Port Eglinton viaduct presents the biggest engineering challenges.
It spans a succession of roads and railways and a business district where modern utilitarian sheds rub shoulders with listed buildings such as the art deco police stables.
Environmental considerations include the existence of nearby sheltered housing as well as the effect of the viaduct on the streetscape along Eglinton Street, a four lane primary route into Glasgow.
Technical hallenges include avoiding siting any piers where they will 'sterilise' land - making it inaccessible or unsuitable for redevelopment. A box girder structure which allows flexibility in siting the piers has been designed.
Minimising sruption to the roads and railways during construction is another concern. The viaduct has to span the 60m cutting over the WCML on a skew without intermediate supports. A cable stayed bridge was considered but rejected because its impact would have been out of scale with the landscape.