I think you could make this work with the laser aimed at the reflector across the lane, and something like a 5 cm by 5 cm solar cell directly behind the laser pointer, maybe with both inside a 10 cm dark plastic tube to block stray light. The solar cell should mostly ignore (integrate) flickering in the return beam.
Don't go with reflectance... it's best you have the "receiving" solar panel on the other side of the street and then just send the data by wireless means...