These databases include the complete articles across multiple newspapers and back in time for many years. Each one covers a different set of newspapers, depending on which publishers contract with the database provider.
One of the most effective ways to limit Google searches to useful results for research is to limit your search to particular websites or domains. Interested in finding only material originating from or related to academia? Search .edu domains. Only want to find information from government sources? Search .gov domains. Restricting to a domain can help you find government regulations or guidelines (.gov) or information from professional organizations (.org). Tired of seeing advertisements. Search site:-.com to indicate sites NOT in the (.com) domain.
traffic congestion site:.gov
...finds information about traffic congestion from government sites.
...locates information on the National Association of City Transportation Officials site relevant to congestion, and with the ease of Google searching.
traffic congestion site:-.com
...locates information on traffic congestion, excluding all of the sites that have .com URLs.