The design of the Croxley Rail Link has been described as a "portakabin on stilts" by a politician who is concerned that the district is becoming a "guinea pig" for the development.
Three Rivers District councillors discussed the conditions of the rail link, which looks to connect Croxley station to Watford Junction, via two new stations and Watford High Street.
While permission for the link has already been granted by the government, the district council has been charged with the task of approving certain conditions, particularly those relating to the viaduct.
Three Rivers will be considering three of the 18 conditions, with neighbouring Watford Borough Council looking at the remaining ones.
Speaking at the sustainable environment policy and scrutiny committee on Tuesday, Conservative councillor, Paula Hiscocks, commented that it was a "hideous design".
The Rickmansworth representative added: "In my opinion, it’s a portakabin on stilts."
The viaduct’s design is part of condition 12, with other conditions relating to Highways Access and landscaping.
One of the overwhelming concerns amongst residents and councillors is that of the viaduct’s design.
Residents packed into Three Rivers House last week to receive an update on the project.
Councillor Hiscocks queried how much of a say the district council had on the design if they deemed it to be unsuitable for the area.
Claire Westwood, the council’s acting area team leader for development management, said that she had spoken with the applicant following last week’s local area forum and was told that grey was their "standard" design.
Ms Westwood said: "They (the applicants) essentially say that the lead steel grey is a standard natural colour that would normally be used for this structural work and they consider it best to avoid intensive impact."
She added that it would be difficult for the council to refuse the condition of design in regards to the colour of the viaduct.
Following councillor Hiscocks’ questioning whether the developers had built a viaduct similar to this one or not, Ms Westwood said they had not.
Councillor Hiscocks exclaimed that Three Rivers were therefore being treated as "guinea pigs".
Comments made from politicians at the sustainable environment policy and scrutiny committee were then passed on to a meeting of the extraordinary executive committee, which followed directly after the first meeting.
Members of the extraordinary executive committee discharged conditions for the design of the viaduct.
Yet politicians were advised that they could not discharge condition 11, which relates to Highways Access and condition 4, which refers to landscaping as not enough information had been supplied to the local authority.
Work is due to begin on the Croxley Rail Link in September, and is scheduled to be completed in 2017.