I've had an unrealized pet project on my personal to-do list for quite some time in a similar area - to estimate the speed of neighborhood traffic based on the

I've had an unrealized pet project on my personal to-do list for quite some time in a similar area - to estimate the speed of neighborhood traffic based on the doppler effect of their traffic noise while passing my house. I can't use radar/IR devices since there's I'm not directly adjacent to the road and the intervening land doesn't belong to me, and the substantial hedges make any line-of-sight sensing impractical.