recorded measurement data and accuracy

Information about things like number of lanes and speed limits may exist in the OSM database, but of course it depends on the mappers if the information is entered for a specific highway or not.

The maximum theoretical resolution of the map is 1 cm at the equator: How precise can OSM get?

The accuracy may be improved by summing up lot of GPS tracks, but on the other hand you don't know if the mapper drove the car in the middle of the street or more statutorily kept the vehicle to the right/left. So at least I tend to more trust my own tracks than the noise of other mappers.

Accuracy is on the whole not a top priority for OSM. GPS tracks can easily deviate 10 metres from reality, and the Bing aerial imagery we often use nowadays often only offers slightly better positional accuracy than that.

In theory, looking at the way we store coordinates internally, OSM offers a precision of one ten-millionth degree, or about 1cm. That's precision, not accuracy.

Averaging several consumer GPS tracks does help to get rid of measurement errors but there's a limit of how much you can achieve with that.

Speed limits available where recorded; check out the relevant wiki documentation where you'll also find a link to a specialist map depicting speed limits.

Lanes are usually not recorded with a geometry of their own but only as an attribute (e.g. "this road has three lanes"). No consensus has yet emerged on how turning lanes could be mapped in a useful way but discussions are ongoing.

1. There are very few highways with lane information yet. This might become more available as people map more and more details.
2. There is no limit to what information can be added to the map. You can open the 'Data' layer or the 'Edit' tab to see what information is added to the map.
3. The accuracy varies, some places have very accurate data due to good conditions and many mappers while other places have very poor accuracy.

The data comes from gps traces that you can upload for others to use, satelite images, surveys and some imports from other data sources that have been edited by hand to make the map. The more people we have walking around with a gps and taking notes and add it to the map the more accurate the map gets.