MichaelAMW
Member
- Joined
- 18 Jun 2010
- Messages
- 1,014
This is a question arising from my observations, looking out of the window, of HSTs approaching Didcot on the down main, taking the 70 mph crossovers to the down relief and then turning onto the avoiding line to head towards Oxford.
I am interested in why different drivers begin to slow down at different points.
In terms of various distances (Some slight rounding)
Single flashing yellow to junction signal to cross DM to DR 1208 yds
From junction single DM to DR, to junction signal for Oxford line 1343 yds
HST Stopping distance from 125 mph 1750yds
HST stopping distance from 70 mph 650 yds
Thus braking distance 125 to 70 mph 1100 yds
So, it seems to me, if the driver of an HST following this route began a normal braking application at the single flashing then the speed will be down to 70 mph by the junction signal on the down main and, if the junction signal doesn't clear up from a single yellow with the route indicator, there is enough distance to stop by the next signal, the junction signal for the Oxford line.
Finally the question: why do some drivers start braking at the double flashing yellow, bringing the speed down to approx 70 mph by the single flashing yellow and then coasting from there. They could safely keep at 125 mph until the single flashing yellow - and some indeed do so. It seems a waste of the benefit available from the infrastructure and could delay trains behind.
My sources:
http://www.rssb.co.uk/SiteCollectionDocuments/pdf/reports/research/T060j_rpt_final.pdf
http://www.signallingnotices.org.uk/scans/161/1994 - 65 Didcot.pdf
I am interested in why different drivers begin to slow down at different points.
In terms of various distances (Some slight rounding)
Single flashing yellow to junction signal to cross DM to DR 1208 yds
From junction single DM to DR, to junction signal for Oxford line 1343 yds
HST Stopping distance from 125 mph 1750yds
HST stopping distance from 70 mph 650 yds
Thus braking distance 125 to 70 mph 1100 yds
So, it seems to me, if the driver of an HST following this route began a normal braking application at the single flashing then the speed will be down to 70 mph by the junction signal on the down main and, if the junction signal doesn't clear up from a single yellow with the route indicator, there is enough distance to stop by the next signal, the junction signal for the Oxford line.
Finally the question: why do some drivers start braking at the double flashing yellow, bringing the speed down to approx 70 mph by the single flashing yellow and then coasting from there. They could safely keep at 125 mph until the single flashing yellow - and some indeed do so. It seems a waste of the benefit available from the infrastructure and could delay trains behind.
My sources:
http://www.rssb.co.uk/SiteCollectionDocuments/pdf/reports/research/T060j_rpt_final.pdf
http://www.signallingnotices.org.uk/scans/161/1994 - 65 Didcot.pdf