According to this
document the projected travel time from Fairway to Downtown Cambridge is 29 minutes, which given a distance of 17 km, means a projected travel speed of 34km/h - as fast as B-D (line 2) (and thrice as fast as Finch West).
the reason for not going straight from Preston to Galt is because the true goal is to redevelop and turn hespeler rd into the new cambridge city downtown. Heres a great article explaining the hespeler rd vision:
https://www.cambridgetoday.ca/local...tage-to-reshape-key-parts-of-the-city-6214764
Much of the justification for the speed is the amount of dedicated right of way and using existing rail corridors to their benefit.
When it leaves Fairway it immediately goes up on a bridge to cross Fairway and the CP tracks, before running on a very short stretch of the River Rd extension, then once it reaches Highway 8 and River it runs on a bridge (crossing the Grand River, Highway 8 off ramp, some ugly terrain) all the way to King St in Sportsworld, and then its at the next station. Then it runs centerline underneath the 401 before it goes on yet another bridge to cross the Shantz Hill/Fountain interchange and the Speed River, then you're at Preston Station.
Then once you leave Preston you cross King St (a different King St) and go back up on a bridge structure to cross a property entrance and a CP line, before it runs on a dedicated corridor (existing freight corridor) all the way to Pinebush.
Then you run along Hespeler where it will be centerline, before deviating into the rail corridor at the Delta and taking that all the way to Galt.
Phase 2 has something like 3km of bridges and only runs on the street along King, Hespeler and a very short stretch of River so it can fly much like it does in the existing train corridors.
When I rode the ION last year it was crawling at the two turns on Hayward and Courtland. Like it was moving so slow I thought we were rolling to a stop.
I hope at some point in the future they can straighten out that stretch of tracks and get rid of those two tight turns.
Heading south approaching Hayward just has a weird signal block which causes the trains to slow way before they need to, when the ION originally opened they decided to open it while they were still figuring out kinks in the signalling system, they were having issues getting ATP to work but trains could operate under LOS with no issues so they did, once they figured ATP out and removed LOS in the dedicated corridors (Mill to Fairway, and Waterloo Park to Northfield) that the problem started, it happens at Hayward and around Erb in Waterloo. There's also not much that's able to be done unless the Region buys Graybar or the vacant land on Hayward to make a more gradual curve.