GLX already has a horrible bunching problem just with the at-grade junctions on the Huntington Ave. Branch. Northbound GLX service routinely has 20 - 27 minute gaps in service, followed by 2 or 3 trollies at once, with many of them going express. Otherwise it would be near impossible to run SUAG single digit headways. Of course if the T keeps it's terrible dispatching issues, then it would be needed to grade separate the GLX in full. The MBTA has to somehow make up the cost of providing terrible, terrible, terrible service on a brand new rail transit line.
"Median headway" of "9 minutes", but it's more like 15 minute headways at best. Barely even usable at all, and essentially forces the need of live updated timetables to even try to use the GLX.
(The image below
shows off peak service. This is the post-COVID era of WFH since it's not 2019 anymore, less peak oriented than pre-COVID, and off peak headways on the MBTA are terrible. However even
weekday headways often result in bunching with 15 - 20 minute gaps as opposed to 20 - 27 minute gaps during off peak hours).
West Medford being grade separated is a necessity. But any extra at-grade junctions after that will ever worsen the bunching problems more and more with a longer route and extra grade crossings. GLX past West Medford would already be adding a lengthy dose of extra runtime to its route milage through areas with relatively weak densities just to reach Winchester. At that point past West Medford, we'd need to give the GLX a dedicated downtown tunnel just to avoid the pain of running through the GL central subway tunnel.