In major cities the delivery of the greater frequency of tram services through a city core sees this being resolved by grade separation, and putting the trams in a tunnel under the centre
I've also done a lot of work on the delivery of robust standards for installing steel rails in a range of pavements. In 1999 after the debacle of the 4 new generation tram systems falling apart with rails moving in the concrete and tarmac, I worked to revise the 1870 Tramways Act with a lot of detail on the mechanics of losing control of a bicycle when it hits a raised steel edge. I also looked at rail level crossings and the poor standards for the pavement surfaces in tarmac, timber, concrete & rubber, all of which had caused fatalities to pedestrians and cyclists using defective surfaces which had not been fixed (for Staines the fatality was 12 years after the inspection had called for the issue to be fixed!)
I now have over 10 years of recording the poor detail underlying the construction and maintenance of the Edinburgh Tram track that I really need to get collated as a detilewd piece, and would really like to get the resources to deliver this, based on over 60 years of working with transport systems (in 1968 I was helping to build a new railway line in Wales!)
Over 100 years ago the Caledonian Railway prepared plans for a double track tunnel under Princes Street with some of the core logs at BGS looking to be part of this work and confirming thet the ground conditions are a factor in the continuing movement of the highway pavements along the Edinburgh Tram route from Haymarket to Waverley
Yet along the tram route using the street above, almost every load transfer joint between each section of the upper track slab between these points has cracked (2 cracks about 30 cm apart, and lumps of concrete fall out with patches in a variety of styles, plus many steel frames for access chambers and valve covers come loose and sink with the tarmac falling out - because tarmac does NOT stick to steel at all well - with steel plates covering the worst holes - often for a year or more. This problem required a complete redesign and rebuilding of the on street section on Princes Street with the side shoulders of the track having the tarmac replaced by black coloured concrete before the line opened, but the tarmac still breaks away from the edge of this and sinks/cracks plus the blockwork also moving and coming loose (because it was laid with a slack bond & the gaps filled by brushing in a 'dry mix' mortar which then falls out as it gets loaded by traffic
Drawing from the 1963 project at Oxford Circus in London and a system used in Switzerland now to rebuild a road for the full depth of the road structure by placing a portable steel umbrella over the excavations and constructing the new road under the existing route with traffic still running overhead
https://www.ianvisits.co.uk/articles/50-years-ago-a-huge-steel-umbrella-for-oxford-circus-tube-station-8955/
From the Core logs this means that the digging along Princes street will be a mix of glacial clay and gravels over a fractured bed of shale with the existing Scotland Street Tunnel neatly in place to remove the excavated material in large quantities, continuously and with minimised dust and dirt on a covered conveyor out to the Water of Leith where it can be ferried away on barges for land reclamation as appropriate
Placing the trams under the main street also enables the ey stops to be moved to better places (Shandwick Place/Maitland Street to the Junction at Lothian Road, and St Andrew Square to a new atrium space directly linked to the lower level of Waverley Market and through to the main bridge across Waverley Station, with the old Scotland Street Tunnel as a pedestrian link to the North & Canonmills
With the new station locations a third or fourth track can be included to regulate the trams from each radial route and even turn services back when an intensive service may be required to move crowds from events (eg at Murrayfield running an intensive service between Haymarket and Edinburgh Gateway when the event ends)
With the tram route under the street the junction for Leith (and also for the Bridges/Regent Road can have track rising up in the centre of Leith Street as a way to sort out the mess of the at grade arrangements of traffic signals etc between York Place and Picardy Place. As in the original tram systems with this continued world-wide (Hong Kong, Toronto, Belgium - & original Glasgow tram routes) trams should run down the centre of the carriageway, and motor traffic should yield to allow pedestrians to cross to a tram stop (the law in Toronto, Hong Kong, Boston) when a tram stops there
It should be interesting to see whether a report or a safety bulletin is produced following the recent pedestrian injury after a collision with a tram on Leith Walk