Buses suffer more than most other forms of public transport from congestion. As a result, the bus interchange runs less smoothly than other types and generally has a more chaotic air. Bus interchanges operate more effectively when there are dedicated bus lanes nearby, but these have the effect of restricting access by cycle or taxi. Pedestrian movement can also be problematic, since buses operate at street level rather than high or low level as with metro and rail systems. People movement and bus mobility can be in conflict, especially immediately around the interchange where reversing may be taking place. Buses also are a source of air pollution and noise, adding to the perception that bus travel is at the bottom of public choice.