amount of grade separation, station structures, traffic signal systems and vehicles. In the year 2003 a study edited by the german GTZ compared various MRT systems all over the world and concluded ″Bus Rapid Transit (BRT) can provide high-quality, metro-like transit service at a fraction of the cost of other options.″ In the year 2013 the analysis of a database of forty-two BRT projects, nineteen LRT projects, and twentysix HRT projects specified „In higher income countries ... an HRT alternative is likely to cost up to 40 times as much as a BRT alternative" and a surface LRT alternative about 4 times that of a BRT alternative. Operational costs of running a BRT system are generally lower than light rail, though the exact comparison varies, and labor costs depend heavily on wages, which vary between countries. For the same level of ridership and demand, higher labor costs in the developed world relative to developing countries will tend to encourage developed world transit operators to prefer operate services with larger but less frequent vehicles. This will allow the service to achieve the same capacity while minimizing the number of drivers. This may come as a hidden cost to passengers in lower demand routes who experience a significantly lower frequencies and longer waiting times. In the study done by the GAO, BRT systems usually had lower costs based on "operating cost per vehicle hour", "operating cost per revenue mile", and "operating cost per passenger trip", mainly because of lower vehicle cost and lower infrastructure cost. The initial capital costs of diesel BRT are also much lower than a trolleybus system. Proponents of light rail argue that during the Belle Epoque railway troops were capable of constructing makeshift rail infrastructure within days or hours, similar to what it takes to establish even the most rudimentary road infrastructure where none previously exists. An ambitious light rail system runs partly underground, which gives free right-of-way and much faster traffic compared to passing the traffic signals needed in a surface level system. Underground BRT was suggested as early as 1954. As long as most buses run on diesel, air quality can become a significant concern in tunnels, but the Downtown Seattle Transit Tunnel is an example of using hybrid buses, which switch to overhead electric propulsion while they are underground, eliminating diesel emissions and reducing fuel usage. Alternatives are an elevated busway or an elevated railway,