Estimation of time at red on the Digswell viaduct

The Digswell Viaduct, also called Welwyn Viaduct, is a railway viaduct that carries the East Coast Main Line, which has to narrow from four tracks to two to cross the viaduct, making it a bottleneck restraining capacity over this strategic transport route. This problem is exacerbated by Welwyn North railway station situated at the northern end of the viaduct, which blocks the line while trains are stationary, and by two tunnels to the north.

This characteristic make this part of the ECML an ideal test case for the Time Signal at Red (TSAR), the new KPI envisioned by Network Rail and recently implemented in trenissimo.

In this study the TSAR was estimated in four types of simulations:

• Theoretical minimum time at red.
• Minimum time at red in the most favourable conditions.
• Minimum time at red under realistic conditions
• Sensitivity of time at red towards the variation of multiple parameters.

The study allowed demonstrating the sensitivity of TSAR to an increase of traffic on the ECML, showing a sharp increment once the nominal capacity of the line is reached.