UAE stopover onthe way to Kabul - transportation

Dubai you can get around easily via the metro. Everywhere else in the UAE is very pedestrian-unfriendly--much more so, in fact, than Bahrain. In three days, you can see, at a maximum, three places, so you should probably forget about either Al-Ain or Sharjah, even if you rent a car. It's no problem to rent as long as you a valid license from your home country. In your shoes, I'd try to see two cities at the most. Parking is not really a problem, but finding your way can be, unless your rental includes an up-to-date GPS.

I would advice checking the daily average temperature first. UAE Summer hot like hell. Swimming on the beach during this time feels like swimming in a big bowl of hot soup.

Any particular reasons for wanting to see Sharjah? Or Abu Dhabi? Neither two are particularly remarkable places although each will have one or two interesting sights.

If you fly into Dubai airport you will actually be closer to Sharjah than most of Dubai. But it still doesn't resolve the problem of why bother going to Sharjah in the first place.

The metro is fine if slow and doesn't always go everywhere (there's no beach right by a metro stop). Taxis are quicker nd cheap by Western standards.

There's a bus that runs from Dubai to Abu Dhabi but I know nothing about it as it's only taken by subcontinental labourers and low budget tourists. Ditto to Al Ain.

By the way, Al Ain is merely ok. There's a rather boring old "palace" complex and a small oasis in the centre of the town, otherwise it's mostly sprawling and unremarkable. The desert outside Al Ain and Jabel Hafeet are worthy but you can't access either on foot from Al Ain.

Other than the metro in Dubai the UAE is really not geared towards inexpensive AND efficient public transportation.

tallybalt wrote : Any particular reasons for wanting to see Sharjah? Or Abu Dhabi? Neither two are particularly remarkable places although each will have one or two interesting sights.

just to see something different, real UAE so to say. it doesn't really matter if some places are not remarkable. if I can have a feel of how life is there, that would already be interesting.

I looked at pictures and I was thinking it would be an old crumbling town. it actually has building erecting in the sky everywhere and it looks quite polished. but that is still fine.
a few hours there would be good especially as it is very close to Dubai.

I don't really mind the heat, I was in Bahrain in late July and it was OK (incredibly hot but also dry so much more bearable).

Can't answer all your questions but these are from personal experience. By rental car I've been to Abu Dhabi, Al Ain and Sharjah along with crossing the border to Oman.

UAE in Sept is not just hot but humid.

Never paid for parking during the stay. Large shopping mall are free for a couple of hours otherwise just park on the street.

Emirates passenger get free shuttles to Al Ain and Abu Dhabi. Check their website.

There is an electronic toll expressway from Dubai to Abu Dhabi, not too expensive. You can take smaller roads to avoid it.

Traffic not as bad as SE Asia but jams are daily occurrence.

Sharjah is no more "real" than Dubai. Like Dubai the overwhelming majority of its residents are expatriates albeit lower income expats from South Asia, elsewhere in the Middle East and the Philippines. People generally only live in Sharjah because they can't afford Dubai so it functions as a working class suburb for Dubai.

If you want to see the "real" UAE as in Emiratis you're better off visiting the shopping malls. But I do gather what you're looking for and the older parts of Dubai - along the creek in Bur Dubai and Deira (Dubai Museum, Bastakiya and the Gold Souk area) are more interesting and historic than anything in Sharjah. The atmosphere is also full of character, although Emiratis don't live there anymore.

To get the "real" UAE you're better off heading for the far northern Emirates (Ras Al Khaimah) and the East Coast, as well as the sleepy oasis towns scattered throughout the desert and Al Ain Emirate. But none of these places are like Indian villages where you can stroll up and be in the thick of activity. Emiratis are very private people and lead insular, almost invisible lives, within the close confines of their houses and Land Cruisers.

Occasionally someone comes to Thorn Tree and say they want to see the "real" UAE but the UAE isn't going to be like India or the more traditional parts of the Middle East. It's a very modern country and very recently built. The worthwhile sights in the UAE are going to be the over the top modern construction - the Burj Khalifa, the malls, the Dubai skyline, Sheikh Zayed mosque in Abu Dhabi. Like it or not they have become the defining icons of the UAE. If you want history and culture you're better off going elsewhere. It's not my intent to say don't come to the UAE but I simply want to point out that one needs to be pragmatic about what they can get out of the UAE. There are worthwhile things to see and do but they may not match up with what you're expecting or prefer to do, so you need to be careful before spending half the day and suffering a lot of hassles to go somewhere in some elusive quest.

thanks a lot for this answer !
I was certainly mislead by what I saw in Bahrain (Manama is modern but I saw far more local people than expats and the small town across the bridge was very typical and the architecture was definitely old (and the funny thing is that there, I saw many expats, most were coming from Bangladesh).

anyway, for more "real", I will certainly try to visit Oman.

Public Transportation in Dubai and other emirates is very accessible(even in Sharjah and Al ain and note that cabs are even cheaper in other emirates than in Dubai). In Dubai, tourist destinations/malls can be easily reach through the Metro. Here's a link of what places you can visit using the metro:

Using the Red line : http://www.ladyandhersweetescapes.com/2013/02/tour-dubai-via-metro-red-line.html
Using the Green Line: http://www.ladyandhersweetescapes.com/2013/02/dubai-city-tour-via-metro-green-line.html

Just like zashibis told you, renting a car is no problem at all as long as you have a valid driving license. For me I would say finding your way is not really a problem as long as you have maps and GPS, :)