Final Design:

The final design used was based off of design #3. After thinking through the pros and cons, design #3 seemed to be the one that would work. It used both kinetic and potential energy in the spring and arm of mousetrap. Not only that, but it had a strong base with wheels that were guaranteed to lead a straight path. After performing a few tests, some adjustments were made. Such as using fishing wire to provide a strong hold on the hanger.  Out of all the tests performed, the vehicle goes a distance further than necessary and stays in a 2 tile wide path. All the rules are followed and used. 

What was done?

To make the car, 3 paint sticks were overlapped on each other. Two parallel to each other and the last one broken in half in the middle of the two. Then pens were put in between CD's as wheels and axles. These were glued to both side of the paint sticks base. After this, a mouse trap (cut and adjusted) was glued into the middle of the vehicle. Attached to this was a piece of a hanger that had a hook attached at the end of it. From this hook, hung a piece of fishing line that extended the length of the vehicle. This line was then pulled back bring the hanger with it towards the back of the car. The fishing line was winded up on the back axle of the car over and over. When this was released, the car accelerated in a straight path at a steady rate.