The CB radio (Citizen's Band Radio) is a semi-mobile exchange communication system common on board freight carrier such as trucks. See Wikipedia for more background and technical information.
It allows the driver to communicate information between each others while en route. This would basically gives the chance to a hitch-hiker to assess other potential ride before being dropped somewhere.
Its usage is mainly common with truck drivers within certain countries such as Poland, Canada, the United States and France but can also be common with 'outback' car drivers. It can also often be present at the truck stop or offices dealing with transport carrier or the 'outback' (such as Natural Reserves and National Park in North America).
In Poland truck drivers commonly use CB Radio to help a hitchhiker to find a new driver during the ride. On rest areas a driver may approach any hitchhiker to offer a search for a driver (on the main road) within the range of the CB radio message transmission area.
Portable CB radio
You could buy portable CB radio gear and try to get rides like that. In the United States they cost about 70 US$. Please add your experiences here if you have tried this.