You cannot stop people driving on a public roadway unless they have violated the driving laws. As a general rule while living in a free country and traveling by private carrier or on foot it is no one's business where you have come from, where you are going, who you are with or what the hell you are doing. Many many people besides drug couriers have private lives that they feel is no one's business but their own.You cannot just stop people going about their private business unless you live in Yemen or Cambodia or Algeria? someplace creepy like that.