Advertising method in which a commercial is broadcast simultaneously on several radio stations and/or television channels is known as

Advertising method in which a commercial is broadcast simultaneously on several radio stations and/or television channels is known as a Roadblock.

Explanation:

1. The road blocking advertisement is an advertising strategy or a method in which a commercial is broadcast simultaneously on various radio stations and/or television channels.
2. This leads to blocking the road for the competitors to broadcast their advertisements. 
3. Roadblock Advertising is where all placements on the site are “roadblocked” with the same creative for the advertiser.
4. Roadblock Advertising allows advertisers to own 100% of voice for a given period, usually a day or could be the first-page impression of the day.
5. When this is run across multiple sites concurrently, roadblock advertising provides a wide-reaching media buy with similar metrics to those of TV media buy.
6. In other words, an advertising campaign would run exclusively across all the advertising units on a page reinforcing the advertising message.
7. Ideal for a brand or product launch when the aim is to gain brand awareness quickly.