Knowing more accurate footfall counts down individual corridors is essential for better planning of stations and services. And yes, it's also a boon to pricing

Knowing more accurate footfall counts down individual corridors is essential for better planning of stations and services. And yes, it's also a boon to pricing advertising along those corridors. No way to improve one without improving the other. But that's literally all they're getting from this: spatially granular and accurate passenger movements. They're not collecting personally identifiable data or even aggregated demographic metadata. Just footfall counts. (Read their policies: they just collect device MAC data, which is hashed with a salt that is destroyed on a daily basis. This allows them to trace MAC addresses through the network without ever being able to trace it to an individual.) But, yes, those footfall counts are relevant to advertisers. So? TFL isn't a profit-making organisation: everything they get from advertising is re-invested in operations and new infrastructure. Anyhow, you're trusting them with your life when you ride they're vehicles. They do a pretty good job with that. Trusting them with fleeting awareness of your MAC address seems like a much smaller ask.