hexagon789
Veteran Member
Probably simply not necessary. The 100 section saved comparitively little time for all the additional wear and tear. The 100 section ran from Balcombe to Gatwick IIRC with a short PSR back to 90 through Three Bridges - the 100 applied only to the Class 319s which operated the Connex Brighton Express.
I believe this section was signed as a plain 100 because back then only the 319s were 'officially' able to run at that speed.
When the 377s were introduced, there was a change to which classes operated particular services and the 319s were then used on trains which made calls at Gatwick Airport, with their especially lethargic acceleration on third-rail they were no longer able to attain 100mph.
The 377s which took over the Brighton Expresses have better acceleration than the 319s they replaced, so were more than capable of achieving 100mph on non-stop workings but they impose significantly greater track forces than the previous 319s do, consequently additional track maintenance and thereford expenditure would be required. Regardless, the time saved by the 100 section was about 30 seconds, so I think it can be understood why the limit was reduced back to 90mph.
Other than the short-lived section authorised for 319s as I outlined above, the BML has been 90mph max since the early 80s. (It was 75 before then.)