Transport for London are running a campaign urging cyclists to make eye contact with drivers. It’s a great idea in principle. Unfortunately, it’s not possible in practice.

Whilst I was getting my hair cut this afternoon, a TfL advert came up on the local radio station they were playing. The voiceover urged cyclists to make eye contact with drivers to ensure that they’d been seen. That’s certainly something I try to do, but it’s very difficult, and I think it’s become more difficult over the past few years.

All modern cars have tinted windscreens. I don’t think they were always so widespread, but even commercial vans have them now. There’s a legal limit on how dark the tint can be: in the UK, they must allow 75% of the light through. However, if the cabin is ambiently lit, then the driver’s face when seen from outside can at best be only 56% (75% in times 75% out) as bright as everything else.

In addition to this, the windscreen is not perpendicular to the line of sight between the driver and the person outside: in fact, the rake of the windscreen means that it is generally reflecting the (bright) sky when viewed from outside.

Between reflections and the relative darkness of the cabin, you usually can’t see much of the driver from outside in daylight. You can’t make eye contact with a person you can’t see.

That doesn’t help much, I know. But if you’re driving, be aware that people outside—cyclists and pedestrians—might very well not be able to see you, no matter how much looking, nodding, or gesticulating you do.