Sometimes in development, it's easier to solve a problem in hardware instead of in software, especially when an end product becomes urgent. Later on in production, the software can be done, the hardware can be linked out on the PCB, and the parts ommitted.
Here's an example hardware solution, if you get the pulse, differentiate it, trigger a monostable, then average the output with an R & C. The resulting DC voltage is proportional to roadspeed, can be fed into the infineon's adc input. I'll let someone else do a schematic if this is an option you'd like to try.
Otherwise in software, you'll have to get your head round the infineon's counter/timer, interrupt service routine triggered by the input frequency, and read the period from the counter/timer. Me, I'd do a prototype in hardware because I'm lazy, then let a softy come up with the equivalent, so I can re-route the PCB minus the hardware I did, or leave it in if the softy is too busy that week.