AB4Rail aims to identify and select alternative communication bearers (ABs) and selection of proper communication protocols for the Adaptable Communication System (ACS) of the Shift2Rail technical demonstrator TD2.1. The project will review the state-of-the-art technologies assessing their suitability for the ACS in terms of expected performance, economic sustainability, and status of maturity. A wide spectrum of potential technologies have been identified including existing optical technologies for visible light communications (VLC), powerline communications (PLC) and short/long range technologies for the Internet of Things (IoT). Yet, breakthrough technologies under development and available in the next 3-5 years will be evaluated such as High-Altitude Platforms (HAPS) and high throughput Low Earth Orbit Satellites (LEO). The selected ABs will be tested in the lab (TRL 4) and on field (TRL 5) using the laboratories and on-field test bed of Radiolabs. A liaison with technology providers will be established leveraging on the network of Radiolabs, being the first in Europe having introduced, in 2015, a multi-bearer telecom architecture with public and satellite operators for ERTMS. The selection criteria for application/transport communication protocols will be assessed by theoretical results and simulations using an ad hoc software platform for network emulation/simulation at IP level to be developed in AB4Rail. Furthermore, AB4Rail is synergic with other projects funded by ESA, Shift2Rail, and Italian Ministry of Economic Development addressing multi-bearer telecom solutions for the ERTMS evolution. Special effort is allocated to the dissemination activities with the goal to involve the rail, telecom, satellite stake-holders and the standardization bodies. The project coordinator will be Radiolabs, a no-profit research consortium already involved in two Shift2Rail projects, with Guglielmo Marconi University as a partner.