 INSTRUCTION: You are a helpful search assistant that is given some documents with page number, document name and document text. 
             The User will ask you some question related to the document.
             Find and summarize the relevent Information from the documents for the User.
             Format the structure of the answer in academic format i.e cite the sources and make a list below the answer.

USER: whats the best device to monitor road weather conditions?
DOCUMENTS: [{'page': 0, 'source': 'Amount-of-De-icing-Chemical-Application-Note-B211799EN-A.pdf', 'document': 'several factors. For example, when the\nroad temperature drops below freezing it\ndoes not automatically mean that the\nroad is slippery; it only indicates that the\nroad will become slippery if the 
de‑icing\nchemical is diluted or temperature\ncontinues to drop.\nMonitoring Road Conditions\nDuring winter time, roads are treated\nwith de‑icing chemicals to keep them\nsafe. However, the treatment seldom\nlasts long.\nThe conditions need to be continuously\nmonitored to make sure that there is\nenough residual chemical on the road.\nRoad maintenance authorities must have\nenough reliable data available to decide\nwhen further treatment is needed and\nhow much chemical to apply.\nRoad weather stations provide this data\nfrom road sensor measurements. The\nmost relevant measurements are amount\nof chemical, concentration, and freezing\ntemperature.\nEach of these measurements requires\nthat there is a measurable amount of\nsolution on the road. The solution\nconsists of the de‑icing chemical that has\nbeen applied on the road and the\nprecipitation that has formed on the\nroad.\nFreezing Temperature\nMeasurement\nAt first glance, out of these\nmeasurements freezing temperature may\nappear to be the most useful observation\nfor decision making. However, the\nfreezing temperature measurement is\nhighly vulnerable to errors.\nRoad sensors are divided into two\ncategories based on the measurement\ntechnology: active and passive sensors.'}, {'page': 1, 'source': 'Amount-of-De-icing-Chemical-Application-Note-B211799EN-A.pdf', 'document': 'Freezing Temperature Does Not Indicate 
If Road Is Safe\nChallenges of Active Road\nSensors in Real Road\nEnvironments\nActive road sensors measure freezing\ntemperature by cooling and heating the\nsensor surface. The measurements are\nbased on measurement cycles, which are\nseveral minutes long and easily disturbed\nby splashing water or tires running over\nthe measurement point. When the\nmeasurement cycle 