There are 3 things you must focus on:
1. Build the dogs motivation with either food or toys ( I find toys work best with chase driven dogs) to give them an outlet elsewhere and improve their confidence, impulse control and focus on you.
2. Give the dog ample TIME to observe traffic at a safe range and work on building a positive alternative response.
3. Give the dog ample DISTANCE so the dog shows no reaction and reward heavily. Only then can you start to decrease the distance very slowly. This may mean starting in an environment with minimal traffic.
4. Keep sessions short and end on a good note.
5. Always set your dog up for success.
6. If your dog reacts YOU have failed on one of the three points above. Go back a few steps until you get the desired behaviour and work from there.