Comment by theluketaylor

SkyTrain vs Seattle Link Light Rail is a fascinating contrast.

SkyTrain works because of a virtuous cycle of attributes: Full grade separation enables automation. Automation enables many trains per hour. Many trains per hour with short trains still has tons of capacity. Short trains means lower costs for stations, which as the article notes is a huge portion of rapid transit costs. Lower cost means building more transit for the same budget, so more transit gets built. More transit with great headways results in transit being the mode of choice. Take any one of these elements out and you can still have a functioning transit system, but the magic is missing.

Link light rail is so close to full grade separation but not quite there, so headways are limited by the grade crossing. With longer headways, bigger trains are needed to serve the same capacity. Bigger trains mean big stations and beefier, more expensive viaducts. Big stations are expensive.

Link is gaining ridership and offering great service, but it's hard not to think if they had learned the full lessons from nearby Vancouver it would be even better (and cheaper).