There is a lot of choice when it comes to automated vehicle counter systems. Some are sophisticated, while others are just a wire across the road (pictured). In my research, I didn't find similar solutions to counting pedestrians.
To be clear, solutions do exist. The problems are that traditionally pedestrians were counted manually, by volunteer staff. This is not scalable. There is a commercial sector developing automated devices, but they are targeted primarily at retail — counting people coming into the store, not walking on the street.
I know that at least some fellow students would suggest having self-reporting mobile devices. While Apple, Google, some carriers do hold this data, I see two problems:
1) this data would not be easily accessible (if at all) to city planners and researchers.
2) this data would be lacking in poorer neighbourhoods, where less high-end mobile devices are present.
I'd like to find a cost-effective way to make this data available for study.