system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Those black rubber tubes that cross the road and appear to count cars. Why are they counting and who puts them there?
gpt
They're very simple and cheap methods to gather traffic data for road and traffic planning. They're generally put down by local government and/or highways agencies, or companies working under contract to them. Potential questions they could be asking:

* There are planned road works on this road. How much traffic will we need to account for to divert on to other roads?
* There are high rates of accidents near this point. How fast are people generally travelling?*
* The signals down the road are often getting jammed up. How many cars regularly pass this area?
* Are large numbers of people using this side street as a cut-through to avoid a main road?
* Are the traffic signals further down the road creating enough natural gaps for pedestrians to cross, or do we need a specific pedestrian crossing here?

In short, those tubes are an extremely cheap and effective way of measuring lots of things about traffic for planning purposes. There's also no potentially identifying information collected, so nobody tends to care about being monitored by them. 

[Edit]

*To answer a very common followup question, these lines are usually put down in pairs a few yards apart so that speed can be measured. Measuring speed with a single line is indeed very unreliable because of varying wheelbase lengths, but with two lines you're literally measuring the time to travel between two points which is exactly what speed is.