Permanent Way question (upgrading)

[tom73]

If a stretch of track has a permanent 40 mph speed limit, what would need to be done to the track to allow a higher line speed? To most of us with no connection to the industry, one stretch of track looks much like any other.

 

[Boodiggy]

Could be from a range of things.
Probably too many to mention in one post and depends on what speed the track is being upgraded to.
It’s not only the track that limits speed either

 

[Joseph_Locke]

I'm sure there was a previous thread on this, but can't find it.

Track-only constraints:
Sleeper material, type and spacing
Rail section and joining method
Fastening type
Ballast depth
Curvature (including turnout speeds on junctions)
Fixed diamond limits on cant deficiency
Maximum cant in station platforms
"complex" S&C types (like tandems)

Civils:
Formation critical velocity
Bridge fatigue, lateral load and resonance issues

Signalling;
Signal sighting
Braking distances
Overlap lengths
Possible introduction of restrictive junction controls resulting from increased main line speed
Sighting times for unprotected level crossings
Changes to protection system design for protected level crossings
Changes to barrier-down times caused by slower trains after strike-in changes
Route Indicator provisions
Spacing between speed changes causing excessive numbers of speed signs
Existing multi-SPAD signals
Speed sign placement relative to signals and AWS magnet exclusion zones

Electrification:
Conductor rail ramp speeds
OLE construction type
OLE wire gradient
Speed sign placement relative to neutral sections

Train related:
train acceleration capability and maximum speed capability (there might be no point if no train could get to a higher speed)
Classification for non-standard differential

Multi-discipline:
Structure clearances
Aerodynamic limitations in tunnels or on station platforms
Provision of safe access for staff
Speed sign placement relative in tunnels, complex junctions and station areas
Timetable constraints (no point arriving earlier ...)