The Problem.
How can you tell the car behind you how hard you're hitting the brakes, using your brake lamps themselves?

The Solution.
Use LEDs already being adopted by major manufacturers for their brake lamps for vehicle-to-vehicle communication, and leverage low cost accelerometers where ABS isn't available to determine how hard you're hitting the brakes.

I once almost hit a car in bumper to bumper traffic because I had no idea how hard it was braking. LED brake lamps these days may light up faster, but they still don't tell me how severely the person ahead of me is braking; it's all left up to visual judgement.

I designed a system with my students Awaid, Manan, Bilal, Najeeb and Adil that detected emergency/ hard braking in a car, and alerted the car behind it of the impending hard-brake that would be required as well, all through the LED brake lamps. Furthermore, if the same receiver-transmitter design was fitted in every car in a convoy, then the leading car that brakes first, can notify all cars behind through a very low-fi 'multi-hop' method, thereby preventing a pileup.

The system was built for a cost of around $35 using basic PIC16F MCUs, because we skipped the complications of tying into a car's on board CAN-connected antilock braking system, and used highly calibrated accelerometers to detect rapid braking.

This work has recently been published as a conference paper at CobCOM - the International Conference On Broadband Communications For Next Generation Networks and Multimedia Applications, held in Graz, Austria.