BDP architect and urban design director Tony McGuirk said the two options provided design challenges. He said: "The line to Watford has stations that will form beacons of regeneration from Willesden to Watford Junction. The Aylesbury line offers the challenge of integrating a 21st-century rail system into a rural environment."
CrossRail is a joint venture between the Strategic Rail Authority and Transport for London. It will have two lines, one running from east to west and the other south-west to north-east through the capital.
The BDP team will include structural and services engineers, and specialists in conservation, landscape, acoustics, lighting, sustainability and town planning. Cost planning and project management will be carried out by Claruspcm, a joint venture company between BDP and PCM.
CrossRail has been allocated a budget of £154m by central government to carry out feasibility studies.