After the crash, the basis of our current transportation system will remain intact. Roads will be broken up eventually, but it will take a few years. Railways will remain for even longer, but the locomotives will be useless for anything but scrap almost immediately.
The early use of the paved roads is obvious. If a party does not have to climb over and through the brush, it will be able to move considerably faster. Although it is quite likely many of the major road ways will be setup for ambush.
Interestingly enough, railways might proven to be much more useful. A small team of men with a pulley system should have little trouble moving the now useless trains off the tracks. They can be salvaged for parts. The rails themselves could be used for a long time. Small carts being propelled by horse or man power could be used to move much heavier loads over longer distances than a wagon powered by the same force. It might even be possible to use steam engines. Eventually, without maintenance, rust and decay will render the rails unusable. But, until then, survivors can make use of the rail system.
Perhaps the roads which will be the most useful over the long term will be the water ways. People in areas with lots of deep and wide rivers will find them very useful for transporting people and goods. Small river boats will be well within the abilities of any reasonably resourceful person. Although, unless they already have a working knowledge of boats they will suffer from the usual losses to trial and error.
For people with sea access larger boats might become very appealing. However, building, maintaining, and using boats of such a size are very advanced skills and difficult to master. Having said this, there is ample direct and circumstantial evidence indicating pre-historic peoples possessed very effective sea-faring boats. There is even a lot of evidence pointing towards them crossing huge distances over the ocean. Even if such epic voyages are not appealing to groups of people on the ocean, a sensible position to be sure, sailing out for the purpose of fishing might be very appealing. And with fishing boats comes the ability to build and use coastal ships for trade with neighbors up and down the shore line.
Some peoples might find advantage with using horses or wagons. Either would allow a person to move considerably further with more belongings than they could alone. There is some debate as to whether or not pastoralists must necessarily rely on agriculturalists, but having and using horses does not necessarily equate to pastoralism. Some concerns of note with the use of wagons are obvious and some are not. One of them is, naturally, can you build and maintain a wagon and it’s team? One of the ones most overlooked, however, is how useful will a wheel be on the terrain in question. Some people look down on the Ancient Egyptians and Maya for not inventing the wheel, without realizing in many climates the wheel is worthless. The Egyptians lived with deep sand and the Maya lived in dense tropical rain-forest. If you are living in the mountains or with dense ground cover after the crash, you may find the wheel is no longer an effective tool.
Ultimately the most effective and most commonly used means of transportation will be walking. Walking is easy, does not require a person to build or maintain special equipment, and is low upkeep. To prepare ourselves we should begin making a habit of walking now. The suburbanites who think half a mile is too far to walk will probably die during the crash having not left their sub-division.