it always seems like a good idea to put trains along freeways. it makes planning a train trip almost the same as planning a driving trip. once i started riding the green line on a regular basis, it became clear that this is a good idea on paper only. the two pictures below show just one of the reasons why.
very few people i've ever ridden in a car with keep the windows open on the freeway. maybe it's because the wind is just too strong, but it also shields passengers from the concentration of pollution that forms from the sheer volume of traffic on a freeway. unfortunately, when standing on a train platform, there is no option to roll up the window.
there are other reasons having a train running down the middle of a freeway makes for a bad passenger experience. the rumbling and noise of the cars makes it hard to relax and even think. freeways' separation from pedestrian traffic adds another layer of complexity to getting on and off the platform. and, worst of all, stations tend to be located where freeway exits are, not such pedestrian friendly spots. on the other hand, the trains do get to run a lot faster, apparently fast enough to make an athens services truck smoke.