WATCH_DOGS

Quick method

All I did was select the Interception fixer contract "Deadly Loop", from the fixer contracts app on your phone. Make sure you have the GL-94 pump action grenade launcher, if you don't have it buy form a gun shop. I'm not sure on the price, but money is easy in this game so that should not be an issue. Also I'm not sure when this contract becomes available im on act 4 mission 2.

This contract involves "taking down" killing two targets. When you start there will be a sports car parked to to your right facing the wrong way in traffic. Hop in and go the way the car is facing, take the first right underneath the L station, then your almost immediate left into the ally, Follow the ally to the next block and stop and get out just outside the next ally. Targets should be turning down the ally headed straight for you. Pull out your launcher take aim and blast the first car, the second one will squeeze though wherever he can so blast him too. Mission complete. If you miss, run out of ammo, or the cops get called. Blow yourself up cops will be gone and ammo refilled.
After you complete this once you will need to set a waypoint to be able to play again. This can be done in 27 sec, takes about a min to run back. Can be done from 0 in a little over an hour, once you get the rhythm down its quick.

Here is a video showing how to complete the achievement End of Line in under one hour, performing 40 fixer contracts, which could otherwise be a bit tedious one. The trick is you don't have to perform 40 different contracts, it's ok repeating the same short one. This one is easiest performed after unlocking the GL-94 Grenade Launcher but you can use IED's or Proximity IED's as well, same strategy and location.

So what you do is load up your phone and navigate to Fixer Contracts. Sort by Interception and select the contract Deadly Loop. This contract requires you to kill two separarate targets driving two fast cars.

After the cutscene, get into the nearest vehicle facing north. Funny enough a car (or sometimes a motorcycle) parked in the wrong direction will be provided for you. Drive north to the first intersection and make a right turn. Then almost imediately take the first left into an alley on the left side as shown in the video. Get out of the car and pull out your GL-94 Grenade Launcher. Now aim down the alley and wait for the two cars approaching and take them out. Contract done!

Use forcus if you have to, these are high powered fast cars. Also run a bit into the alley since it lowers the risk of some pesky civilian calling the cops on you. If so, use a Coms Jammer. Then rinse and repeat.

I started out using this method with 5/40 Fixer Contracts and finished up in about 40 minutes. This solution works on Xbox 360, Xbox One, PlayStation 3, PlayStation 4 and PC.

for this achievement you have to complete 40 Fixer Contracts. now you can complete fixer contracts that show up on your map but if you complete them and still need more to finish the achievement you can use your smart phone and choose a contract. simply push the D-pad up and select fixer contracts to choose a contract. you can choose the same contract and it will still count for the achievement hope this helps and good luck!

Fixer contracts appear on your map as a steering wheel. There are various fixer activities. Some have you race through checkpoints avoiding cops, some have you take out enemies, some have you deliver cars, etc. They ALL count. Fixer assignments start popping up fairly early in the game, although not all of them at once. I have yet to figure out if they appear 1 by 1 after a certain amount of time, or after you progress a certain amount in the story. Just keep doing fixer jobs and if by the end of the game you don't have this achievement, just keep playing and the fixer assignments should still be appearing.