Once completed and put into service, at grade rail systems can generally be adapted to changing demand or conditions only by means of additional construction or equipment installation. Steel rail facilities and systems are, by their nature and construction, not adaptable or subject to easy reconfiguration. All adjustments or adaptations of at grade rail systems are limited to installation of crossing gates, safety barriers and fences, sound walls, traffic signals and other warning devices; and to the operating performance of the train vehicles themselves. Where specific hazards or traffic conditions may not be correctable by means of equipment installation, the speed and/or frequency of train operation may require adjustment.
The limited ability of steel wheel on steel rail systems to negotiate grades of more than four percent insures that even a minor change in elevation requires an extensive reinstallation of the track roadway. A change in street elevation of a few feet which affects at grade crossings necessitates hundreds of feet of track reconstruction to accommodate the new elevation.
The limited ability of at grade rail to negotiate small radius curves requires additional right of way at any major redirection of the system. An at grade system within a street right of way would not be able to transition to a crossing street and remain within the public right of way.
At grade rail cannot be easily or safely automated because of the risk of other surface activities such as traffic or trespassers entering onto the operating system itself. This technology is also limited in frequency of operations between trains (generally known as headway) because of its impact on surface traffic and also because of its limited emergency stopping capacity.
Where the negative impacts of at grade steel rail passenger systems have not been adequately anticipated or mitigated at street crossings or in residential or other sensitive environments or settings, adaptation of equipment and service operations has required significant modification of operations and equipment in order to mitigate negative impacts or safety concerns. In some cases the financial costs or the engineering solutions required for mitigating these problems cannot be achieved and the negative impacts or safety concerns continue unabated.