There are loads of tactics for that. The "middle" that I described is very much a management tool, but depending on the level of the lunging you could also try throwing a handful of high value treats on the floor whenever you see a dog. If she'll put her nose down to sniff out those as the dog passes, you end up conditioning a response where a dog appearing signals treats on the floor and, resultantly, calmness. It depends on just how narrow the track is (will the other dog end up taking the treats, too?) and the level of arousal, obviously.