Look Both Ways
Look Both Ways is an Achievement for Halo 3 obtainable in the Legendary Map Pack. To unlock it, the player must obtain a Splatter Spree in either a Ranked or Social gametype on a Legendary map. This achievement is worth 50 Gamerpoints.
An extremely difficult way of getting the achievement is on Ghost Town. If one gets on the Mongoose and splatters 5 people in a row without dying, and without getting off the vehicle to kill someone else with another weapon, the player will receive a Splatter Spree and the achievement will be unlocked.
On Avalanche, the easiest way to obtain a Splatter Spree is with a Ghost, but can still be obtainable with other vehicles, such as the Warthog, but it is more difficult. If played on the Asymmetrical or the "Heavy Modified" versions of Avalanche, there will be a Brute Type-25 Chopper which can splatter vehicles by "crushing" them, allowing the player to get a Splatter Spree and the achievement will be unlocked, however, on Heavy, a Chopper will need to watch out for Type-26 Wraith, Banshees, Scorpions and Spartan Lasers.
Another possible way is by getting a game of Neutral Assault on Avalanche. Grab the Ghost and camp where the ball respawns. With luck, the other team will try to come and grab it on foot. When they don't expect it, boost in for the kill. This can take a while, depending on how often the other team sends someone out on foot. It is also dangerous if the opposing team anticipates you the next time, and show up in a warthog. The best thing you can do is boost away and hope they don't tail you. Also be careful of trip mines, as there is a spawn for one nearby. A clever opponent may drop one just before death.
It is also possible to get this achievement on the Mythic Map Sandbox. Just grab the Type-25 Chopper or Warthog and splatter five people in a row.
The Mythic Map Longshore has a ghost, and using it to get this achievement may also give you the Ghost Patrol achievement.