[cmsmith]

I think your assumption of equal time for each task is incorrect. Either because people don't dry their hands, or it doesn't take as long as washing.

Because typical bathrooms have 4 times as many sinks as they have hand driers, and I still see sink lines more often than drier lines.

[roc]

Only because "air drying" is a more acceptable option than "not washing". So a combined station would only slow things down inasmuch as people no longer skip drying.

In general (at least in the US) drying takes far longer than washing. Because most people wash quickly/poorly whereas driers are on timers and most are horrible.

And when your hands are still wet even after negotiating the unresponsive sensor and waiting an entire drying duration, it's understandable that many people would just as soon skip it.

[rytis]

OK, but still that doesn't change the equation. 22 secs washing and 8 secs drying is still 30 secs in total, whether it's done separately or not. And as you mentioned, the number of sinks and the number of dryers are balanced, so they combined have a similar throughput. I think you see sink lines more often just for that reason, if the sink line can handle 10 persons per minute, and the supply is 20ppm you will have a queue. But once we throttle people at the sinks, the supply to the driers is 10ppm, thus no lines (assuming the driers line is 10ppm)....