February 22nd 2011
As the world now knows, the European Rail Traffic Management System (ERTMS) is the international standard for in-cab signalling. Level 2 has no lineside signals, relying solely on radio communication, using GSM-R, between the train and control centre. Track-mounted balises are linked to a control centre using an IP network which is also used to send information back to the driver via the GSM-R towers.
So when the Swedish transport authority Banverket decided to upgrade the 184km Ådalen railway between Sundsvall and Långsele, they naturally chose ERTMS Level 2 for the signalling. However, as this was to be one of the first ERTMS installations to include level crossings, there were obvious safety issues.
Main contractor Bombardier and data specialist Westermo were brought in to set up the communications system. Trackside equipment was linked to Banverket 's IP network via pre-existing twisted pair copper cables using DDW-225 Ethernet extenders from Westermo's Wolverine series. The SHDSL technology used by these devices allows data to be sent at a maximum speed of up to 15.3Mbit/s over short distances and at slower speeds up to 15km. A stable distance/noise level was achieved at 2.3Mbit/s over distances from 2-7km.
The high safety requirements called for a redundant network solution so Banverket specified two individual networks connecting to a duplicated set of control equipment. These networks are completely independent and link to the backbone on separate routers. If one should fail, full access to the entire route can be achieved through the parallel network.
Using Westermo's DDW-225 helped with reliability as it is designed for harsh environments and can operate over an extended temperature range (-40C to +70C). Significant costs were saved as there was no need to install a completely new fibre-optic network.