The problem with many projects to speed up transit times is as one section is upgraded to past standards another slowly deteriorates to a slower speed. Look at the SW chief. Now when the Harold bypass is completed then you have a permanent improvement. Even the new Portal bridge replacement MAS (90 MPH) is just a rebuild as the original Portal had a 90 MPH limit that was reduced to 60 MPH due to determination. Granted there will not be the occasional delays due to bridge openings so on time reliability will improve.
The new Portal Bridge is supposed to have a higher clearance for ships, so that will reduce the amount of openings. BTW, when did Portal have a 90mph speed limit?