Grade-separated elevated Bus Rapid Transit (BRT) systems generally cost less to build than elevated light rail (LRT) systems for the same passenger capacity. This cost difference is primarily driven by the infrastructure and vehicle requirements of each system. BRT systems require less complex and less expensive infrastructure, such as dedicated lanes, simpler stations, and less extensive guideway structures. Buses used in BRT systems are also generally less expensive to purchase and maintain compared to light rail vehicles (LRVs), which are high-tech and costly.

The cost of building an elevated BRT system can range from $20 million to $50 million per mile, while elevated light rail systems can range from $75 million to $200+ million per mile. This significant cost difference is due to the extensive infrastructure requirements for light rail, including track construction, power systems, and advanced signaling. Light rail stations are more complex and costly than BRT stations, requiring larger platforms, multiple tracks, and extensive landscaping.

BRT systems offer flexibility and lower initial costs, making them an attractive option for many cities. They can be more easily adapted to changing demand and can be expanded or modified with relatively lower costs. However, light rail systems can offer higher capacity and speed, which may justify the higher costs in certain high-demand scenarios. The choice between BRT and light rail should be based on a comprehensive analysis of the specific context and goals of the transit project.

In terms of environmental impact, BRT systems typically have a lower environmental impact compared to light rail. Buses emit less pollution per passenger mile and cause less disruption to natural habitats during construction. Light rail, on the other hand, is often seen as a symbol of modern, efficient transit and can enhance a city's image, potentially boosting economic development and public support for the infrastructure investment.

The cost difference between elevated BRT and elevated light rail systems can be influenced by factors such as route length, station spacing, right-of-way acquisition, tunneling, and aesthetic considerations. These factors can significantly impact the overall cost of each system. For example, if the BRT system requires a more complex and expensive guideway structure, the cost difference between the two modes of transportation can be reduced or even eliminated.

While BRT has lower initial capital costs, lifecycle costs such as vehicle replacement and maintenance can be higher. Buses have a shorter lifespan than light rail vehicles and require more frequent replacement. However, the lower initial costs and flexibility of BRT make it a cost-effective solution for many cities.

In conclusion, elevated BRT systems generally offer a more cost-effective solution than elevated light rail for achieving comparable passenger capacity. The choice between the two should be based on a thorough cost-benefit analysis, considering specific project conditions, ridership forecasts, and long-term operational expenses.