. The Tashbatz (416) forbids to dress like a Nochri on the road. We hold like those who disagree, brought in Maharik (88) and Terumas ha'Deshen (196) from Sefer Chasidim. Terumas ha'Deshen forbids doing so when the Nochrim forbade Yisre'elim to pass through, and he put himself in danger. There is different, for he did not need to pass through there. This is unlike most who need to travel, e.g. for income, and have no alternative.