There are many ways to look up dream meanings. You kind of have to choose what you think was relevant and go from there. A lot of people keep dream journals on a nightstand so they can write things down right away while it is fresh.
I found these couple things since the Semi seemed to be a major part of your dream-
To dream of a car accident, symbolizes your emotional state. You may be harboring deep anxieties and fears. This dream may tell you to slow down before you hit disaster. You need to rethink or re-plan your course of actions and set yourself on a better path.
Semi Truck-
To see a semi truck in your dream indicates that you are feeling overburdened or that you are being taken advantage of. You feel that you are pulling more than your own weight and it is time that others share in some of the responsibilities. Alternatively, the dream symbolizes size, largeness and power.
Car Flip-
To dream that your car flipped over implies that some significant event is preventing you from achieving your goals. You feel that you have to put your own life on hold.
Car Crash
To dream that you are in a car crash indicates that your beliefs, lifestyle, or goals are clashing with another's. It may also represent a shocking situation or painful experience. Alternatively, car crashes may forewarn of your dangerous or careless driving habits.�In particular, if a car crashes into you, then it suggests that your lifestyle, beliefs or goals may be in conflict with another's. It may also be symbolic of a jolting experience or injured pride.
You can check out more here, if you want to look up using other things from the dream you felt had meaning -
http://www.dreammoods.com/
http://www.understandmydreams.com/?dream_id=138106