You can easily be visible a mile away but you won't throw a beam for a mile.

Even with the brightest lights out there, you won't have to worry about blinding drivers. A car headlight is 1300 lumens and there are two for a total of 2600 lumens. There are only maybe 3 lights out on the market that put out that much light - Lupine Betty at 2600, Exposure has one, and Light and Motion has one (i.e. true lumens out the front).

J.