The quickest and easiest way to travel from Arusha to Dar es Salaam is by air, though it is expensive and your time in Tanzania should not be ruled by time. Traveling by bus you are experiencing Tanzania, both its people and its landscape. The local transport is a cheaper alternative to flying but the cheapest of all is to travel by bus. This is never advised nor recommended by tour operators. It is said that local transport is too dangerous. This is true if you hop onto any old bus. However, your traveling need not be dangerous nor frightening, as there are some good and safe bus companies operating in Tanzania.
The most well known bus company is the Scandinavia Express. They operate probably the best, safest and most comfortable transport between the two cities. It is, of course, the most expensive private bus option - at about US$25 per person - and to book in advance is essential - your safari tour operator can do this for you. In Arusha, the ticket office and starting point for Scandinavia is at Kilembero Market, which is close to the Shoprite supermarket. Scandinavia has recently been in huge debt and has had some of their buses seized by the police which made the headlines in the East African newspapers. It has also made booking in advance essential, as the fleet has been depleted.
The 'Dar Express' bus service comes a close second to Scandinavia or maybe an equal first place. They have different classes of bus either budget or luxury; only the luxury is recommended. The booking Office - is situated close to the Kimahama Bookshop [about 500m up hill from the Arusha Stadium]. It is essential to state that you want the first class bus, which should cost about US$20 per person.
Dar Express is, without any doubt, my favorite company and I recommend this company above all others. However, some of the coaches do not have a toilet, although this may prove a blessing, as traveling in the African heat, especially if you are sitting toward the rear of the bus, isn't so much of a luxury after most passengers have taken advantage of such a service. Remember that the journey is a long one - about ten hours.
If you opt for the cheaper end of the market, most buses leave Arusha from the Bus Station close to the 'Stadium'. Buffalo seem to be a favorite for tourists looking for a cheaper way to get to Dar es Salaam, as the traveling time is less on this service. Speed is not a good thing as most of the road you will travel is single carriageway. It is a winding, hilly road, and therefore slowly, slowly is the safe way to ensure a safe arrival in Dar es Salaam from Arusha.
If I were to recommend the cheaper coaches, I would say either Fresh Coach or Amazon Coach. I have used both and they travel at a less manic speed between the two cities. The ticket price must be negotiated and do not pay more than US$15 per person. The last of each of these coaches leaves Arusha Bus Station at 8 am sharp.
Tickets are usually sold by freelance workers in and around the bus terminal and as the commission is good - the more they charge the more pay they take home - competition is fierce. If you are a tourist, you will be targeted and you will be surrounded by enthusiastic ticket touts. This experience is not for the faint hearted. Hang onto your luggage, keep money, mobile phones and cameras safely tucked away [as you would as a tourist anywhere in the world] for pickpockets are rife.
Why the rush? Usually this is because as a safari finishes in the North of Tanzania the relaxation on the islands of Zanzibar is the next stage of the safari. The cheapest way to get there is by bus to Dar es Salaam and then the high speed ferry to the Spice Islands. A bus leaving Arusha may arrive in Dar between 2 pm and 4 pm. The dilemma is to get from the bus station to the ferry port for the last ferry to Zanzibar; which leaves the port at about 4.30pm.
If you want to leave Arusha and travel by bus to make the ferry crossing to Zanzibar in a single day, I would suggest you're leaving Arusha about 6am to ensure you are in Dar es Salaam by 2pm. This gives you a good couple of hours to get from the Bus Station into town and to the ferry to buy your ticket.
The alternative is a stop over in Dar es Salaam. Dar is a great African city so why not spend the night and enjoy an experience that most people miss? There are some great beach hotels on the north coast. The south coast is more remote, wild and much less developed, this area has some fantastic hotels that cater for the budget market.