Lap timer

Hi relatively new to arduino I'm in year nine, And our school takes part in a energy challenge in which we construct three wheeled energy efficient vehicle which only carries one person at a time. When then race these vehicles for 24 hours around a closed circuit.

Now to the project i have been enlisted to build a automatic lap timer which then displays this time on a led dot matrix, now the thing that i need help with is i dont know what i can trigger the timing with wirelesly from pit lane?

You haven't told us how many vehicles will be on the track at any one time.
If there's only one vehicle going round you could use an infrared beam across the track. If there's more than one vehicle you'll need to 1) identify each vehicle individually, and 2) identify when it crosses the timing mark.

You haven't told us how wide your track is at the timing mark. This is needed to tell us the range your detector(s) will need.

If there is more than one vehicle racing, what do you want to do if two or more cross the timing mark at exactly the same time?

Is it indoors or outdoors? 24 hours means it would have to work day and night. Hmmm. I wonder if you could put vertical IR beam shining down onto a reflector in each lane.

Put a bar code on the bottom of each vehicle, and have bar code readers under glass that they run over?

Paint the bottom of each vehicle a different color, and have a color sensor that they run over?